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Want to connect Makerbot Replicator+ to Mac and several to USB hub
I am at a school with several Makerbot Replicator+ – a total of 9 of them.
So, they seem to print fine and I can hook up to two of them to one laptop (they are some Lenovo models from a few years back) using Makerbot Print. Well and good.
But I wanted to hook them up to my MacBook Pro (2020, OS X Catalina) with the USB cables, and the MacBook doesn't seem to "read" the printers, it's like they aren't even there. Makerbot Print (latest version) doesn't seem to "see" that they are hooked up. I checked the system prefs to see if the Makerbots showed up as connected USB devices and they don't seem to be there either.
Now, I am connecting via the USB cables and then through an adapter that connects the USB-A to USB-C. If I should just use a USB-B to USB-C cable (I ordered one to test it) then fine, I'll do that. I just wanted to check that there wasn't some other problem or if anyone else had this issue.
Next up: USB hubs. Makerbot says they don't recommend it, but sometimes I have to print out lots of stuff at once for student projects and I can't tie up multiple laptops for hours-long prints. I have done the technique of leaving stuff all night but that's hit or miss – if something goes wrong I am not there to stop the print (at least once something got unstuck from the build plate and I ended up with an extruder with the end encased in hard plastic like a stalactite. Unless I basically blowtorch it off... )
So, the question(s) is/are:
Any recommendations for USB hubs? (I would do wireless but that I am less sure of, and it seems easier, faster, and more reliable to link up through USB. The wireless connection always drops).
Any recommendations for the MacBook issue? Is it just a matter of finding the right cable? (it's certainly possible my $10 USB-A to USB-C adapter plugs aren't well designed, and I should just go for direct cabling)
Any recommendations for a good USB hub to link a Mac (or anything else) to Makerbots?
Thanks for your time and help. I do hope I am not duplicating a post but I don't see anything in my searches that addresses the specific issues I have; though it's possible I didn't use the right search terms.

you can run into bandwidth issues going the hub route- there is some point at which attempting too many simultaneous prints off a single port will not be worth it.  instead consider the sd card approach?

Also what do you mean by SD card approach? The Makerbots take flash drives, but my attempts to print off of one were unsuccessful (it seems to be rather hard to make the right kind of file, it won't work with STLs and I gave up figuring out how to make them .makerbot files)

My answer pivots entirely around my supposition that the Makerbot Replicator has a CH340 IC for the USB. It may not, in which case my answer is useless. It would help to know which IC is actually used to implement the USB interface on the printer control board. If you can take a photo and add it to the question that would be great... however, it should be possible to determine the IC used by search the web - but only if you know the model and version number of the controller board, which should be written on the PCB somewhere.

Further analysis (via the web) appears to show that the CH340 is not used for the USB - see at the bottom of my updated answer. Therefore my answer probably should be discarded and deleted as it confuses matters totally. You really need to check what IC is used by your board, for an accurate answer.

they might take x3g which just needs you to run a makerbot slicing software on your stl.  usually can be made from same software that runs printer off usb

You want to make a gcode file, not a makerbot file. The STL file describes the shape of what you want. The gcode file includes things instructions for like temperature, layer thickness, infill density, and speed in various situations.... all the information needed for the printer to produce not only the correct shape, but at the correct quality and with settings appropriate for a specific printer.

As print jobs can take hours, and completely take over the computer while printing, you're pretty much always better off going with the SD card or USB option. Also, a dedicated print station (often a raspberri pi) can work well. But printing directly from the computer is waaaaay down the list. There's just too much that can go wrong over the course of a long print job for a computer to be a good choice.

It would seem that the printer control board doesn't use a CH340 (see bottom of this answer) and therefore this answer should be ignored.

CH340 and OS X incompatibility
The reason your Mac might not see the printers could be down to the USB interface on the printer controller board.
If it is implemented by a CH340 (which is probably is, in order to reduce manufacturing costs) then, historically, MacBooks have a problem with the drivers for this device and its derivatives. That is to say, the OS has a problem - more specifically the device drivers used by the OS X kernel - as opposed to the hardware. There are a number of posts dealing with this problem, it is common on Arduino clones too, see here.
The third party drivers for the CH340(G) written for OS X are often poorly written and/or have shoddy documentation - although this opinion may be hotly debated, and I have no wish to expand upon.
If the USB interface, on the printer controller board, is implemented with an FTDI or a ATmega 16U2 then it will work fine. Unfortunately the solution is probably not to use the Mac and stick with the Lenovos (i.e. PC clone).
See the extensive answers to Can't connect Cura to my Anet A8 on OSX 10.11.6

As an aside, I gave up trying to buy/use cheap Arduino clones with a CH340(G), on a Mac long along, as it just wasn't worth the effort in trying to get the Mac to see it. I now ensure that either:

I purchase a slightly more expensive Arduino which uses a 16U2 (the more pricey FTDI chip is more rarely used on boards these days, but can still be found). Obviously, you don't have that sort of luxury when selecting a 3D printer.
I will use a PC instead, if the board has a CH340(G), or similar.

One possible solution
However, having said all of that, this issue may have been resolved in newer versions of OS X (post Mountain Lion, or thereabouts). This might provide a solution, Connect to ch340 on MacOS Mojave

remove all old drivers:
sudo rm -rf /Library/Extensions/usbserial.kext
sudo rm -rf /System/Library/Extensions/usb.kext

Now reboot the computer.
And then (very important, because it took me 10 cables to find the
right one) use a fully connected cable ;-)
Now I have these ports:
/dev/cu.wchusbserial1410
/dev/cu.usbserial-1410

Important note: Clearly, deleting kernel drivers (also known as kernel extensions, .kext) shouldn't be taken lightly. If you feel uncomfortable doing it, or don't know how to revert the process, by using a saved backup of the drivers, then please don't attempt this.
For completeness:

To back up the kext (before deleting it as shown above):
sudo cp /Library/Extensions/usbserial.kext /Library/Extensions/usbserial.kext.bak
sudo cp /System/Library/Extensions/usb.kext /System/Library/Extensions/usb.kext.bak

To restore the kext (after having deleted the kernel extension and then finding that it made no difference whatsoever):
sudo mv /Library/Extensions/usbserial.kext.bak /Library/Extensions/usbserial.kext
sudo mv /System/Library/Extensions/usb.kext.bak /System/Library/Extensions/usb.kext

Alternatively, instead of deleting the kernel drivers, you could just rename them to hide them, by adding .bak to the filename, like so
sudo mv /Library/Extensions/usbserial.kext /Library/Extensions/usbserial.kext.bak
sudo mv /System/Library/Extensions/usb.kext /System/Library/Extensions/usb.kext.bak

Then reboot. Check the printer connects or not. If not, then just restore them using the same commands shown above - so you just end up removing the additional .bak from the filename.

With respect to the quoted answer, I'm not entirely sure what is meant by a fully connected cable... There is a well-known issue that some USB charging cables - that look like normal USB cables - have only the power lines connected, and omit the data lines (again for cheapness), and it can be difficult to tell the two apart (usually by thickness, the thicker cables have more lines connected). Obviously, if the data lines are missing then the cable will not transfer data.
However, this usually applies only to cables with mini, or micro USB connectors, and usually doesn't apply to standard peripheral cables such as a USB-A to USB-B cable:

So, this issue should only arise for micro/mini USB connectors... it will depend upon your connector type.

We can't recommend particular makes or models of USB hubs as that is a shopping question, which is off-topic.

Analysis on the printer board
Makerbot appear to use the Mightyboard for the Replicator. INterestingly from the following two photos it would appear that a CH340(G) is not used, and the IC is in fact a 16U2.
Here is a photo of the board (image from MakerBot Replicator 2/2X Rev H Mightyboard – Official, OEM Board w/ 4 BotSteps):

The IC closest to the USB-B port would appear to be a 16U2:

Its form is square like a 16U2 and not elongated like a CH340G
It would appear to have an Atmel logo printed upon it.

This image (from MightyBoard Motherboard 3D Printer Dashboard), also suggests the a 16U2 is used:

All of which means that, if your printer(s) have this board, then your Mac should indeed connect to the printer.

OK, I am not one who understand much of the terminology you just used. But when you say a fully-connected cable do you mean one that does not need an adapter?

To put it bluntly, could you translate your post to non-techie?

I'm not entirely sure myself, as that is quoted from the linked answer. However, there is a well-known issue that some USB charging cables - that look like normal USB cables - have only the power lines connected, and omit the data lines (again for cheapness), and it can be difficult to tell the two apart (usually by thickness, the thicker cables have more lines connected). Obviously, if the data lines are missing then the cable will not transfer data.

Again thanks, and to be clear the "CH340" on the Mac side or the printer side? (Again, a big chunk of the answer you posted is pretty opaque to me). If I understand it correctly you are saying I can delete the USB drivers on the mac, reboot, and it should read the USB printer connection. I am a little nervous about deleting stuff like that from my system.

