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Alternative raft generation
For some recent prints I have been using rafts as generated by Cura to aid in bed adhesion; which helps, but is not as reliable as I'd like it to.
However, it seems to me that the raft generation could be so much better; if I explain what I have in mind, maybe you can explain to me why it is a silly idea; or save me from reinventing the wheel, if some other slicer already implements similar functionality.
What seems silly to me about Cura rafts is that the bottom-most adhesive layer consists of continuous straight lines. This is literally the worst geometry, in terms of being able to relieve its internal cooling strains. Peeling always starts at the extremities of those long first lines, where the accumulated strain overcomes the adhesion, as you would expect.
What seems to me much more optimal is to have many non-connected small 'suction cups' as a first layer; little circles or maybe literal point-like dots. And cover a solid percentage of the surface with those unconnected cups. Like a fine honeycomb pattern. And then use subsequent layers to connect these cups with wavy lines of decreasing spacing, to build a somewhat continuous platform, while still providing a form of natural strain relief within those lines. If you take enough layers with a sufficiently compliant structure, you should be able to master arbitrary spans, with arbitrary shrinkage.
Has this been tried already? Am I missing something? Or should I start writing my own G-code generator and figure out why it might be a silly idea myself? Speaking of which; are there any python libraries to aid in generating G-code from a somewhat higher level format?1

1 Forget about that last question; gcody seems to fit my criteria for not reinventing too many wheels.

Welcome to 3D Printing! What else have you done to ensure proper bed adhesion? What preps are you doing? How do you level your bed? What kind of filament are you using (PLA, ABS, etc)? What temps are you using on your bed and nozzle? The only time I use any type of brim is if the base of the print is too small to have good adhesion. I use a skirt quite often to prime the nozzle. I've never used a raft. I'm sure there must be reasons to, but I've never needed one ... which brings me back to ... what's happening that you need a raft in the first place?

Thanks for the input, but I am not looking to fix a particular print here, but rather to discuss rafts more in general. Will fix my introduction to reflect that; it might give the wrong impression.

As you should know as an experienced SE user, this is not the place for discussions. Please join us in [chat] for discussions.

Poor choice of words perhaps; there are a few delineated questions on my post that potentially have very clearly defined answers.

Before reinventing the wheel, you should fix your question to not contain all these rhetoric questions. Because some of these can't be answered by us, others are just tangentally to the seemingly actual question. To me this reads like "I have an idea of using a circle pattern for bed adhesion, then some layers of gyroid infill to provide a raft. Would this have benefits?" and then you asket the 2nd last paragraph

I second @Pᴀᴜʟsᴛᴇʀ2's question about material. For PLA at least, rafts are generally considered antiquated. You should not have adhesion/warping problems with PLA unless something is wrong with your setup, and rafts waste a lot of time and material and are generally bad for bottom surface quality.

@Trish yeah you summarized it well. Seems I am more effective in learning about rafts by generating gcode than by figuring out how to write an iso-compliant stackexchange post though, so I think I'll focus on the former.

If you have trouble in getting straight lines to stick, you don't have raft problems, you have bed adhesion problems :) Maybe focus on that first as the Cura rafts work perfectly for me and others (but I usually try to avoid them!). Those straight first layer lines are extra wide lines, these "should" stick relatively easily. I've even got rafts to work with POM, which is not easy to stick to the build plate. Please note that many people have problems is printing concentric circles (non sticking circular perimeters are posted here multiple times), they detach quite easily.

@R..Rafts for PLA are only needed in some few fringe cases: if the print bed is not uniform smooth but perforated. There was a printer in the early days that had such a setup, it could not be used without raft. Slim geometries also demand extra adhesion on unheated beds, and that can sometimes better be achieved with a raft than a brim.

Perhaps this question should be changed to just ask why it is common for a raft to have the bottom layer consist of parallel lines. Does this offer any advantages/disadvantages over other patterns.

@oscar; the question is, do the circles not stick because they are circles, or because they are extended objects? My mechanics intuition says a large circle and long line of equal size will take a comparable shrinkage to adhesion ratio to come loose. The key is to avoid contiguous structures along which shrinkage strain can accumulate; if they are dots or tiny lines or circles matters little I think

NOW you are onto something: when is a circle and a line not equal if their area is equal? The secret lies in how extrusion is done and that the pattern of circles would consist of many separate paths which are interrupted with moves between each while a line pattern could be one continious extrusion, guaranteeing a good surface coverage.

True, youd want to cover a large percentage of the area; though tiny circles/hexes could in theory cover an arbitrary percentage, what I am currently leaning towards is to simply print straight lines with small skips of extrusion in them, as this structure nests well and prints fast.

Here's a non-answer: use better technology.  What would you do if you could skip the raft altogether? I installed a WhamBam Systems bed system. It uses PEX material on a flex-steel sheet, that sticks to a magnet applied to the AL print bed. I've only printed with PLA; it sticks really well to the PEX with nothing else needed. When the print is done, the flexsteel sheet it lifted off the magnet, you let it cool for a minute or so, then flex the sheet in the X and Y direction and the part pops right off. I really like it.


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CR-10 Ignoring Z-Stop Switch, Keeps Trying to Lower
I have a CR-10 with TH3D's most recent firmware on it and an EZABL (Plug & Print Auto Bed Leveling Kit) installed.  My problem is that when I select "Auto Home", the printer ignores the Z-stop switch and keeps trying to lower the extruder, grinding and shuddering until I have to power it off.  I can't seem to figure out what the problem is.

Hi Jack and welcome to 3DPrinting.SE! Please explain what you mean by "Z-stop" is that the original switch or the inductive sensor? Also post which changes you made to the firmware to enable the EZABL sensor. As the question is posted now, there is not much information to work with for others to give you an answer.

Did it work before you installed EZABL?  If this is a mechanical Z-stop, have you verified separately that the switch (and the connector on the driver board) is making electrical contact when closed?