Updated answer... hopefully it is a bit clearer :-)

YES thanks, it clears up a lot of things (and you went all in with the illustrations!)

what do you mean by SD card approach? The Makerbots take flash drives, but my attempts to print off of one were unsuccessful (it seems to be rather hard to make the right kind of file, it won't work with STLs and I gave up figuring out how to make them .makerbot files)

This sounds like you need a better basic understanding of the printing process.
An STL file describes a shape you want to print, but it does not have all the information needed to actually print the object. In order to actually print the file, you need to know things like what material you will use (which will determine temperatures), what the capabilities of the machine are (how fast you can go), how much vertical detail is important to retain (layer thickness vs print time trade-off), and how strong the piece needs to be (trade-off between infill + wall thickness vs print time + material costs). You also need to specify things like how to orient the shape for best print results and what to do when there are steep overhangs or bridges.
To get this information, you must slice the STL (or OBJ or 3DS) file.
There are a number of different software packages available to do slicing, many of them freely available: Cura and slic3r come to mind. Makerbot also has their own slicer. I know you can download and install Cura on a Mac.
The output of the slicer is usually a .gcode file, and I would expect your Makerbots to be able to handle gcode files that were produced with the appropriate options. In fact, I strongly suspect the ".makerbot" file mentioned in your comment is actually a gcode file in disguise.
Why does this matter?
Print jobs can take hours and even days, and they tend to completely take over the computer while printing. No one wants to leave their laptop sitting next to a printer overnight, not able to do anything else. Newer printers will also have features like automatic resume from power loss, filament out detection, are more, that a are less likely to function properly when printing from a computer.
There's just too much that can go wrong while printing via computer, such that you're pretty much always better off going with the SD card or USB option.*
In other words, printing directly from your main computer is waaaaay down the list. It's not the first, second, or even third of fourth option as the best way to do this.

* A dedicated print station can work well, when setup properly, and people often use OctoPrint installed on a Raspberri Pi in this way. However, this also implies a high-end laptop is complete overkill for the task.

You can use Simplify3D to slice your .STL files into .X3G needed for the Makerbot. You can either connect to the printer via USB or export the .X3G file to an SD card for use in the printer. Hope this helps!


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How do I make the layers stick together more and warp less?
I have a Chiron from Anycubic and I have had some leveling issues in the last few weeks, however, I believe that I have sorted that. The layers attached to the base plate or the raft now come out very weird and I am uncertain why. I heard that this is caused by the extruder being too cold but I have turned up the temperature and nothing has changed. Could someone please help with this because I have a feeling this is the reason the prints are being warped slightly but enough to not fit together?
I am very new to all this and I have no one to help me with this, if you could help I would be very grateful.

My bed temperature is set to 70 °C and the speed is 50 mm/s. I manually leveled it afer the self leveling didn't work, the image shows the top layer of a very bad failed print that had the same settings as my other ones but this one specifically was worse. I use PLA and have the extruder set to a temp of 210 °C most of the time. I now have the base set to 80 °C due to when its lower, adhesion doesn't take place for some reason. There are no large overhangs on my models but it can comfortably do a 70ish degree angle with no major flaw. The extruder height is set to 2 mm due to some massive leveling issues I had before.

Welcome to 3DPrinting.SE! Please add a photo so that we can see what might be the problem, could be adhesion, too much cooling or a too large of an initial gap, now it is guesswork. ALso add a little bit more information, what material are you printing, what are the temperatures, speeds, etc.

Your description sounds like a 1st layer issue, especially since it is unaffected by extrusion temperature.  Besides a photo printing details such as material of your filament makes a difference in how to approach this.  The characteristics of your bed, such as temperature and anything to promote adhesion is important.

I could be too cold of the print bed. What temperature is your print bed set to?

@GuyTurner What's your Print material and the extruder temperature? What's the layer height? Are that unsupported overhangs?

@GuyTurner We really like to help out! Please add additional information, else this question might get closed (without enough information it would become speculation, as can be sen in the comments above). We would like to see the STL to confirm if there are overhangs, see an image of the first layer (initial layer height might be useful too), so flip the object around, need the extrusion temperature and the material. E.g. 70 °C bed temp. for PLA is a little high, but okay for PETG.

how do i add more images?, i have an image of a raft being printed.

Not sure what the other answers are talking about. From the picture, your nozzle is just way too far from the bed and the extruded material is just barely making contact. Adjust it so that, when moved to position Z=0.2, there is exactly 0.2 mm between the nozzle tip and the bed. Then fine-tune with single-layer test prints.
Having the nozzle way too far from the bed is probably why you've found a need to jack your bed temperature up so high. Don't do that! 80 °C bed is not usable at all for PLA; it will keep the first 5-10 mm of the print above its glass transition temperature permanently (for the duration of the print), precluding any hope of it holding a proper shape. 60 °C is the absolute max you should ever use for PLA, and even that's too high to avoid warping. If your nozzle distance is right and you're using a textured (e.g. Buildtak or generic clone) build surface, PLA should adhere to a cold bed (not heated at all). Without that you probably need 45-55 °C.

What software do you use? Your nozzle diameter seems to be selected incorrectly or you have a slightly enlarged nozzle. Buy an unused nozzle and make your bed adjustments again.
Select correct a nozzle diameter (such as 0.4 mm, 0.6 mm) and slice your print again. For PLA, I suggest using 200-215 °C for better layer adhesion and using the fan to make prints look better.

That is an over extrusion and temp related issue, based on your picture. But to answer your question, make your layer height less and slow down your speed in the first 10 layers.

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What filaments are appropriate for a case that will contain mains voltage wiring?
I have some relay boards which I want to build into a case for my Pi.  The relays are GPIO controlled and will turn on/off things like a 12 volt DC light, and the 240 volt 50 hertz AC printer itself.  The relays are rated for these levels and current draws.
However I would prefer to put the pi and its relays inside a case.  No commercial case exists to neatly hold the relays, so I have to design and print something.

What filaments can and can't be used to encase mains voltages?
What other considerations should be accounted for - minimum thickness?

Any filament except made-to-be-conductive metal infused filaments should be capable of acting as a suitable insulator, but you'll also want to consider things like failure modes under overheating, mechanical damage, whether it might be subject to spills of conductive fluids, etc. These are not so much a matter of filament choice as structural design and safety design on the electrical level (proper fuses, etc.), and may involve compliance with electrical code. I think those questions are outside the scope of 3D Printing SE, but would be appropriate on a sister site like DIY or Electronics.
From the 3D printing side, you might want to avoid PLA unless you can guarantee shutoff if anything exeeds about 55˚C, since you'll quickly get warping and loss of structural integrity past that. Although I do have an under-hood automotive part in PLA (wiper fluid connector) that's held up fine for a few years now. PETG or ABS/ASA would probably be preferable.

Thank you - sounds reasonable.   I only have PLA right now, and have never tried printing anything else.  This could be the motivation, and the PLA one can be a draught print.

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Fixing stringing within <80% flow print out is weak
Here are the details:

Creality CR 10-S5
BLTouch leveling sensor
Micro Swiss Direct Drive filament upgrade kit
Bed is 66 °C.

I tried dozens of temperatures starting at 205 °C and going all the way down to 180 °C pretty much 1 °C at a time. The present temperature of 188 °C seems to generate a higher stickiness to the bed than other temperatures.
I have also adjusted the flow rate down to 47% and that, although it did help with the stringing, didn't fix it completely and made the whole print super weak.  I have discovered going below 80% is structurally a bad idea.  I wouldn't mind having it at 90% either.
I am trying different retraction speeds and distances now currently testing 5 mm and 70 mm/s retraction.  Previously I tried 4 mm with 60 mm/s and it didn't help.
Using a lower filament flow rate (about <60%) did prevent it from going all the way across at approx 50 mm/s, but alas <60% is too weak structurally. And didn't solve it completely.  The tips had a Y-shaped split top on both sides with the one side of the Y being straight as it is part of the tower.
Any suggestions to rid me of this are welcome.  Reminder flow rate below 80% is too weak, and 188 °C is preferred.

The picture looks like classic Cura misbehavior - it's skipping retractions that need to happen because it's done "too many" already. You should be able to confirm this by looking at the gcode in an analyzer that shows retractions or watching the print. Set "Minimum Extrusion Distance Window" to 0 to fix the problem.
You should not be reducing flow at all, and certainly not by more than a few percent. Put it back to 100%.

Yes, that's the problem with Cura - it has a lot of settings with wrong defaults that most users don't even know exist... but once you configure it well, it does a great job.

Do you have any other settings suggestions I should watch out for?

Combing might be such a setting.

Yeah, in my opinion "Max Comb Distance With No Retract" should be set to a very low value just large enough to make it so moves between successive lines of top/bottom fill don't need retraction - something like 0.8 - 1.2 mm. This in turn kinda 'requires' turning on "Zig Zaggify Infill" unless you have really high speed retractions.


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What is this stepper motor connector called?
I'm struggling to find the name of a connector I just broke, so I can order a new one.
It's a six pin nylon terminal, that plugs into a set of header pins on a stepper motor.
What do I search for to find these?! Also, how would I go about finding something like this in the future? I seem to struggle to find connectors.

Adding a photo from another angle would help, and a photo of the socket on the stepper motor. Is it single row (1x6)? Also the size/dimensions, pitch of pins? Is there a locking mechanism on the other side..? [Edit] your question and update. Is the plastic housing actually broken, or you just need to replace the one burnt out pin?

Where is it from on your printer?  What model of printer?

It's essential to have both sides of a pin connector and some measurements - that way it is much easier to pin the pins down

Short answer: It's probably 6 pin JST PH
Long answer:
Without seeing the socket, it's hard to say for sure, however most Nema 17 stepper motors use 6 pin JST PH connectors with 2.0mm pitch on the motor side. Many control boards use JST XH connectors with 2.5mm pitch on the board side. The two are not compatible with each other due to a difference in pitch and the locking mechanism.
Looking at the sockets there is a clear visual difference: PH has a wide cutout while XH has two slots.

PH vs XH

The difference on the plug side is more subtle. XH has small hooks that grab onto the slots while PH has not.
There's a good reference at mattmillan.com which helps to identify different types of JST connectors.
EDIT: Usually the easiest and the cheapest option is to buy a pre-made stepper motor cable that fits your control board. However if it's not available in a length you need or re-wiring is hard, you will need connectors and a crimp tool with jaws specifically made for these types of connectors. The cheapest option is probably to borrow one if you can, these can cost a pretty penny.
Answering the second part of your question is tricky. Searching through parts catalogs is too time consuming. Using google image search or google lens to search with images taken from multiple angles is a good start to narrow it down but does not guarantee success.