You may want to upgrade to TH3D's latest firmware (2.16a released on 10/2/2019). There's a fix in there that might relate to your issue if my rewire answer below doesn't work for you.
https://www.th3dstudio.com/knowledgebase/th3d-unified-firmware-package/

I had this same issue with my CR-10s. My black and white wires were reversed where I plugged them in to the motherboard in place of the stock z stop wires. I had to take apart the connector and swap them, as they came backwards from the mfg. Once I did that it worked perfectly.
The image I'm attaching helped me solve my issue. It is not mine, after much searching I found kenneycp's reply on this comment thread
https://www.thingiverse.com/thing:2975949/comments

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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Anet A6 ERR MAXTEMP BED error
Out of the blue my A6 printer displays a ERR MAXTEMP BED error and shows about 100 degrees on the bed even when just powered on.
A quick thermistor check shows that it's working properly : about 80 kOhm at room temperature, similar to other units (didn't bother to really check the specs).
Swapping the bed thermistor for the head thermistor connector does not change the temperature readings : the one connected to the bed input gets 100 degrees, while the other one works as expected, proving that the connector and thermosensor are ok.
It has to be in the board. How do I fix it?

the question clearly established the error is the board: the sensors in the bed were fine and the board refused to acknowledge so. Firmware also was fine because it triggered the maxtemp that is expected in case of a broken connection

I'm posting the answer here hoping that will help anyone that encounters a similar issue. A post on another site indicated that these boards are known to be problematic.
After some digging, I came up with the schematics of this part of the mainboard :

I'm not an electronics genius, but clearly it's not the capacitor; so that leaves the pull-up resistor or the microcontroller.
Since the printer is already unusable, no harm in trying to replace the resistor, which is located just next to the connectors; for the bed it was the second from left, but if you encounter the same issue with another input, you may need to locate the proper one.
Make sure you have the proper tools and knowledge for removing and soldering SMD components; in my case it was a 4k7 resistor in 0805 footprint.
Bottomline : replacing a less-than-one-cent resistor saves a month of waiting for the delivery of a $25 board.

For note: The C43 is the capacitor belonging to the defunct R37 resistor that was replaced. Search for the labeling.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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How to use a BLTouch or equivalent touch probe to 3D scan objects with a 3D printer?
I thought about using a BLTouch probe to do 3D scans of objects.
The objects to be suitable require smooth gradients and enough space for the probe, without anything hitting the print head/hot end.
What tools do I need to control the printer and obtain such data? are there GCodes scripts for that?
I would need to define a grid size, spacing, retraction, maximum expected height increase between adjacent points.

Why am I thinking there's no way you're going to get the resolution out of a touch probe you'd need to actually scan an object? I mean, it's only used for one axis of the three, which is the z-axis.

If you define a mesh and you test each node, you can produce a map. Of course the issue is the lateral rigidity of the probe: the pin should not bend laterally when the surface is not parallel to the bed

I don't know the probe, but I have used a delta 3D printing machine (of my design) to scan a surface.  It takes some time.
Your resolution will be limited by the probe geometry of the touch probe tip.  You want a Z-probe function that reports the Z-value of the point, not that simply sets Z= when the probe "hits".  The RepRap firmware has this in the G30 command.
You will need to write a loop that probes all points of interest.  This is best done by writing a program (or script) that generates the G-code.  I have a PERL script that generates the calibration mesh for my Delta machine, and I can share that with you.
I edit the script for the area to be scanned.  This includes (in my case) the radius and the resolution.  I then run the script to produce G-code to do the probing.
I send the G-code to the printer with Repetier-Host.  Repetier-Host builds a log file of every character returned by the printer.  The G30 command returns in the log the Z value wher ethe probe hit.
After the G-code is fully executed, I run a PERL script on the log file to extract the Z height of each of the probed points.
What you do with that data is up to you.

I wasn't aware of G30. It does what I need, the rest of the procedure is as I had expected it.

the resolution could be improved by using a very thin needle mounted to the tip of the probe to get better accuracy by having less probe area. The system relies on a very accurate set of stepper motors and making sure that the print head and bed have best no play on his axis. The process should be run slow to make sure there is no shivering in the bed. To get more than one side of the surface, multiple probings are needed, best with known turns between them.


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Horizontal line z-axis not printing correctly
I have just started with the FlashForge Creator Pro using the FlashPrint slicer software. I have gotten some nice prints but I am having an issue with a certain print from this model of a knife.
See image below:

Everything prints fine up to where the blade starts. As you can see, there is horizontal portion of the blade that juts out and, as I predicted, when it tries to print this, there is nothing for it to adhere to so it hangs there and when the extruder moves, it just pulls the filament around with it and creates a mess.
The object file from Thingiverse is designed that way (with it standing upright) and there are pictures on the Thingiverse page of a successfully printed knife. As I am new to this, I am wracking my brain trying to figure out how to print this.
I tried to cut the design and print the handle and blade separately (laying the blade down flat on the print surface) but the blade isn't perfectly flat on the sides so it doesn't lay flat. I suppose I could also just cut the blade and lay it vertically on the print surface but it seems as though it was designed to print in full in one piece.
Any help or any pointers in the right direction would be greatly appreciated. Thanks!

While not your question, I'd consider laying the knife down with the spine of the knife on the bed. You'd do this with using support as well. The reason I'm suggesting this is for strength in the blade. Layering the knife up through the blade like you are is going to leave it very weak. Laying it out lengthwise will allow the filament to be laid long as well, which will give it a lot more strength. Just a thought.

You'll notice in the screen capture that there is an icon marked "supports." This is precisely the solution required. When selected, the software should construct a series of vertical pillars in the locations required to properly print the horizontal portion of the knife blade.
It's common for Thingiverse models to have a notation Supports (yes/no) to indicate that this feature should be activated. Depending on the capability of your printer, some angles may require supports that are not required on someone else's printer model. There may also be an adjustment for angle reference to cease supports or to require. My printer will handle up to a 50° from vertical without support. Beyond that, more filament is used, but the result is superior to printing without it, as you've discovered.
Note also that support is typically categorized as "from the bed only" or "everywhere." The former prevents support from being generated between vertically separated parts of the model, while the latter permits it. Some models may have, for example, a foot on the bed not requiring support, but the arm directly above the foot does. "From the bed only" means the arm would droop/fail as no support would be generated above that portion of the model.
If you are using the ReplicatorG 0400 software, referenced from the manufacturer's web site, page 11 of the manual will have additional information regarding support within the program.

Oh perfect, thank you! That screenshot is actually from FlashPrint (from my computer) which is the software the FlashForge Creator Pro recommends. When I went into the 'Supports' screen I was able to see how to set up supports in order to do that. Thank you, I will play around with this to get it right but it looks like that's the answer!