No. They’re the Chinese knockoffs of the genuine JST connectors, called “XH2.54,” “general JST connectors,” or something. They have different dimensions than JST’s, and the genuine JST connectors are never used for most, if not all, of the stepper motors on the market.

In an attempt to salvage my (sadly) previously incorrect answer (at the bottom), and to add to anttix's superlative answer, here is a quote from Stepper cable for MKS Boards pinout, which clearly shows the difference - locking and non-locking, and pitch difference (note the thickness of the plastic between each individual pin socket) - in the two plugs:

This pinout information will help you to use our 1 meter stepper
cables correctly. Cable was made to be compatible with 6-pin JST
connectors on NEMA 17 stepper on one side and 4-pin JST connector on
other side. These cables are compatible with MKS BASE and MKS Gen
boards that we sell in our store.

For compatibility with Anet board you will need to swap 2 wires - RED
and BLUE on the 4 pin board side connector.

Whilst they aren't labeled PH and XH, it is pretty safe to assume that:

For the control board, the 4 pin female connector on the left is the XH, and;
For the stepper motor, the 6 pin female connector on the right is PH.

The mattmillan.com link in anttix's answer, whilst informative, unfortunately doesn't show both sides of the 4 or 6 pin connector.

For the sake of completeness, but at the risk of going off-topic, the connector to the printer controller board is often a DuPont, and not a JST, particularly in, but not limited to, Arduino (Atmel/AVR based) boards.
From the same website, this page Stepper cable for RAMPS pinout, shows the DuPont connector to the control board and the JST-PH-6P connector to the stepper motor (I've not fixed the typos in the quoted text):

This pinout information will help you to use our 1 meter stepper
cables correctly. Cable was made to be compatible with 6-pin JST
connectors on NEMA 17 stepper on one side and RAMPS board connector
(also called dupont connector) on other side. Main feature of RAMPS
stepper header and this cable is that you can reverse stepper
direction by turning connector on RAMPS 180 degree.
This cable is aslo compatible with CNC V3 shields for Arduino UNO and
other electronic boards for 3D Printers and CNC control. Please
observe the following piut diagram to make sure that your particular
electronic board is compatible.

Note: I'm not promoting this particular website, it just so happens that they have the best comparison photos.

Maybe It is most likely not... JST XH 2.54 6 pin female

and the reverse side, showing the locking, with the male PCB connector

Stepper motor cables normally use JST-PH connectors at the motor end, and JST-XH connectors at the board end, so the connector in the OP's image is a JST-PH-6P.  Anttix's answer is correct.

Yep, I was close but not close enough - I've updated my answer... :-) The connector code, no one has actually mentioned that yet. You should put it in a (short) answer.

@Mick The board end depends on the board you use, see e.g. https://ae01.alicdn.com/kf/He07d3704b22f4b429538c9d7e7d6a040r.jpg, some boards use DuPont (left magnification) others use JST-XH, (right magnification). Of the 10 controller boards I have, only one uses the XH at the board end, so I wouldn't say that that is the most common ;-)   (I guess you already imply that with normally... ).

Funnily enough I was going to add that DuPont is often used on the board end, like on RAMPS boards, but I'd got bored of typing at that point... updated answer again. However, we are veering off-topic a bit (mission creep) as the OP was only asking about the stepper motor end.

authors: Константин Ван


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What is the largest file (in terms of storage space\mb) that can be printed on an Elegoo Saturn?
In terms of Mb, rather than volume, what is the largest file size that the Elegoo Saturn 3D printer is capable of handling in a single print?
How is this limit determined, for example, is it due to a limit on the board, or in the Chitubox file format, or in some other way?

Not an Elegoo Saturn, but an Anycubic printer is my device. I've noted that each layer is loaded from the flash drive moments prior to the burn/flash/print. I suspect this method is used in many printers.
If you consider that even a large LCD panel requires only to present an open path for UV light or a closed path for each pixel, the amount of data required for a full printed layer or a fully empty layer is quite small in terms of bytes.
Non-monochrome LCD panels would use more data, as each pixel is defined in three colors (or none) compared to monochrome (on/off).
I believe that my printer uses the Chitubox board system, making the similarities to yours a valid comparison.
Your limitations would be based on the size of the medium containing the file as well as the physical size of the print.

And how would I calculate that in MB?

The most complex data pattern would be incidentally a checkerboard in a bitmap format (jpg), because each pixel is defined separately as it is not the same as the neighbor. Datawise, there is no difference in the picture file if it is shown on monochrome or non-monochrome panel. It is the display driver that turns it into the display's usage format of signals.


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Any filaments sun-safe and watertight?
Due to the surprisingly high cost, including shipping, of large water tanks (say, 100 gallons), I'm evaluating the possibility of creating one via 3d printing. (The pieces would of course have to be printed in chunks and fused together in a durable and watertight fashion-- I'm assuming for now that this can be done. It seems like a separate question, but feel free to address it in the comments.)
The question at hand is: is there any filament suitable for the task? The container needs to be able to sit out in the sun year-round without becoming nonfunctional.
The resources I've been reading (linked below) are suggesting PLA filament for small kitchenware items, but from what I've heard, that tends to degrade pretty quickly in the sun.
Are any filaments suitable for this?
https://www.instructables.com/3D-Printing-Make-Water-Tight-and-Air-Tight-Contain/
https://all3dp.com/2/waterproof-3d-print-pla/
https://all3dp.com/weekend-project-how-to-3d-print-watertight-and-airtight-containers/

A hundred gallons is pretty big -- about 14 cubic feet, or three times the volume of a common outdoor trash can,.  Even a pretty large FDM printer isn't going to print that in one piece, and if it's assembled from small pieces, you've got more leaks to worry about than through the printed parts.

Indeed 3D printing makes no sense for this. There are various decent ways you could fabricate your own such tanks though, from materials readily available at a hardware/home improvement type store.

You won't just need a watertight material for that, you'd need a watertight glue as well. And a lot of it too, for 100 gallons. With such an amount of water, I'd start worrying just a bit about waterpressure too. 100 gallons of water weighs about 1000 pounds.

I was thinking of using a heat-fusion method (think welding) rather than glue.

Not necessarily glue. Could be gaskets and bolts, or heat or ultrasonic welding, or acetone welding with suitable plastics, etc. But it still seems incredibly difficult, time-inefficient, and cost-inefficient.

The overall concept seems flawed, but for the joining part, ABS welds up nicely with an acetone/ABS mixture which can be tailored desired viscosity. I've assembled a nearly 1.5 m R/C boat of 40-50 printed parts. Strong and watertight "welds" were accomplished with ABS/acetone slurry about as thick as mustard/ketchup condiments. Also, size wise, consider the size of a typical 55 gallon drum. Nearly double that will be huge! I'd suggest inflatable tanks as an alternative. US$200 or less for Banks Outdoors Wild Water Bladders, 100 US gal.

i would not print for a large tank.  especially if i only need a few.  mold, form, seal, and coat.  maybe i'm leaning too far into a composite rather than 3d printed solution for this...

I've had PLA sit outside for 3y and it only got a little brittle.  I've also done friction welding with some success.  But unless you need a tank with a very strange shape, welding pre-made flat panels together or a bladder like solution would be better.

The Water-tightness part is already answered, the engineering problem makes this infeasible. In fact, it would be cheaper and faster to buy stainless sheet metal and weld the tank on the target place rather than to laminate a plastic container.

Watertight is hard to do with fdm printing . Lots of voids and pinholes. People have trouble with their vases holding water, and that’s one piece, not a patchwork or little parts.


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Can I put a glass plate in a Replicator+?
I have been reading that glass plates are really good, and the bed plates with the Makerbot Replicator+ are all not so good (I have had curling issues).
So here's the thing: thus far I've been able to cut the curling down by a) putting down a layer of gaffer tape, this seems to work well, and b) some Aqua Net which also seemed to work pretty well too at least so far (fingers crossed on latest print). I also found that simply putting a plastic bin on top of the Replicator + and using paper sheets (basically a huge pad with post-it strips on the top that I cut up) seems to do a reasonable job of keeping the temperature even -- the Z18 I use never seems to have curling problems and I suspect that temperature constancy is a huge factor.
Anyhow, I wondered what would happen if I tried to put a glass plate on top of the bed. I am assuming that I'd have to set the Z offset to like, a whole 4 mm or something crazy and that I'd probably end up with a printer crushing the extruder against a hard surface and all kinds of terrible things would ensue.
To be clear, I was thinking, get a sheet of tempered glass, clip it onto the build plate with like, binder clips or something. Replicator + build plates aren't heated, so I figured at the very least I ran the risk of having an extruder shoved forcefully into a glass plate which then proceeds to break in half.
So thoughts? Is putting a glass sheet down a really stupid idea? Like crazy stupid? It's not like I have a super duper urgent problem here, but I was curious.

Yes, you can add a sheet of glass to virtually any 3D printer.
But, having a heated bed is pretty essential to printing on glass. Although it is possible to use a glass bed on an unheated 3D printer, it isn't recommended to do that as you'll be running into issues with adhesion.
Glass beds work best when you apply heat and an adhesive like glue stick, hairspray (both are pretty obsolete nowadays) or preferable dedicated print adhesion sprays (3DLAC, DimaFix, MagicGoo, etc...).
Glass, when heated will provide:

A very flat surface (aids in leveling)
A very flat and shiny/mirror finish bottom layer (great when gluing halves together)
A means to take out the build surface with the print to cool elsewhere (when the glass cools, the prints usually dislodges itself due to differences in temperature expansion)
A means to quickly change the build surface to start a next print on a new sheet of glass
A surface that can easily be cleaned with common household products (glass does provide enough resistance against more aggressive cleaning solutions as well)

Thanks, this explains a lot and answers the question I had -- is a heated bed essential? -- because so many discussions of it seem to assume you have one, or that you don't need to say whether a heated bed is essential or not.