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G28 ignoring Z-Probe X/Y Offsets
I recently installed a SKR 1.3 Board with a 3DTouch-Probe on my Creality Ender 3 Pro.
The probe works, G29 does its magic, but:
If i issue a plain G28, the hotend first homes X and Y like before the Z-probe.
The probe is now next to, not above, the bed.
As the next step, the printer is supposed to home the Z-axis. The probe deploys and Z starts to lower until it smashes into the bed, because the probe misses the bed (if I don't stop it, that is).
I configured X/Y offsets for the probe, but they don't seem to be honored when performing the G28 code.
If I home X/Y "manually" with G28 X Y, move the hotend with like G1 X45 Y10, then home Z with G28 Z it works fine.
What did I miss? Is this intended behaviour & the user has to take care never to issue a plain G28?!

You need to enable the constant Z_SAFE_HOMING (like: #define Z_SAFE_HOMING) in your printer configuration file (if you're using Marlin firmware that is). This will move the nozzle to the middle of the plate prior to lowering the nozzle by default:
#if ENABLED(Z_SAFE_HOMING)
  #define Z_SAFE_HOMING_X_POINT ((X_BED_SIZE) / 2)    // X point for Z homing when homing all axes (G28).
  #define Z_SAFE_HOMING_Y_POINT ((Y_BED_SIZE) / 2)    // Y point for Z homing when homing all axes (G28).
#endif

Use Z Safe Homing to avoid homing with a Z probe outside the bed area
According to Marlin firmware with this feature enabled:

Allow Z homing only after X and Y homing AND stepper drivers still
enabled.
If stepper drivers time out, it will need X and Y homing again before Z homing.
Move the Z probe (or nozzle) to a defined XY point before Z Homing when homing all axes (G28).
Prevent Z homing when the Z probe is outside the bed area.

To Enable Z SAFE HOMING, In the configuration.h file search (Ctrl+F) for #define Z_SAFE_HOMING. By default, it will be disabled to enable it just uncomment
the line


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How to tell if a nozzle is truly stainless steel?
Normally stainless steel is magnetic. But whenever i order stainless steel nozzles from Amazon, they are not magnetic. This makes me think they could be brass coated in something like aluminum. However, there are many types of steel.
I've attached an image of someone who reviewed these nozzles. He says they are not stainless steel because they are not magnetic.

But whenever I order "stainless steel" nozzles, even from other sellers, they are not magnetic. i already returned one pack from another seller and just received a nonmagnetic one from a third seller.
So that's it? Amazon just sells junk now? Or is there a way I can easily tell whether these are something other than colored brass / good for abrasive or high temp printing. Here is the product that was reviewed:
AUSTOR 13 Pieces Stainless Steel 3D Printer Nozzles 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm Extruder Nozzle Print Head for E3D Makerbot https://www.amazon.com/dp/B07CHZMGRH/ref=cm_sw_r_cp_apa_i_XtrNDbRMVH8SW

Stainless steel (at least the versions I've tried) are not magnetic, so I'm pretty sure that's not a way to tell.

But a screw (like the reviewer includes in the photo) is stainless steel and is very magnetic. Still, your comment helps.... Does the nonmagnetic kind hold up better than brass?

That's not stainless ... it looks to be zinc plated. Stainless isn't shiny like that ... unless it's in silverware.

This bolt is stainless ... this bolt is zinc coated.

There's always the Archimedes test. Submerge an equivalent mass of known-real steel in a clear glass of water and note the displacement. Then submerge your hot end. If the displacements are similar, they are the same material. But for what it's worth, Amazon has always sold junk.

@steveantwan Some stainless steel are magnetic, this depends on his grade. the main test is simple; just add water then keep it one or couple of day out side, then see results.

The correct answer is the one about Archimede. It won't distinguish between steel and stainless steel, but it's a good step.

Let's preface, that there are a LOT of metal identification methods. For example, I found this guide helpful and I had been at the scrapyard lately, where I have been told that 90+% of the time, steel objects that are non-magnetic are the more valuable stainless steel. The kitchen sink I dropped off? Stainless, non-magnetic steel. That's because about 70% of the made stainless steel is Austenitic Steel, which happens to be generally non-ferromagnetic.
Magnetic test
A common test in scrapyards is, to check if an item is magnetic, as a lot of stainless steels are non-magnetic and then prove to be iron metals with a short spark test (see below).
Tempering/Annealing behavior
The very fact that the nozzles do change color to a brassy color that is commonly called straw is proof that it is indeed steel: heating up a piece of steel does alter the steel and also alters the surface color in a process called tempering. The color is only the surface, and the mild straw color would become orange-brown, purple, pale blue teal and yellow if you were to heat it higher. Take a look at the tempering colors of steel here:

In contrast, brass acts differently when heated and tempering is somewhat different. Subjecting the piece of brass to heat you will not temper but anneal it and you get colors differently. Instead of becoming straw before blue, Brass becomes dark, starting with its pale gold to go over a dark "antique" look to before going green, teal, purple-blue, red and then losing its color like this piece of a polished brass plate shows:

Hardness/Chip
Another test that would be easy to conduct is hardness. The base idea of hardness is: An item can scratch a piece of equal or lower hardness, but not of higher hardness. If you have a chisel handy, then you have a piece of steel at hand. Most chisels are rated as HRC 58-62 - which is the Rockwell hardness scale. Brass could be all over the place, depending on work hardening. But the identification is not by the hardness but by how the chisel - or better a graver - cuts.
We expect Brass to get a smooth cut with saw tooth edges while stainless cuts smoothly and has sharp edges to the cut.
Sparktest
If you want to scrap one, get an angle grinder or another power tool to grind at the nozzle. Steel sparks red-orange to whitish and depend on the mix, Carbide sparks very short and orange. Stainless creates a HUGE shower of sparks, yellow-white and dense, no burstes and branching. Copper, aluminium and Brass do not spark. Titanium is very bright white. It can tell you what kind of steel you have: Stainless steel typically has medium-to-long, non- to low-branching, non- or low-exploding sparks.

Drilltest
As we are at destroying a pair of nozzles, why not drill them? we should have done that before subjecting it to heat treating and grinding, but alas... Basically, we clamp the piece down and take an HSS drill to drill out the center.
Brass needs a different drill type but can be drilled and machined without coolant. Typical HSS drills from the home depot have a positive rake, brass wants a neutral or negative rake to drill or machine smoothly. If the piece grabs, creates short spials and dusty small flakes with an unmodified, new drill (or under positive rake machining), it drills like brass, as you see here from a Clickspring video on drilling brass:

In contrast, stainless steel doesn't want to be machined without cooling at all and using high speed creates smoke quickly and nearly no chips at all. A moment later your tool starts to glow and gets a dull edge. If your drilling experiment turns a new drill blunt on high speeds or uncooled, you have stainless at your hands. To get chips, you need to work slow and have some sort of cooling. It is still a painfully slow process that needs a lot of pressure, but it gets larger, nesting chips like seen here from a Wayne Canning steel drilling tutorial:

Rust test
If you have established it is an iron metal via spark testing, you also have an exposed surface. There are commonly three tests to see the quality of stainless steel, which will show only minimal rusting on such an exposed surface.

Copper Sulfate Solution will react with most non-stainless steels or contaminated stainless steels quite aggressively, while stainless steels react only minimally.
A high-humidity warmed chamber at about 30 °C results in a dense rust layer within 24 hours on exposed steel. Just dumping into water will do so too, so into a bucket and wait a day. If it's all over rusted, it's not stainless.
Saltwater spray is very corrosive on non-stainless steels, resulting in accelerated rust. While this test typically is run as a stress test for days or weeks to test exposure to marine life, a few hours will rule out non-stainless steel.

A Q&A answerer from the Amazon page that the OP linked to says that they have machined the nozzles and reckons that they are stainless steel, which goes along with the suggestions in your answer to try machining it and see what it's like.

Good answer, but what about steel vs stainless teel?

see the new spark-test picture @FarO

Stainless steel is created by adding elements (usually Chromium, but also Nickel) to steel. These added elements form an oxide layer with the outside air protecting the steel from corroding.
Whether stainless steel is magnetic or not depends on the added elements and the micro structure of the steel; some are and some aren't magnetic.
From physlink:

As for whether they (red. stainless steels) are magnetic, the answer is that it depends. There are several families of stainless steels with different physical properties. A basic stainless steel has a 'ferritic' structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them 'martensitic') and are often used in cutlery. However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

So the answer is that you cannot determine by testing for magnetic properties if the nozzle is stainless steel or not. But if it is not magnetic, it can be stainless steel. Note that discoloration is possible, this is the oxide layer.
To identify if the steel is stainless, you could without sacrificing the nozzle (according to this reference):

Step 1
  Stick the magnet on the piece you are testing. If it holds firmly, the metal is possibly stainless steel. If not, it is (red. could be) another metal such as aluminum.
Step 2
  Pick a spot on the piece that you don't mind damaging a little.
Step 3
  Fill the eye dropper with muriatic acid. Drop a small amount of the acid on the test spot. Wait half an hour.
Step 4
  Wipe the acid off the piece. Examine the test spot. If it is discolored, the piece is stainless steel.

Note that the image you posted shows a Zinc plated steel screw, not a stainless steel screw.

It seems to me that Step 1 reveals nothing according to previous quote "...that depends," which makes me doubt the muriatic acid (hydrochloric acid) test is valid, especially as it says nothing about the nature of the discolouration (I could be wrong). A better test might be to file a groove in the surface and immerse it in salty water overnight: if it goes rusty, it isn't stainless steel.

@AndrewMorton I've left it as a quote of the complete steps, but indeed step 1 is not necessary considering the other quote. If I would have left out step one, I would have received comments about "where is step 1". Thanks for the comment, if you have a better reference, please feel free to alter the answer.

Anecdotal note - In the late 1960s the USN machine shops I served in used a nitric acid test with instant results. Carbon steel stained black; monel (a salt-water resistant copper nickel alloy we used extensively) stained green; stainless steel didn't react at all.

The other answers are good. For a more practical answer:
Magnet test
As answered by Trish, steel with an austenitic atom structure, which most stainless steels have, are not magnetic. So forget the magnets. Metallurgy is complicated.

Density test
Brass has a density of 8.5 - 9, stainless steel is below 8. Depends on the alloy. Might be a bit tricky to detect such small differences.
Hardness test
Better to do a hardness test. Hammer a nail made of mild steel into the nozzle, if the nozzle is softer than the nail, it's brass. If it's harder, it's stainless steel.
There are also HRC hardness scratch tests for that, although more intended for testing hardened steel. Find a chunk of structural steel and scratch the nozzle into it. Stainless steel will scratch the structural steel, brass & aluminium will scratch itself.
Spark test
Use an angle grinder or a dremel tool: if there are sparks, it's steel. This is probably the easiest method.


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Making Polyurethane molds with PLA (or ABS) 3D printed master
I want to make Polyurethane molds for concrete using 3D printed PLA or ABS master object. like this video:

 (this video is not about concrete of course!)
I'm not sure if it will stick to PLA or ABS master or not! if it does stick, whick wax material can solve this problem... Do I need to print my masters with another filament?

The process is the same for concrete molds just need a sealer then an agent release. https://www.youtube.com/watch?v=LZbikO7HUrE here is a video for concrete process.

I'm concerned about the interaction between Polyurethane and PLA!

Check the curing temperature of Polyurethane if the temperature is lower than the softeting PLA temperature won't be problems. softening temperature is between 10 and 15 lower than melting temperature. However I´ve seen other creaing molds from PLA, just google a little more to dissolve your concerns.

I was told that this type of polyurethane for making molds, needs a hardener and no melting is involved in the process.

@FernandoBaltazar PLA starts to soften and deform as low as 60 °C

@2012User I said check temperature values to avoid melting or deformation during process; I sent a link to review that process with agent release and also a smootherner surface soluble lacquer to avoid damages the original part. But if the curing process of polyurethane is higher that melting point will be problems.

@Trish Thanks Trish, so this will make mess for big parts.

@FernandoBaltazar Big parts? I would print in parts and use ABS and use ABS-Acetone to fuse the parts together.

In my experience, polyurethane sticks to PLA like super glue, not good. But silicone and alginate doesn't stick at all.
What I do is print the model of the mold with PLA or ABS, no matter. Then, cast a mold of the PLA model of the mold with alginate, then you have the negative of your mold.
Now with this alginate mold of the mold cast your actual mold with silicone. And then you can cast your part on polyurethane in the silicone mold.