@Jesse It depends on the materials you print, PLA and PETG can be printed on an unheated bed surface. But printing it on glass successfully without heat would require to put down tape on the glass. That is pretty counter productive. The "sticky" bed adhesion solutions also work better with heat.


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Do print issues (extrusion, blockage, etc...) become less of a problem with more expensive printers?
I own an Ender 3, it's about 3 years old and the issues I have with extrusion, leaking and filament blockage are monstrous.
Examples of problems like this are filament flow issues, filament blockage, and filament leaking out of the sides.
Problems like this take all day to fix, and in the end, they are never really fixed. Everything is so overbearingly finicky.
Not only that, but it seems one of its parts breaks down about every week (this may just be due to its age but I thought I would note it.)
It seems I run into the exact same problems every single time I 3D print. Nothing ever seems to go right. I am getting really tired of it, and I'm wondering if these kinds of problems aren't so frequent/ as big of a deal with more expensive (better) 3D printers, or if this is just normal.

I have a 3yo ender3 as well and it doesn't have any of these problems.  But then maybe you print more than I do and yours is more worn.  Or maybe you buy cheap filament with debris in it that clogs your nozzle and stresses the rest of the printer.  Or maybe yours is actually ok and just needs some tightening.  Or maybe I got lucky and got a good printer and Ender's QC is random.

The issues you've hit (like filament "leaking") should not happen even on a cheap printer, and probably indicate you did something wrong (like not tightening the nozzle). There are lots of recurring problems with these types of machines that aren't user error, like play in undriven side of gantry, inconsistent extrusion from low extruder quality, etc. but the things you're hitting should not happen.

No not at all. The only way to eliminate issues is to practice and break things and learning how to fix it. I have 2 CR-10s, 1 CR-10S5, 1 CR-10 MINI, and 2 Anycubic Photons. They are all heavily modified, and the one thing i learned is that modifications only add to the problems

I got solved the most problems with my Prusa Mini after a better extruder from Bondtech (Extruder for Prusa Mini or Mini+). Because it has double gear it has enough power to press the filament through the nozzle. Another problem was the filament I ordered. It always got stuck in the Bowden tube because it got too thick. For just one dollar more I got filament that is much more accurate in the diameter and so it never got stuck.

Thank you for the update

I use a German RepRap printer, which is very expensive compared to many of the printers in the questions on this list. I still see similar printing issues on a RepRap to other printers. The settings often control the issues. The RepRap however has a much larger print area than most of the printers referred to on this list.

I've seem commercial stratsys printers with issues like this, where you have to call a service tech to fix them.

What is a RipRap printer? Please provide a link.

https://www.germanreprap.com/printer/x400EN.aspx

More expensive printers from reputable brands generally go hand in hand with better quality, but, there are exceptions. Some more expensive printers are just more expensive and do not offer a higher quality. I'm not going into the details of which brands these are.
I have experience with cheap, self-built and high-end printers and experience that even the higher end machines can have problems. Although the high-end printers generally have better engineered parts and better quality parts (e.g. like branded bearings, good steel, better hot ends) it is unlikely you run into failures more often, but failures do happen. E.g. recently I had a fine thread of filament wedged into the hot end cooling fan of an Ultimaker to fail printing PLA as the hot end becomes too hot and waisted a core on a PETG print that wrapped around the core.
One thing is for sure, when you do run into problems on expensive printers, it is generally also more expensive to fix it.

It would be highly dependant on the printer itself. For example, the Ender 5 is technically a more expensive printer than the Ender 3, but its hot end etc are functionally equivalent for the most part as the price difference is largely due to the large build volume and the Z axis being on the bed rather than the extruder.
Other higher grade printers, such as the Bambu range are significantly more expensive and have higher grade extruders and hot ends, but they can push the hardware much closer to its physical limitations, and so can create more problems.
Unless you are comparing differences between high and low end in the hundreds of dollars with very low end units and mid range units, the biggest single factor is likely to be how the printer is used and how it is maintained.
In some instances, problems may be more likely down to cheap filament, or filament with a high moisture content. Lower end printers may be more susceptible to these kind of issues.

Get a real E3D nozzle/extruder and  90 % of the problems disappear. The problem with cheap printers is that they use copies that are poorly build and low quality materials. After that if you want to improve even more you got to get a dual gear system for your extruder motor or a good gear and a body that you can adjust the tension in small steps.
Besides that, just check if your steppers are well calibrated and do a proper extrusion test


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Can’t get a proper first layer on my Ender 3 pro
I’ve been trying to level my bed for close to a week now and I don’t know what I’m doing wrong. I thought buying new springs and a glass bed would fix the problem, but it didn’t really help. I either have to raise the bed so high that almost no filament comes out or so low that there’s no adhesion.
On the attached photo there’s my last attempt. What should I do to fix those tears which run along the edge of the entire print


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Can't 'tune' out my problem, please help!
Alright, long story but I want to provide as much detail as possible:
I have a heavily modded Ender 3 Pro.  Mods include:

Metal Extruder
Capricorn PTFE tube
Glass bed with improved leveling nuts
BLTouch
LED strip
Dual Z-axis motors with the recent addition of BTT E3 RRF control board (and IDEX module so that it could do G34 auto-align) (most recent additions)

I'm using Overture Brand white PLA and for the first print that messed up (pic below), I was using the default "generic PLA" Cura settings for an Ender 3 pro.
The problem:
Anyhow, it caused this kind of print:

There are a few angles where it actually looks pretty good.  The hull is fairly smooth, the first layer went down well, the roofs and bridging look tolerable, but as you can see, especially around the "pillars" it looks I don't know... under-extruded?  Like the lines don't connect very strongly.  In fact, it might be hard to tell from this photo but the bottom actually ripped off when I took it off the plate, mostly due to weak connections between each layer.
What I've tried:
I pretty much went step by step through Teaching Tech's calibration guide.

I started by getting out my bubble level and 90-degree gauge and just making sure the frame/bed/everything was level and perpendicular to each other and everything.
I did the E-steps calibration until I reliably got 100 mm when I asked for 100 mm
My first layer had never been a problem (especially with BLTouch and glass bed), so I skipped that step.
I did the baseline print.  My first one looked like the top of the cube had some under extrusion (you can see through it if you look closely in this photo

I did the slicer flow calibration and actually it came out a little tiny bit too big (which would indicate I need to turn down the flow), but as Teaching Tech mentioned at the bottom of the page, you can't always trust that so I didn't end up making any changes to flow.

Worth pointing out, in this photo of the Slicer Flow calibration cube, you can see some weird holes where the nozzle would be kinda late starting a line.

The stepper motor driver current thing confuses me but I had previously set the current of both Z-axis' to the values I've seen in several YouTube videos, including Aurora.tech's channel where she covered the same BTT IDEX board and dual Z's.
I did the temperature tuning and it seems like for this PLA 210 °C seems to work well.
At this point I felt like retraction tuning was the problem and would fix everything, but with the default speeds in Teaching Tech's sample print, distances from 0-8 mm didn't seem to do anything differently in this print:

I never ended up doing the acceleration tuning
For the linear advance, I changed the k value to 0.4
I don't have a dial gauge to do the XYZ steps calibration

Long story short, with those few changes I redid the calibration cube and the benchy and they look maybe 5% better but still weird.
My Z-axis squeaks sometimes when moving through a spot 5-10 mm off the bed, so I lubricated them according to the guide here, but I did that prior to that second benchy so it didn't seem to solve it.
After I first posted this, I decided to dive deeper into that squeaky Z-axis.  I triple, super-duper checked that both Z threaded rods were parallel to each other and neither was warped/curved/etc...  They seem fine.  I lubricated them both a bit more and using G-code told the printer to jog the Z-axis up and down the length of the rods about 20ish times.   The squeak did eventually go away so I printed another benchy.  No dice.  Still looks bad.
Per Criggie's answer, I disabled the steppers and moved the axes around to see if they moved smoothly.  Both X and Y move great with steppers disabled and then are pretty firm normally.  Z is pretty stiff no matter what but that may be intentional.  I previously had problems with my Z-axis falling down when prints were over so I installed anti-backlash nuts and with two anti-backlash nuts (one on each rod) I'm not surprised it doesn't want to fall.  But again, when I just tell it to move, it moves very smoothly.
For instance, I just got out my micrometer and measured the Z movement.  I told it to move 100 mm up using OctoPrint and measured the actual movement.  Seemed to be 100 on the dot.
I have a BTT filament sensor in the filament path prior to the extruder.  I noticed it provided a little friction and I was concerned it was making it hard for the extruder to pull the filament.  I removed it, but no improvement in print quality.
One other strange thing I've noticed is the benchy always looks bad in the same spot (the pillars).  Makes me wonder WHY it's always that exact spot, not randomly all over.
It's got to have something to do with under-extrusion or flow.  I think I ruled out the Z-axis.  I made a "tall" benchy by modifying the benchy file to have a platform underneath it.  This bumped it up a few cm and the problem still happened in the same spot on the pillars of the benchy (which is now in a completely different spot on the Z.
Also, given the "flow" preview in Cura:

That circled low flow area is where it always messes up.
So now to figure out why it's got low flow.  Again, I calibrated the E-steps and it seems to be accurate.  I've also printed benchy's where I told Cura to have 110% flow just to check.  The last one I attempted didn't just fail, it failed big time and became a blob at that same spot.
I wonder if the extruder gear is worn and slipping and/or the Capricorn PTFE tube is too restrictive for the "budget" filament brand I'm using that might have trouble sliding through it.  I have replacement steel extruder gears showing up Tuesday, will update my question then.