Temperature
As polyurethane cures (or hardens), it undergoes a chemical bonding reaction, linking the mono- and oligomer strings in the components into long polyurethane chains. The chemical reaction is exothermic, it creates heat.
So, we have a process that heats up the polyurethane mixture as it hardens, but how much? Well, it's hard to find numbers for it, but I suspect it can easily reach 30 to 40 °C, depending on the mixture (fast curing) it could easily go higher. To combat the effects of heat softening of the PLA/ABS model inside the mold, I strongly suggest printing with extra shells and extra infill. While most items can get away with 10 %, in this case, I suggest 20-30 %. ABS would be the superior choice above PLA as it starts to deform at a higher temperature. PLA can start to deform at around 60 °C, ABS only at about 80 °C.
The temperature of the PU curing depends on the speed of the curing process - it is safer for the masters to choose a slower curing mix as the heat is generated over a longer time and the maximum temperature is thus lower as a result (as excess heat is lost to the room)
Surface
To reduce the sticking to the surface from the material creeping into the gaps of the model, it has to be as smooth as possible and best also sealed. If you choose ABS, a quick acetone vapor bath would do the trick in this case. PLA should be lacquer sealed as it doesn't like to stick to most waxes.
Adding a mold release agent isn't necessarily needed, but could help in removing the masters from the mold.
Conclusion
ABS might be the better choice in this application. It is advisable to use extra-thick walls (3+), a lot of infill (20-30 %) and a vapor smoothed surface.


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Anet A8 Clone LCD not working after flash
My Alfawise EX8 (Anet A8 Clone) had an issue, so I flashed the firmware provided on the GearBest page. After the flash the LCD is no longer doing anything and I can't really identify the LCD to confirm whether the correct one is selected in configuration.h
Currently the firmware had 'Mini VIKI' selected, but I'm not confident it works.
I cannot see anything on the screen, but I can still turn the dial and click things to make it do stuff.

I really hope somebody can help!

Why do you rephrase and repost the question, please use a single account, you can always edit the question.

Hi Ollie, would you like to have this account merged with your other account which you used to post the nearly identical question? How do these two questions differ?

Download a clean copy of the firmware from the official site (https://github.com/MarlinFirmware/Marlin/tree/bugfix-2.0.x) and adapt the changes from the firmware you've downloaded.
That display appears to be a standard-ish "RepRapDiscount Full Graphics Smart Controller", but certainly not a "MiniVIKI"

Probable duplicate of Alfawise EX8 Flashing issue

@towe That will not work as the printer uses a specific Melzi board that is not available in Marlin, only in the vendor's link to a fork of the software. It uses the standard Melzi pin layout at first but then redefines pins, notably LCD pins.

@0scar One of the "Sanguinololu" types, like Tronxy uses? That's rather easily added in; https://github.com/Lauszus/Sanguino
Do you have a link to that manufacturer firmware?

@towe Yes it is a "Sanguinololu" type, link to firmware is found here, I updated the question with the link.

According to the link to the fork of Marlin you need to be sure that a bootloader is present before flashing, see pins_MELZI_WYH.h:

/**
 * Melzi (WYH) pin assignments
 *
 * The WYH-128 board needs a bootloader installed before Marlin can be uploaded.
 * If you don't have a chip programmer you can use a spare Arduino plus a few
 * electronic components to write the bootloader.
 *
 * See http://www.instructables.com/id/Burn-Arduino-Bootloader-with-Arduino-MEGA/
 */

From this same pins layout file you can find hints to the usage of the REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER display:

// For the stock M18 use the REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER
//   option for the display in Configuration.h

Maybe you can use that one instead of the "Mini VIKI". Though, an internet search, does hint to the "Mini VIKI" being the correct display for this printer, but it does look different from other Mini VIKI displays.
Note that in the Configuration.h, by default this display is not enabled as can be seen:

// RepRapDiscount FULL GRAPHIC Smart Controller
// http://reprap.org/wiki/RepRapDiscount_Full_Graphic_Smart_Controller
//
//#define REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER

I know this is a closed and already answered question, but for anybody having an Alfawise EX8 and wanting to update the firmware, I've changed some things in the Marlin bugfix-1.1.x version, so that it now works perfectly with this printer. You can find it here. The issue with the display is in the file ultralcd_st7565_u8glib_VIKI.h. The Alfawise EX8 version contains added functions like contrast adjustments and addressing offset, which is not present in the Marlin vanilla version. Also, the original Alfawise firmware grabbed 93% of RAM for global variables, which lead to unstability and in my case to spliting screen and other issues. Now there are only 46% allocated. I suspect the SD alpha sorting of this, as you can clearly see in the advanced config, that it creates an array of more than 200 instances. 37B each. Sooo since I don't usually hoard gcode files on my SD card, I disabled the sorting completelly. Feel free to make adjustments to your own taste!
Wish you luck and many successful prints! :)
EDIT: If you are still experiencing glithes with the LCD, try separating the LCD data cable from the extruder cables. I didn't. My bad. Also, don't add capacitors between power inputs. Caused more problems than it solved and yes, I know how to connect an electrolytic capacitor. The firmware is fully functional, working with a MightyCore bootloader inside. There was an issue with the SD print abort function. In the bugfix version, there is a gcode function added to abort SD print and it somehow doesn't work too well with the LCD option. So I removed the gcode from Marlin_main.cpp and brought some things from the original firmware to get it working. Also since the SD was really slow, I had to re-enable the alpha sorting using RAM, but decreased the array size to 30 instances. For the memory it means, that right now it is at 89% Flash and 39% RAM usage. Enjoy! :)
BTW: For anyone saying that you cannot print good prints on this printer, I just printed tha Maker's Muse Gauge and clearance test model, and got it moving completely! That's pretty awesome for a printer that cost me less than 150€.

This could be very helpful to others! Even better would be to incorporate this into creating a pull request to save your code changes to the original sources and rewrite your answer to point to the code changes!

Thanks. Sadly, the LCD is still glitchy at times, so I'm trying to figure out the problem right now. Just thought to put it down for now to avoid unnecessary issues.

Sorry, I wasn't aware that it was glitching. Please mention that in the answer as well as your code changes. If you work it out please update the answer! Hope you get the glitches out!

In fact it seems like a bootloader issue. Now it crossed my mind that when I bought the printer, it had no bootloader and when I tried optiboot, the display would not work. It works sort of with the sanguino bootloader, but I'm gonna try to just flash the firmware via ICSP. I will update the post as I manage to get it working properly.

I have the same problem.
I think it is not a bootloader problem because the screen is all blue but machine can work with serial connexion. I tried to use the new Jakub's file but it doesn't work either.
I found new type of screen for EX8 on Marlin V2 called "WYH_L12864_LCD" - Has anyone tried this solution?

Hi and welcome. Could you [edit] you answer so that it isn't another question? Otherwise it could end up being deleted as "Not an answer". Either that, or ask another new question (you can refer back to this question, using the URL, if need be). Please take the [tour] to get a better understanding of how the Q&A mechanism of Stack Exchange works.

Please try the "WYH_L12864_LCD" solution yourself and see if it works, you can then change your answer in a proper answer, even if it doesn't work. Otherwise we need to move this answer to a comment on the Question or delete the answer. "Me too" answers are not allowed. Please remember that SE is a Q and A website, not a threaded message forum.

Sorry. I thought publish a new question with the same content was not good idea. I would like like to publish as comment but website blocked me (missing 50 reputation). I'm going to change this publish soon.


text:
How to extract 3D information from a 3D model for calibration?
I made two "OBJ" 3D models of myself using Sense 2 scanner and using photogrammetry with Meshroom.
I would like to extract some information about myself to be able to scale the model properly and to be able to compare the accuracy. For example, distance between shoulders or circumference of the neck/chest. Another option would be to hold a reference parallelepiped and then scale the model based on the known distance between faces.
How can I do that? I can calculate the distance between points I can click using Meshmixer, but circumference or the distance between parallel faces is more difficult. The tools Meshmixer offers for the purpose don't seem to work well.
What are my options?

Faces are unlikely to be parallel if they come from photogrammetry, and the circumference of a polygon is always a bit tricky.
In lieu of a known prismatic object to measure the dimensions of, perhaps the distance between your eyes could be used.

Extracting various measurements from 3D models is easily done using the following free online tool:
https://0x00019913.github.io/meshy/
I scanned a person using the Sense 2 scanner and I compared the values from meshy for the hip and waist with those measured in real life one day after the scan: the difference was about 1 cm, which can easily be explained by the uncertainties in the choice of the measurement point and moment of the day.
This shows that both the 3D scanner and meshy are quite accurate. The tool is also very easy to use.


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3D printing overhangs that are over .200 in
I am new to 3D printing but have been in CNC Machining for a few years. I have a part I am trying to print that is a cylinder 1.000 in. in diameter and has a .200 in overhang starting at 1.300 in. In other words I am printing a 1.300 in. cylinder that is 1.500 in. tall that at 1.300 in. its diameter increases by .200 in.
When I first printed the part the overhang had sunk or fallen out. Not by much and is still usable but made a crappy finish. What would I need to do in order to have the overhang not drop as the base layer extended outward .200 in. at 1.300 in.?
I tried slowing the feed rate but that was worse. I also lowered the temp to 195 °C.
I am using a Monoprice Select Mini running at 200 °C and a 1.0 Speed (Not really sure what that feed rate is in terms of mm/s). Based on what I've seen so far I would increase the speed and keep the temp at 200 °C.

Any suggestions, I hope I have explained my problem well enough.

Less printing temperature may help, but in the end, you're still trying to print in thin air.
Consider if it's possible to flip the cylinder, or use support structures.

Hi and welcome to 3DPrinting.SE! I guess you mean 200 °C not Fahrenheit (200 °F is about 93 °C). Furthermore, a picture says more than a thousand words. :)

Can you print the part upside down, so you have a ledge instead of an overhang? Also, what are your slicer settings for support material?

Thx for the replies. I've edited the post and added a pic of the part. @towe I did experiment with different temps and it seemed to work better at higher temps. I am not sure how to use that support setting. I looked into it and once checked boxed it has 2 choices, Everywhere and Buildplate. Not sure what everywhere would mean or look like.

I can print the part upside down and it works fine, but the top surface is then mared after removing the raft. It would need additional finishing, which I may just do if I can't get it to print right side up.

@apesa: Raft? Generally rafts are considered antiquated. If you can't print without them you should try to figure out what the underlying problem behind that is

@R.. safe for perforated print beds. Some old machines have them and you deliberately use them in Polycarbonate printing to get extreme bed adhesion due to the extreme tendency to warp.

@Trish: Aside from materials with special adhesion/warping needs I'd just clip a buildtak surface onto the existing bed and avoid wasting all that time and material for a raft every time you print...

I suspect this kind of overhang (90° as opposed to more than 90°) could be printed without support if slicers were smarter - it would involve printing perimeters outward starting from the self-supported part, with some overlap in the nozzle positioning to improve bonding to the previously-laid-out perimeter. But as far as I'm aware, none of them support doing this.

Is the overhang itself a functional surface, or is it only needed because the top of the part needs to be a different diameter from the bottom? If the latter, you could simply design it so the diameter increases more gradually, so it forms a 45 degree slope instead of a 90 degree flat surface. That will generally be safe to print without support material.

The world of 3D Printers usually uses the metric system, especially in nozzle sizes. 0.2 inches are therefore better referred to as 5 mm, which is a considerable amount: that's 11 to 13 perimeters from a 0.4 mm nozzle, depending on extrusion width (0.46 and 0.4 mm respectively). Furthermore, the bore of the item isn't supported either, it is bridging.
To print overhangs and bridging without sagging, one should activate the generation of support material in the slicer.
Generally speaking, PLA (judging from the print temperature) doesn't need to be printed with a raft and would be better served with a brim for bed adhesion, unless you have a perforated bed. If you have to print in the shown orientation, then you should activate support generation in your slicer.
For this part, however, there is a better solution: it is of very simple geometry and it doesn't have to be printed as shown but equally could be printed "upside-down" by being rotated around the X-Axis by 180° in the slicer. This has two benefits: it removes all unsupported overhangs an avoids support structure, making the wasted material pretty much nonexistent.
I strongly recommend taking a look at my 3D Design Primer and the excellent question on How to decide print orientation? and then delve into further reading:

How to print an overhanging arc
How can I improve the overhang angles my printer can successfully print?
Is there any setting that could allow me to print this overhang without support?