Next time forget the bubble level! ;-) Level the printer to the printer axes, not to gravity! You clearly have an under-extrusion problem, I wonder how the 100 mm is being determined. If in free air, this may be quite different from "at height" which might add more backpressure causing you extruder to skip.

@0scar  Oh I understand.  When I say I used the bubble level (I did), I just mean that I checked in a couple places that they had the same angle/tilt/level as a corresponding piece.  I.e. they were parallel.  I know that it doesn't necessarily have to be level in terms of gravity.   I also used a right angle gauge etc.. And as far as the 100mm, that was just in free air, what do you mean by "at height"?

When the nozzle is close to the bed when extruding, there is backpressure from squeezing the filament into the set height (layer height + initial gap). This can cause a different length than 100 mm, but it should not, it means that the filament/extruder is skipping. You clearly are under-extruding, you need to fix that. Could be that your retraction is also not optimal, but you have looked into that. How did you determine the LA value?

@0scar For the linear advance I used the linear advance calibration guide on teaching tech's website.  It printed the grid from here: https://marlinfw.org/tools/lin_advance/k-factor.html and the 0.4 line looked the best.
My understanding of retraction makes me think its that, but like I said, distances from 0 to 8mm all kinda looked the same, I must be missing something.
I didn't notice the extruder skipping/grinding/causing dust or anything.... but I'll watch it like a hawk tonight and report back.

@0scar Added some notes above about the stepper movement.  As far as the under extrusion I haven't got to an answer yet but I have more info:
I watched it super carefully last night as I printed another benchy.  Did not notice any filament grinding and/or slipping.  I DID notice that my btt filament sensor wasn't as smooth as it should be to pull filament through, so I took that off to free up the path.  Was convinced that would solve it but no dice.  Its also strange that the rest of the print does pretty well except for those pillars (happened again).

Excessive force of the filament from the spool (entangled, high friction, etc.) also causes under-extrusion. You really need to focus on the filament and the extruder, the Bowden tube, everything between the nozzle and where the spool is located.

Need to highlight @0scar 's "retraction is not optimal" idea again. The Cura defaults are for a bowden printer, something like 6.5 mm. If you have a direct hot end that will be waaaaay too much. You usually want it closer to 1.5 mm.

@JoelCoehoorn  Totally agreed that from my understanding of retraction, it seems like that could lead to the problem.  That being said, as you can see in my notes above, I can't figure out how to fix it.  I've done a retraction tower with everything from 0-8mm options and they all kinda look the same.   I'm on a bowden setup and I think I ended up leaving it at 6mm, but again.... doesn't seem to do anything.

If this is your reference for a calibration cube, please read my comment. You're spot on with the cube makers ;-) , but as in that comment, that image is not correct. What strikes me is the re-occurring pattern like it is in sync with the threaded rods pitch? Maybe you could decouple the spool and feed the extruder a pre-cut length + 1 m of what you would need for the cube, print the cube and measure what is left minus 1 m and compare that to the calculated by the slicer.

It was a worn extruder gear.  I didn’t think it was THAT worn, and when I loosened it a bit and slid it a few mm so that the gear hit the filament in a fresh spot it didn’t improve.  But new stainless steel gears showed up today and when I installed one it worked perfect. Same file/settings/gcode that had failed several times previously when testing other things

I see positional errors in X and Y, but Z looks okay.
That suggests one or both of your belts is stretched, perhaps damaged, or maybe just loose.
Try engaging the stepper motors in the device's panel and push the head left/right or pull the bed toward/away from you.  They should both resist handforce, and you then feel like it needs to be pushed with full arm/shoulder force to move it (but don't actually force anything with that level !!)
There should be none/almost no play in X or Y with the steppers locked/engaged.
Then disable the stepper motors in the same menu, and both bed and head should slide with one finger's push.
This test does not work for Z but that axis seems fine in your benchy print.
Also check the condition of the drive/tension pulleys at either end of the belts.  There should be no powdered plastic from the cogs, nor rubbery bits from the belt.
I cannot see any over/under extrusion, so the extruder/drive is probably okay.

Thank you.  I'll triple check all this tonight when I get home.
That being said, I had disabled the steppers and moved everything around earlier in the evening before posting that question (not to check anything, just happened to) and it seemed to have fluid movement.  I'll purposefully examine it later.    Also worth pointing out I edited the question to fix some of the photo links.


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Clearing persistent partial clog after printing nylon
My Prusa i3 MK3S printer experienced a partial clog last time I was printing with nylon.
Although I've experienced clogs and partial clogs before, all the usual tricks I've tried have not worked this time; using an acupuncture needle to dislodge the blockage, running cleaning floss filament through at 285 °C, as well as numerous hot and cold pulls.
Despite all of the above, and being able to run some filament through the nozzle manually, as soon as I start to try and print, there is too much resistance for the extruder to force the filament through the nozzle and the Bondtech gears just grind up the filament instead of extruding it.
I've also removed the PTFE tube and checked that and it's in perfect condition.
Is there anything else I can try to try and clear the blockage? I'm highly reluctant to change the nozzle, as last time I did this, I bent the heatbreak despite following Prusa's instructions to the letter - the nozzle was just too seized in the heat block, I assume with degraded/encrusted filament.

I always used electric guitar strings. They are 0.05 mm smaller than the nozzle and because of the texture it scratches off any material that is stuck. Plus since it's not hard there's is almost no chance to damage the nozzle


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CR-6 SE rebooting at fixed moments in print
My printer seems to be responding poorly to some of the prints I provide it with. At a certain time, usually after at least half an hour.
For example, the print I tried today (twice) kept crashing somewhere after 52 minutes. Both times at the same spot. It would instantly reboot, ask to continue and even if I did it would crash again at the end of the backtracking.
A couple of things come to mind:

PSU/motherboard responding poorly to some set of actions. Doing the same actions again triggers the same problem.
Slicer producing illegal actions in some situations, causing the motherboard to panic.
Firmware being bugged, responding poorly in some edge cases.

Other prints work fine.
How would I go about finding what's causing the reboots?
As a workaround, I'd accept a method of finding out whether a specific print would have this behaviour (incl. looking at the resulting gcode if that helps), without having to waste an hour (or more) of time and material each time.
System:

CR-6 SE.
Recent Community Firmware.
Stock parts except for the cold-end extruder, that's switched out for an all-metal dual-gear.
Creality Slicer 4.8.2.

Note: I feel obligated to mention the printer is on an unearthed power socket (old building, only ground floor has a couple of earthed sockets). This might make parts of the system less forgiving than it would otherwise, but I'm not sure about that. Internal wiring of the printer (for as much as it's accessible) seems fine.

Turns out this is the behaviour of files that get corrupted. This has very little to do with the slicer and everything with how some SD cards are just intent on getting themselves a bad name.
In this case, the file was corrupted enough not to be readable on the machine that put the data on there. If the file can't be opened and made look readable by a normal text editor, it's probably corrupted and not worth trying to print. A quick scroll-through to check it's all there might be a good idea as well.


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When do you need a silicone sock? What problem does it solve?
I'm returning to 3d printing and there's all sorts of new things going on.  One of which is a silicone sock.  I suspect it's part of the engineering where you want to keep certain parts hot, and certain parts cold, and it assists with that, but I'm not sure.  Internet searches have been degrading, and have degraded a lot in the past year or so, so I can't find anything on the subject on how and why, just products.
When do you need a silicone sock?  What problem does it solve?
My Ender 3v2 came with one, but apparently previous generations did not.  My other printers do not have an option for them.

A silicone sock helps keep the heat from the hot end from radiating down onto the freshly-printed parts, which have a blower fan cooling them.
The sock also helps keep the hot end hot and away from that stream of room-temperature cooling air blowing at the part.
As such, the sock is a thermal isolator, helping to keep the hot bits hot and the cooler bits cool.

Additionally, silicone rubber is pretty good at not sticking to hot filament. If your print goes bad and produces "spaghetti" then the sock will mitigate how much plastic gets stuck to the hot end.

Are there certain heat blocks that are more or less susceptible to this problem?  FOr example copper vs aluminum.

Might want to add if your print goes bad and produces "spaghetti", the sock will mitigate how much plastic gets stuck to the hot end.

@YetAnotherRandomUser sorry, I don't have an answer for that.  Since the Ender came with one, there's no gain in removing it.

Good answer, one other benefit of the sock is less heat radiates up on the bottom of the cold end fins, helping a little with heat creep.

I experienced that the heater block can compensate an always-on part cooling fan very good, but I run into thermal runaway (9 out of 10 times) if the fan kicks in after N-layers. A silicon sock keeps the temperature of the block quite stable.


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What OEM is Inland PETG+?
I have a local Microcenter and got some cool orange PETG+.  I've never printed with PETG before, but this PETG+ stuff seems flexible and weak.  I printed a random part with some thin walls, and when I squeezed it, I broke the thin walls.  Interestingly, not across layer lines.  The same part in ASA (or ABS? I can't recall) is sufficiently strong and durable, and much less flexible.
I'm reprinting at 100% infill (the first one was 20%), but looking at the place that it broke, I don't see infill. It's ~2 mm thick there, so I'm pretty sure that it's solid.  I printed at 240 °C, and my reprint is going at 250 °C.
I'd like to check what this PETG+ stuff is better at than regular PETG, so I'd like to look at what the manufacturer has to say about it, and the rest of the internet. Who makes this?
We know that Inland PLA+ is made by eSun, and when I mentioned that to the local Microcenter 3D printer expert, he said as much too.  Here's a reddit post speculating.
Product page

are you comfortable with the possible hydration of the filament. Of the many types of filament, nylon is severely hygroscopic, with PETG coming in close to the top. If you have a filament dryer or food dehydrator, a dozen hours in the heat may improve the results.