Thanks much. The .200 refers to the part and not the nozzle size. I do all my CAD in inches. As for the raft, I am using that method simply because i'm still learning the intricacies of print setup and I much appreciate your links above. I am sure they will shed a lot of light on how to go from CAD to printer.The other challenge for me is to not think in terms of CNC milling and in terms of printing and optimizing the design for the printer and not CNC. Question, is there a preferred Slicer?

@apesa As far as popularity, Slic3r and Ultimaker Cura (and progras using the cura engine) are among the popular free one, Simplify3D is very popular on the paid ones.

It appears that your part could be printable upside down. If possible, I'd highly recommend this, as it mostly avoids supports all together.

Thanks, I printed it upside down initially and found that it created a rough top surface area bc I was using a raft for bed adhesion. I am looking at using a Brim and flipping the part back upside down.


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Anycubic Kossel Plus raises the Printhead around the corners of the bed too High if the print is too close to the corners
Hi guys I am quite new to 3D printing. I am having this problem with the printhead rising too high during printing when it gets near to the beds' borders. It isn't a problem with smaller prints but it gets very frustrating with bigger ones. I am thinking I am doing something wrong with the calibration but don't know exactly what. I am not calibrating by hand rather using auto calibrate.

I am using Cura 15.04.03 as slicer.

That doesn't look like the printhead lifting but warping...

I could put a video of it doing it. On the the picture i also got the excess material off so maybe thats why it looks like warping.

wait, you use cura (1.)15.04.03? You should seriously update to cura 4.X!

It is a common  problem with "delta"-style circular parallel kinematics machines.  It is called Bowling.  It can lead to the presumed Z=0 plane having a bowl-like shape.  The actual error shape can be more complex.  The job of "bed-leveling" is to make the realized z=0 plane to be identical with the bed.
If you can, use a multi-point (like 40+ points) interpolation.  It builds an error map, and adjusts every point based on that map.


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Is it possible with current 3D printers to print a sound trace?
Is it possible with the accuracy of current 3D printers to print a sound trace?
On a vinyl record the grooves in the record are an encoded sound. Is something like this doable with 3D printers?
If Vinyl-like isn't possible, could a sound be printed at desktop scale? I mean printing the waves out that if you ran your finger along it it would reproduce the encoded sound? Examples would be Rumble Strips, the Musical Roads or highway rumble strips.

The practicality and the quality would depend on the size of the needle (and the RPM) that is used to play the sound back. I would guess that it is possible but the sound quality would be so poor that it wouldn't be worth it, except for academic purposes. Or are you asking if it is possible to print to a resolution comparable to that of a conventional gramophone record? If the latter, then I would guess not (yet). You'd need to compare the physical resolution (in microns) of record grooves to the smallest movement possible on a 3D printer. IDK but I'd guess they are at least a magnitude apart.

Just a comment, since I feel like adding this as my own answer would plagiarize what's already here, but I also want to sum up the two answers so far, since each covers a different aspect of the question. In short, we're getting close, but current technology can't do the equivalent of vinyl record playable on your parent's hi-fi phonograph machine. The grooves are too fine. But you could print a similar device, where the grooves are much wider, capable of reproducing intelligible human speech or even music, albeit at lower quality than vinyl.

@JoelCoehoorn No reason the fidelity can't be decent so long as you allow a faster speed (think 78 vs 33&1/3) and a larger vertical displacement.

Sound Encoding basics
Sound is a compression wave, and any depiction of it has to be an encoding of it. You can encode it so you can recreate the sound using a contraption that oscillates in the right way to compress air again in the right pattern, but you can't just "print it out" like you can scale up a lightwave from the nanometer scale to a visible one as a representation.
Let's take a simple example: a 440 Hz tune is generally considered to be the A4, aka concert pitch a or A440.
It could be encoded in a various ways. The probably oldest is to encode it as a note in violin notation, which then could be reproduced by anyone using a properly tuned instrument. The actual result depends on the instrument used as much as on the skill of the player. Each instrument thus might decode this encoded note differently, based on the physical setup of the instrument. Each instrument automatically creates the appropriate overtones.

In Midi, it is encoded as Note 69 and any machine that can decode a midi file could use this instruction, paired with an instrument to use, to create the A4 that is set for it. In Midi, the mere instruction of Note 69 does cut out skill, but how it sounds and feels comes from the instrument setup - which contains information about what overtones are to be created when playing this note.
For a physicist, the pure sound is encoded as just the notion of 440 Hz and some amplitude to balance how loud it is. With those instructions, he'd be able to set up a device that has these creates a 440 Hz tune. To generate the sound and feel of an instrument, the encoding for a physicist would need to contain all the overtones that are to swing with this one sound.