I've heard varying degrees of hydrophilia for this kind of filament from "dry it and print from a dry bed" to "store it in a drybox, but it will be fine".  The print looks amazing. I suspect that it's something to do with the part.  I printed another one at 100% infill, and it broke in the same spot, but then if I tried to bend the piece that broke off, it bent, it did not break.  It's breaking with layer lines and bending against it though.

I've had really bad experiences with wet PETG. The mechanism of failure is consistent with what OP experienced - water bubbles exploding during extrusion and creating perforations in the extrusion lines rather than just bad layer adhesion. Somehow PETG really likes to break along "perforations" - this also happens when you have skipping-type underextrusion in a layer.

I talked to the guy at the local Micro Center.  He said that Inland PETG+ was OEM'd by eSun, and that Inland PETG was OEM'd by Polymaker.


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Offline CAD software for beginners
I have used OpenSCAD to design a couple of basic things.  However, I'm incredibly frustrated by the current state of CAD software: it's all browser based, or requires an internet connection.  Or has a learning curve like a cliff.
Are there any offline, nonsubscription, no-account-needed CAD softwares meant for 3D printing enthusiasts that don't have a degree in CAD?
I've seen plenty of tutorials that make it all look easy, and the softwares I have tried just don't do anything.
OpenSCAD is good for blocky well defined shapes and things, but right now I want to make a simple design to hold up a dowel. I've tried Blender and can't figure out how to give a dimension. Same for Sketchup Make 2017. I can't find a useful button in FreeCAD. I've tried Fusion 360 a while ago, but I hear that it recently took a major turn for the worse.
I want to design some stuff without giving away my digital soul in the process.

I'm a fan of OpenSCAD but recognize the limitations within the program. Part of the feature bundle of OpenSCAD is the parametric aspect. If you want to aim in that direction and can handle a GUI type of CAD program, consider to check out SolveSpace. All images courtesy of linked site.

Additionally, there is a Tutorial link on the site with a series of lessons to assist the transition to the program. The image below is the introductory tutorial part creation.
It's heavily keyboard biased, but for each key shortcut, there's an icon/GUI button option. As with many CAD programs, using the keyboard can be faster than searching for a sometimes-indistinct icon for a specific operation.

It's just an opinion, but Fusion 360 hasn't necessarily taken a turn for the worse, especially at the free hobbyist level. Change can be difficult, especially for us more mature computer uses (IBM 5150, anyone?) and F360 has managed to relocate/hide a number of features. It's a matter of finding them, but that adds to the learning curve.

My understanding the licensing had change in F360, not the GUI.

I am currently using F360 under an academic license and I have not had any problems with it. Granted, I am teaching myself via YouTube vids and banging my head against the wall. I started using F360 just before the change and the program itself has not changed significantly.


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Low fidelity 3D printer for plastic waste
Is there such thing as a 3D printer with a very large diameter nozzle, that can make low fidelity, large and fast prints? I'm picturing a soft serve ice-cream machine on a gantry, with a hopper.  You feed it shredded plastic, and it prints bricks, or boards.

Yes these exist. 3D printers using pellets is not uncommon for industry, but for the user at home this might be a different question. Pellets are the pre-fabricate before it is extruded into filament (small balls/cylinders of plastic).

Random image showing a variety of pellets in different colors
There are even processes to turn used plastic into pellets, so if you combine it all this should be very doable. The problem is to get a consistent type of waste plastic to feed your machine. The size of the nozzle doesn't matter, as long as your shredding, compressing and heating process can keep up with the flow you need. It would be an excellent idea to get rid of plastic waste and turning these into building bricks e.g. for insulation of heat.

I've seen prototype printers printing PEEK from pallets having a nozzle (slot) diameter of several millimeters.

You can certainly get large nozzles, but the material for extrusion still needs to be consistent.  So any chunked plastic would have to be melted and that will produce an erratic flow at the extruder.
By reforming your shredded plastic into a consistent string of filament, then the printer has a steady supply of material to use.  There are already filament extruders for the small shop, but they're still expensive for the home user.  The main problems are getting consistent thickness of filament, and minimising contaminants.  Also colours tend to be lost and muddied.  These might be economical if you have a print farm and are consuming a spool a day on average.
On a large scale, there are "3d printers" that can place a special quick-drying concrete and produce small buildings as homes in a matter of days.  However they're fed a special mixture of smooth cement and accelerators to set the concrete ready for the next layer.


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My Ender 3 Pro power switch is stuck to on
Started up my Ender 3 today and the print killed halfway because my cat was messing with the cable to my octopi, but when I went to shut it off to reboot and the actual switch seems permanently on (as in stays on regardless of position). do I need a new PSU? and is this a known issue?

You might need to consider how to keep the cat off the printer.   I mean I find it hypnotic to just watch - a cat will want to get involved and mess up your print.  Some form of enclosure might be a good idea,

on my todo list already.

The mains switch is easily replaced - the part is widely available. Just make sure that the spade connectors go on securely and to the same positions as the old one.
Here's how the wires are connected in my Ender 3's mains input:

The IEC mains connector is on the right in the first image. You can see the yellow wire goes to the earth connection of the PSU. The black wire goes to the neutral connection of the PSU. The live input goes via a wire strip to one end of the fuse, the other end of the fuse is connected to the central pole of the switch, and the on-position of the switch is connected to the live connection of the PSU via the red wire which leaves the picture.
The switch is on the left in the first image, and at the bottom in the second image.

tiny issue i forgot what way the spades go........

@TristanAdams Hang on... I'll take a photo of my Ender 3's mains input.

now I just have to order the parts and install. and thanks your a life saver (I'd probably get zapped without your advice)


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3D scanner capabilities
Will a 3D scanner capture internal details within an enclosure?
I'm contemplating buying a 3D scanner, but they're pretty expensive so I'm looking for advice on whether they will actually be useful for the projects I have in mind. So with the picture below as an example, could I expect to generate a usable STL file by scanning this?

I've found that if you can buy the part you want, it is generally better to do so.  Assuming that is the item, it looks like a 38mm or 50mm flush mount box for holding electrical switch plates, and would be cheaper to buy from an electrical retailer than its cost in filament alone.  It would be made of ABS, I can see that printed on it.

@Criggie yeah... it's not just this particular part I have in mind, it just serves the purpose of illustrating complexity within an enclosure

If you require precise scanning capability, for the purpose of reverse engineering, a photogrammetric scanner may not provide that precision. As you've noted, many scanners are quite expensive and with higher precision comes higher expense. The professional grade scanners will provide resolution figures based on a sample size. For example, a particular scanner will advise for 1.0 mm for an object of 1 meter (example, not necessarily reality) and the resolution may be worse for a larger item.
Having a stationary object provides for a better result. Living beings tend to move, making it difficult to scan with any detail. Reflective objects may require a non-reflective coating (chalk paint) to remove detail-damaging specularities.
I have what is known as a structured light scanner (SLS). It calibrates by using a known pattern and projects varying light/dark patterns on the calibration panel. This calibration sequence is then used when the object is scanned. The distortion and light/dark changes are then converted into the 3D mesh, which is later converted to an appropriate object, such as .STL, .OBJ or other formats.
In the case of the object in the image, one would perform repeated scans while rotating the item on a turntable or similar work space. These are nested and processed by the software as noted above. With the walls, recesses and holes in the pictured item, it will be necessary to place the object in various orientations, by resting it on a flat side, or upside down. The software may automatically adjust the new scans, or may require point identification to begin the automatic sequence.
Unfortunately, these SLS devices are also not particularly inexpensive, but such a term is fairly subjective. From a hobbyist standpoint, it could be considered big bucks. For a prototyping operation or especially from a production environment, the cost may be a small portion of the budget.
David SLS is one such device. Amazon has a listing (unavailable) as does Walmart (out of stock) priced at US$2360. Not inexpensive, but not astronomical. The listing from Amazon specifies 0.1% of overall size. For a 150 mm wide object, that would mean 0.15 mm resolution.

Thanks, well outside my budget then, better to 3d draw the gadget.

A more budget solution is presented in

with lots of detail posted at https://www.jeffgeerling.com/blog/2021/modeling-my-grandpa-3d-photogrammetry
Essentially it's some fancy PC software to stitch together a lot of digital photos of an object, and produce something you can print.  The code used was COLMAP + OpenMVS and is explained in gratuitous detail in https://peterfalkingham.com/2018/04/01/colmap-openmvs-scripts-updated/

I know this is a link-heavy answer which is discouraged, but there's an inordinate amount of info posted, and is far too detailed to summarise here without losing important points.

interesting approach but too complicated for me I think. Maybe if was a person, but for parts it's probably easier to draw them, just need to get my head around my 3d software

Yes, a 3D scanner is capable of capturing internal details within an enclosure. However, the quality of the scan may depend on the specific model and settings used. It is always best to research and read reviews before making a purchase to ensure it will meet your needs. As for the picture you provided, it is possible to generate a usable STL file by scanning it with a 3D scanner.

Yes, 3D scanners can do that, provided that all surfaces are in sight of the scanner.
Within our company we scan complex turbomachinery parts (e.g. impellers) using a robotic arm with 3D scanner and a rotating platform to scan the whole surface of the parts to compare used parts to new parts and evaluate if they can be used for another maintenance interval.


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Drawing simple circle in G-code
I thought I am not bad at Google, but simply I am unable to find a G-code for doing circular motion for nozzle cleaning. It is possible to write a simple circular motion in G-code?

Marlin's g-code reference is so good that I don't Google for this kind off information anymore; I go rightly to it.

To draw a circle, you need to approximate the circle as a sufficient number of line segments. This requires computing or using a table of sine and cosine values for each angle step. Then you just emit a sequence of G1 commands.
Some printer firmware also supports arc drawing commands you could use instead in principle, but support is not widespread, and the quality of the results varies enough that I would not recommend trying to do it this way.

While many 3D printers support using G2 and G3 for circles and arcs, most people are not used to them because the STL files consist entirely of flat triangles (straight lines).
If you want a simple 2D circle, see the following for help:
https://marlinfw.org/docs/gcode/G002-G003.html
https://makezine.com/2016/10/24/get-to-know-your-cnc-how-to-read-g-code/
https://reprap.org/wiki/G-code#G2_.26_G3:_Controlled_Arc_Move
Note: it can take a while to get used to the I and J parameters.


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I3 Mega, PROBE_MANUALLY with ABL
I created some Marlin versions for Creality and Anycubic printers. Now I have a problem and want to ask if someone can help me, give some tips or something else.
Printer: i3 Mega Anycubic
I use the 2.0.bugfixes and took a configuration example from 2.0.8.1
The firmware works, but the movement/travel from XY is very slow when I go to the next probe_point.
Homing works great.
Only the probe_manually does not work.
Steps to Reproduce:

Try Disable Auto bed
set up XY_PROBE_FEEDRATE (100*60) higher
set HOMING_FEEDRATE_MM_M higher
disable AUTO_BED_LEVELING_BILINEAR

Nothing helps
It looks like the xy_probe_feedrate would not be interpreted...

Does this answer your question? Note that parameter names change over time SPEED now seems to be FEEDRATE, see Marlin/src/inc/SanityCheck.h.

@oscar Thank for your answer. I think it doesn't help, because i already use the new name "Feedrate" and not the old declaration "Speed". I hope i understand you.


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Large prints cracking
I'm trying to print large objects (around 1 meter squared) with polycarbonate pellets. The problem is sometimes the print cracks. It is not due to delamination as it is a shear crack across multiple layers. I know the ideal scenario is to have a heated enclosure but I cannot do that due to the size. Any suggestions?
I am using a robotic arm (KUKA KR360) with a custom extruder. That is why I can't build the enclosure. As for the temperature, they are 230 to 260 °C. Nozzle is 10 mm.

I like the idea of directed heat. I might try that.

You need to tell us what printer you are using, nozzle size and temps.

Printing polycarbonate requires a high end 3D printer that is suitable for the task.
From Simplify3d support we learn that:

... requires very high temperatures for printing and will exhibit layer separation if printed at too low of a temperature or with excessive cooling enabled. Polycarbonate is frequently best printed on a machine that has an enclosed build volume and is capable of handling high bed and extruder temperatures.

High temperatures and enclosed build volume are key to print polycarbonate without cracking or delamination.

Any suggestions?

Note that NASA has successfully printed ULTEM (even higher temperatures needed) using open source hardware. They have used infrared lamps directed at the build plate, this may be an option if a full enclosure is not possible. Also people seem to get good results with draft shields for printing ABS on non enclosed printers. Key is that a constant elevated temperature is created near the print, whether that works for such a large size remains to be seen. Best solution would be enclosing the printer.

Sounds like your problem is cooling, which would be mitigated by an enclosure to eliminate draughts and hold a higher air temperature.
I made an enclosure using parts-on-hand and some printed PLA joiners.  It doesn't have to be fancy or expensive to work well.
Details are at https://3dprinting.stackexchange.com/a/18406/12956
Next step is to sew some thermal "curtains" as sides and top.  As it is I simply hang some coats around the frame in the short term, and use a Pi camera inside to monitor the progress from remote.

Get a tent for growing smokey plants :)
Think about it, they can be of big sizes and maintain heat inside, reflective material on the inside.

The idea of using an enclosure has already been mentioned in the other answer provided. Please [edit] your answer to provide additional details with supporting documentation/links.


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Over-extruding on small layer heights (0.06 mm), but fine above 0.15 mm?
I re-assembled an i3 that used to be on a production line. It works OK when the layer height is set to 0.15 mm, but it over extrudes “A LOT” when used with a layer height like 0.06 mm.
At first I thought it was just “ANOTHER” random issue.
The same machine had:

burnt 5 V regulator on the Arduino Mega
burnt display (as a result of the above)
broken extruder stepper motor (would never extrude/retract the same amount, looked like re-assembled)
overheating A4988 drivers with Vref extremely high (above specs)
dual Z axis motors connected in parallel, requiring bigger drivers, but still using a single A4988
improperly assembled hotend that would clog constantly.
screw to tighten the material (it didn't use a spring, which I prefer since it's more lenient with the material diameter)

So I kept the RAMPS 1.4, and replaced/rewired everything else. Bought a 12 V PSU, installed a new display, added four DRV8825 modded for fast-decay configuration to replace the A4988, wired the dual Z axis in series, replaced the broken motor and everything looked finally OK.
But there is one single problem that remains:
picking any layer height below 0.15 mm causes issues.
Imagine printing with a 100 % over-extrussion setting. Pieces look too wide, and you can clearly see the nozzle is "inserted" into the 3D piece because there is way too much material. I can't print small pieces because they become "bloated" and I have to stop printing after about 2 mm of height (on the Z axis) since I'm afraid the nozzle will eventually get stuck inside all the extra material.
Things I checked (other than the new components from above):

X, Y and Z axis steps are properly calibrated
The extruder is calibrated and it always extrudes the correct length of material
Different steppings: 1/16 stepping when using the A4988 and 1/32 stepping with the new DRV8825.
Different slicers. Tried Ultimaker Cura and Slic3r (the original, not the Prusa version).

Any ideas on what may be the issue? I don't know what else to try.


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BLTouch collides with side of bed when starting print AFTER leveling
Okay, this one is a bit weird as everything else on the printer (for the most part at least...) is working perfectly. Some minor adjustments here and there are needed but this issue has shown up recently since adding a BLTouch.
After starting the print my printer regardless if I have it set up to wipe or not will them run the BLTouch (NOT the extruder, ONLY the BLTouch) into the side of the print bed. All of my offsets seem to be correct but for whatever reason, I can't seem to figure out what to correct to make this not run into the side of the bed as admittedly after the collision it prints fine! Any ideas?
(I have provided a video to give a better idea as to what exactly is going on as there are similar issues however they don't quite match my situation from what I've seen)

The problem is not after leveling, but during leveling when probing the first point of the mesh. As it fails to detect the trigger point, it skips further levelling steps. As the probe doesn't retract it is bound to cause a problem.
This could potentially be a non-genuine Antclabs touch probe, which are of lower quality than the original Antclabs BLTouch. The original BLTouch has a screw on top which might be present here also, you could try to adjust it for it to retract better on triggering (see this answer for some more information on the working of a touch sensor). The screw attracts the magnet on the top of the probe pin, getting the screw closer (clockwise) to increase the attraction and thus make it easier to attract it back up when retracting.
If the probe retracts in the middle of the bed, it should retract at every point on the bed. If it does not retract, there is something wrong with the sensor. You could insert an additional spacer (0.5 - 1 mm) between the mount and the probe to make a little more distance between the nozzle and the probe.

Could be the angle of the video, but make sure the frame is at 90° angles and the bed is as level as possible. Note that when using a sheet of glass, it generally is not required to use a touch sensor for scanning the surface, glass is flat. You could check with a ruler on its side. Basically, G29 can be skipped by taking it out of the start G-code, the sensor will than only be used in the middle of the bed to home Z.

I would note this is the genuine Creality BL touch so dunno about any issues there as the orignal bltouch I had catastrophic issues with oroginally I'll see about skiping G29 though and see if it solves my issue thanks


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Best way to put a serial number on a 3D print
I want to put in a date and serial number that would be difficult to erase or change. Is it better to print in the number or engrave it in with a laser engraver.
Material will be anti-bacterial PLA.
It will be on free masks donated to schools, I want to make sure we can identify them when they show up at the market or in shops.

I ended up laser engraving them, I tried printing them and it was too easy to remove the numbers

For this specific application, it may be better to think in terms of a Lot Number for each batch instead of individual serial numbers. This will still let you trace back an item for where it was originally allocated, and greatly simplify your processing.
Under this plan, you create the STL file for the basic part and before each printing batch open the base file in even a simple tool like MS 3D Builder or TinkerCAD to emboss your number and the date, re-slice, and print.
I actually recommend a deboss here, where the text is recessed into the piece instead of extended outward. In this way it will be more difficult to file away without damaging the part, and again, even the basic modelling tools can quickly customize an STL file in this way.
If you really need individual serial numbers, design the part with a basic recessed rectangular cutout and print these in bulk. Then print individual plates the exact size (very slightly smaller) than the cutout with the serial number and date debossed, and superglue the plates down.
Finally, be aware there's a limit to how small the text can be, based on the size of the nozzle and the capabilities of the printer, and you may find it difficult to print very small text.

It's plastic. Nothing is difficult to remove, but it could be difficult to remove without damaging the functionality of visual quality of the part. If you want to be really devious, you could embed the serial number in an inaccessible cavity inside the print that's not visible without breaking it open.
However, I wonder if it would make more sense to drop this. If you're worried about students (?) or educators (?) stealing and reselling these items, does having a way to trace and punish them really benefit anyone? Even before you consider the harms from doing so, isn't the effort spent tracing (and even the effort automating generation of STLs with each serial number and slicing each one to print individually, rather than using a single gcode job) greater than the value of the item you're worried about losing?

What type of masks are you talking about?

like this https://againstcovid19.cern/articles/cern-develops-washable-3d-printed-face-mask

Those are silicone masks produced from a printed mold, not printed masks. It was generally determined early on in the pandemic that hard plastic printed masks were not a viable health measure. They can't be made air tight or comfortable to face, and with gaps are less effective than regular cloth masks.

no idea, just posted the first one I got from google that had the filters. the mask my daughter found is 3d printed, I'd try and find it, but not relevant to the question

OK, well if you did want to do molds like in the thing you linked, that would be an added complication for the serial numbers, since you'd need a way to change out the number each time you used the mold. Anyway, the reason I asked what kind of mask is that I have no idea what a viable 3D printed mask would look like, and that affects how you might viably be able to put identifying information on it.

No molds, I have already purchased them a printer and the antibacterial pla, just waiting on shipping to this country. It's not my project

Have you considered using a barcode rather than text. It would be easier to print clearly as there are no curves, and would be machine readable.


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Factory reset needed!
I have just bought a Creality Ender 3 Pro. During setup, I think I must have applied an offset... The nozzle lifts up about 5 mm from the bed when starting to print.
I am reading that M502 resets to factory settings and M500 saves the settings. I have looked everywhere I can think of but am unable to find these files to download.
Can someone help me please? Where can I find these files?

What "files" are you talking about? If you mean the M502 and M500, those are commands that are sent to the printer. More info can be found at What is a printer console/terminal?.

This could potentially be closed as a duplicate of  What is a printer console/terminal?.

M502 and M500 are not files, they are G-code commands (well, they are actually M-codes, but don't worry about that)1.
To reset your printer to the factory default settings, simply connect a terminal and send M502.
If you are using Linux, see How to directly send G-code to printer from a Linux terminal?
See also M502 will reset all configurable settings to their "factory defaults", which settings are those?

1 Simply put: G-codes control movement; whereas M-codes control other functions (which aren't movements).


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Machined Aluminium Print Bed
I'm currently printing on a glass bed and it is warped in the centre of the bed. Not by much, but enough that my prints aren't the quality I want them out. My work around at the moment is to print on a raft.
I'm thinking if I was to replace the glass bed with a aluminium bed. I know this has been asked before, but the difference is I can get the aluminium plate machined at 65 °C. By doing this will it remove the potential for a warp completely? Or will it still have the potential to warp even being machined at 65 °C?

What type of aluminum, cast or rolled? Is it heat treated? 5-, 6- or 7000 series? What is the thickness, 3 or 6 mm?

Sounds like you got a bad plate.  Try buying a replacement before getting too deep into "make a new one"


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What is ABL or UBL? Is this the same?
When looking at Marlin firmware or reading on leveling of the printer bed the term ABL and UBL are frequently used.

What are ABL and UBL?
Are they the same?

What are ABL and UBL?

ABL stands for Automatic Bed Leveling
UBL stands for Unified Bed Leveling

Level the bed?
A level bed (twisting knobs under the bed), or a surface that is exactly followed by the nozzle is a prime requisite for 3D printing. Without a proper bed setup (not only level, but also the initial nozzle to bed surface gap; usually the paper thickness distance, but a feeler gauge will do a similar job), adhesion to the print surface might not be optimal and causes the print to get loose during printing or the first layer may not adhere at all.
A leveling solution
Over the years, 3D printing hardware and software has evolved to aid the 3D print operator. One such a solution is the use of a sensor (see e.g. Automatic Bed Leveling (ABL) with a sensor (BLTouch, inductive, capacitive), how does it work?). But a dedicated sensor it not a prime requisite, you can also do it manually.
ABL
Automatic bed leveling comes in many forms, the use of a sensor to sense the proximity of the build surface (inductive, capacitive, optical or through physical touching) enabled scanning of the build surface. In the Marlin firmware, more specific in the configuration.h file of the firmware (note this is a generic one, your printer might need adaptions!), the following on automatic bed leveling is to be found:

AUTO_BED_LEVELING_3POINT
Probe 3 arbitrary points on the bed (that aren't collinear)
You specify the XY coordinates of all 3 points.
The result is a single tilted plane. Best for a flat bed.

AUTO_BED_LEVELING_LINEAR
Probe several points in a grid.
You specify the rectangle and the density of sample points.
The result is a single tilted plane. Best for a flat bed.

AUTO_BED_LEVELING_BILINEAR
Probe several points in a grid.
You specify the rectangle and the density of sample points.
The result is a mesh, best for large or uneven beds.

Note that bilinear leveling is automatic leveling option that doesn’t require you to adjust any leveling knobs (but remember that automatic leveling is not magic, you still need to provide a bed as level as possible! see Does auto leveling result in sheared prints?), but it is laborious to use in the sense you typically have to run the multi probing points prior to printing, which can take some time depending on the grid size (see How to increase the amount of probing points for a BLTouch sensor in Marlin firmware?).
This is where Unified Bed Leveling comes in.
UBL
Unified bed leveling (UBL) introduces a mesh-based software procedure in Marlin firmware similar to (ABL) bilinear leveling but with some extra features. From the configuration.h file:

AUTO_BED_LEVELING_UBL (Unified Bed Leveling)
A comprehensive bed leveling system combining the features and benefits
of other systems. UBL also includes integrated Mesh Generation, Mesh
Validation and Mesh Editing systems.

A UBL mesh is generally using more probing points than the (ABL) bilinear leveling equivalent to create a better digital representation (topography) of the used build surface. Bilinear meshes typically use 9-25 probing points, UBL meshes generally use 81-100 probing points to scan the surface more thoroughly. Note that this is up to you how you define this, the bottom line is that UBL is not something you do prior to every print, so you can get away with having some more probing points. Note to choose a value that is in line with the surface (type and size), for a flat glass surface 100 probing points might not be necessary.
Essentially, the operator is presented a means to interact with the 3D printer to control the leveling to allows to easily store (save up to seven meshes), adjust, and swap multiple digitally stored leveling meshes on your printer to encounter the various print surfaces you may use like in multiple build plates.
The main difference between UBL and the ABL systems is that UBL combines features of other leveling techniques to provide users with more control. With Unified Bed Leveling, you’re not technically required to have an automatic bed leveling sensor. Through the interface, you can manually create the mesh! As the machine is homed, the coordinate system is fixed, movement relative to the reference is used by each probing point.
With so many points, creating UBL meshes can take a long time compared to other systems (certainly without a leveling sensor), but once the process is done, you don’t have to redo this again as the UBL features allow you to modify the probing points.
The G26 command is designed to use with mesh enabled leveling procedures (Marlin < 1.1.6 AUTO_BED_LEVELING_UBL and since Marlin 1.1.7 it also works with MESH_BED_LEVELING and AUTO_BED_LEVELING_BILINEAR). The various options are described in the Marlin implementation of G26.

Are they the same?

To sum up, ABL and UBL are the same in that some sort of procedure is used to scan the topography of the bed surface but they differ in the sense that for ABL you are required to have a automatic leveling sensor and choose less points while you can have more probe points using UBL including advanced features as editing and storing multiple meshes.


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What is homing? What is the purpose of homing?
A 3D printer needs to be homed (homing) before the print starts.

What is homing?
What is the purpose of homing?
Is it necessary?

What is homing?

From the tag wiki homing we can read:

The process of determining the location of a 3D printer nozzle in
three dimension using a reference point (home location) is referred to
as "homing". Homing should occur before every print and involves
bringing the X, Y and Z-Axis motors to pre-defined limit locations
(usually these are endstops). Pre-recorded homing data offset values
determine the position of the build plate origin with respect to the
endstop locations.

What is the purpose of homing?

So, homing is defining the printer coordinate system location with respect to a reference location we call "home". Why? The controller board or steppers have no memory for storing their position and could have been manually moved. Once the axes have "seen" there reference location, the printer will remember to refer all movements in respect to this point (this may include offset values to get to the origin of the printer (see How to center my prints on the build platform? (Re-calibrate homing offset)). Note, if a problem occurs where e.g. the nozzle hits the bed or print object, the nozzle may be out of sync with the reference point. Such an anomaly is e.g. layer shifting which occurs on open-loop stepper movement (servo steppers have feedback to prevent this from happening, but these are more expensive). The purpose of homing is to set a reference so that your sliced objects can be printed at the correct location within the printer print volume. If correctly configured, and no problems like layer shifting occur, the benefit is that proper homing prevent the machine to print within the limits of the printer.

Is it necessary?

Strictly speaking, no, it is not necessary. But if you do not automatically set a reference for each axis, you would need to manually provide a position to start from. This can work just as well, but the use of end stops automate the procedure so that it is very easy for the printer operator. Some (of the cheaper) CNC machines do not have end stops, the operator needs to be aware to position the tool head of the CNC machine at the proper starting position.

Most 3d printers control head position using stepper motors and end stops with no position feedback.  The stepper motor does not actually know its location.
The printer's control system can only know the location of the head by keeping track of the relative number of steps the head has been moved by the stepper motors.
Homing moves all the axes in one direction until it hits the end stops for each axis.  Once that has been done, then the control system knows exactly where the head is and future relative motions can be offset from there.
Some control systems will move the axis at a relatively high speed (so you don't get bored, but not fast enough to cause damage) and then overshoot the end stop's activation point and stop.  Then they will back off to release the end stop and then move towards it more slowly to get a more exact reading of the activation point.
When the printer is idle, frequently the stepper motors are unpowered to save energy and keep the motors cool.  When the motors are unpowered, they can free spin (you can push the axis with your hand or the vertical axis might even slip a bit with gravity), so the position would be uncertain, and it would be necessary to re-home.   Once it has rehomed, the control system will keep the motors powered to prevent slipping.
It is only necessary to home if you care about where the printer starts printing.  In theory, you could get away with only homing the vertical axis (so the print starts on a surface and the first layer is the correct thickness), and manually set the horizontal start position.  However, this might make using the full horizontal limits of the build area difficult if you didn't start it in the right place.

You mentioned that sometimes they overshoot and then back off to reach the "activation point."  Is the activation point actually repeatable enough to place things within a fraction of a millimeter (I'm thinking in the z direction), or do they need to rely on some other hard-stop to correctly pin down where the first layer should be painted?  it seems like an astonishingly accurate switch in my mind.

It's repeatable if you go slowly enough.

I suppose it would be more accurate to say the precision of the repeatability is inversely proportional to the speed.