History of sound recording
Let's look at the very first way of recording sound: The Phonautograph of 1857 used a piece of paper or a sheet of glass blackened and then a membrane move a needle. When the plate would be moved, the needle left a written path. The encoding was done via 2 factors: the setup of the stylus (mainly how long is the arm) and the speed of the movement of the plate. Changing either changed the encoding. A longer arm would record a larger amplitude (making fainter sounds recordable) while faster movement would alter the timescale recorded, allowing to look at short instances and better compare them.
These vibration-pattern records could be used to measure and compare sounds but not be used to recreate the sound, as lines on paper nor scratches in soot are a good way to keep a reading needle in boundaries. it took till 2000 and the use of scanners as well as digital processing to recreate these recorded sounds.
The solution to recreate sounds was found by the Edison Laps in 1877 with the phonograph, which used a piece of thick tinfoil to record the motion pattern of the membrane. Again, then encoding was done via the arm setup and the speed at which the tinfoil clad cylinder moved (or rather rotated). It would till the 1880s develop to a wax cylinder, which was easier to inscribe and reproduce from. One such machine was used by Carl Orff.
The first Gramophone came in 1889, mainly altering the shape of the recording medium from cylinders to the well-known shape of vinyl records but made from hard plastics and shellac. Around 1901, a 12-inch gramophone disk held only a 4 minutes track, speaking volumes about the problems of encoding the complex patterns of sound onto a disk. At the same time, an Edison Amberol Cylinder held 4 minutes 30 seconds but would spin at 160 rpm. Soon after, celluloid would become the recording medium of its time, and the disk the de-facto "standard" as it was much better storable.
In 1925 finally, a real standard was developed to record at around $78^{+0.26}_{-0.08}$ rpm, which lead to only a 0.34 rpm difference between areas of 60 or 50 Hz mains voltage (though they needed different encoder rings), making records interchangeable between both machine types. All these recordings were encoded naturally: the vibrations of the membrane in the recording tool would be 1:1 transmitted to the vibrating stylus that would then do the encoding in such a way that a machine would reproduce what the recording one "heard" quite accurately.
When Vinyl came to the playing field as a recording medium at the end of world war II, so came a swap in the reading needle type: instead of a needle that would agitate a membrane directily, sapphire needles that would agitate an electrical pickup which in turn would activate a speaker. But while the recording technology advanced, the track length of a 12-inch disk was still limited to about 4 minutes at 78 rpm. It would only reach more than this in the last years of its use by applying LP technologies to pack the track tighter in the 1950s, achieving 17 minutes.
1948 came the LP, what we know as a classic vinyl record. At its introduction it could cram 23 minutes onto one side, making this possible by only using 33.5 rpm as the recording speed and thinner, much tighter coiled groves, increasing the information density by a factor of 5.75 for a 12-inch disk. 7-inch 45 rpm "singles" came out 4 years later. Within 10 years, the 33.5 and 45 rpm encoded variants had almost completely replaced the 78 rpm market.
Vinyl
As the history of analogous recordings shows, encoding a sound signal is rather easy in theory, hard in practice. A typical 12-inch LP Vinyl record of 20 minutes is a grove that is  427 meters long and coiled up 667 times. That means a single groove is between 0.04 and 0.08 mm wide - with an equally thin wall between. That means, that to achieve a printed phonograph record, you'd have to print accurately down to 40 microns to get an empty track. However, we also need to add the signal atop. And here comes the real problem:
An empty track has some 22 µm deviations, which the needle will usually not pick up at all. Dust, which creates the crackling at times, is in the same area (1-100 µm). The actual sound signal is encoded to have features as small as 75 nanometers. That is 3 magnitudes lower than the mere geometry of the grove, and equally much lower than any printer - including SLS - can achieve today, as 50 µm is often considered a lower limit in 2019.
To show how much tiny defects would ruin the sound quality, look at this rapid cast of a vinyl record. The resolution of the negative and the subsequently cast record is good enough to recognize the music, but the resin cast did contain so many gas bubbles that the noise level of the copy is very high.
Bonus: Unlike on cylinders the encoding of the signal on disks changes from the start to the end! The vinyl spins at a constant rate, but the radius from the center changes, leading in the speed on any part of the grove to be different as $|v|=|\omega \vec r \sin(\theta)|$, where omega is the speed in rad per second, theta is the angle of the reeding, so in this case, the sinus term becomes 1 and vanishes. This factor has to be taken into account for encoding so the pitch of the record doesn't change if the record is not created naturally by inscribing the signal onto a spinning disk.
Other encoding
Rumble Strips
However, it is quite easy to create a structure that creates sounds based on interaction with another body. Highway Sound Strips create sounds as the car tire bumps up and down, turning the car and tires into resonance bodies while the street "beats" upon it. In the case of a large percussion instrument like a car, we are talking centimeter scale.
Peg-Cylinder
A very simple method would be to go back to encoding and check out the note notation but limiting the length of notes to one unit. Encoding music this way results in pegs or ridges on a cylinder, which then can be used to actuate a mechanism to decode the music and create sounds like in a music box. In a music box of this kind, the demand for accuracy is about 3 to 5 magnitudes lower than in vinyl records: we speak about a tenth of a millimeter to centimeter scale.
Such a Musical box or noisemaker can be easily printed and is pretty much a rumble strip coiled around a cylinder. The length of the sample is determined by the resolution, playback speed and diameter of the cylinder while the complexity is determined by the rows of pegs of it: a noisemaker is pretty much a 1-note, high speed, music box. Typically, one rotation stores about 25 to 30 seconds. Typical examples would be the first part of Für Elise,  or the Marble Machine (Between second 30 and 35 the encoding wheel rotates 1 fifth). Some barrel organs also use the peg method, like one can see here. With some trickery, one cylinder could be used to encode multiple parts that play one after another once a rotation is done by and silencing some parts of the machine depending on an extra encoder, like this 3-part Für Elise music box.

Hole-Plate(-strip)
A different method would be to encode the music as holes in a continuous strip and use air as a decoding method. If the air then gets directed into pipes, we have a street organ. Typically, one would use a paper strip as the encoded message, but it could be printed just as well, especially if one uses a setup that uses plates hinged to one another instead of a rolled-up paper as in this example. With such a way to stash away the extra length, the upper limit for music length rises from a couple of seconds to several minutes easily even with such a "bad" encoding.

@Trish Thanks. I know a little bit about sound. I'm talking about taking an actual recorded sound, any sound, prerecorded and printing out the wave lengths to make a physical conversion. I know it would be a very short sound. I'm thinking trenches.

@1.21gigawatts recorded sound itself is not printable. What you see on your sceen is not sound it is the graphical representation of the mathematic analysis of the physic measurement made by the microphone. It is a representation of the instructions to a physicist "mix these vibrational patterns to create this sound". You can print a device that creates vibrational patterns - like a music box - or a mathematical representation - like a graph of the fourier analysis - but you can't print a vibrational pattern itself.

@1.21gigawatts added more about the limitations of peg encoded and found a way out to get pretty much an arbitrarily long and complex piece of music provided one has the fitting decoder machine.

I think this is just about doable. In this answer, I will assume you want to produce a "rumble strip" style of object that will reproduce a recording of human speech. I'll assume you don't care about sound quality, you just want the words to be intelligible.
The main things to consider are the printer's resolution, the size of the object to be printed, and the sample rate. Together, these factors determine the length of the sound, and the rate at which you need to move along it to reproduce the sound.
Let's start with sample rate. A CD has a sample rate of 44100 samples per second (Hz), but that might be a bit ambitious. Telephones use a lower sample rate of 8000, and it says here that speech is still intelligible at a sample rate of 2500 Hz. Let's go with this rate.
Now let's consider the resolution of the printer. A typical nozzle size is 0.2mm, which probably limits the resolution to around that size, though you can probably do better with some care, and I imagine people in this community will be able to help with that. I am guessing that you would want to print the object horizontally, so you're dealing with xy resolution instead of z resolution. (Note that resin 3d printers have much better resolutions, so they might be ideal for this task, despite their smaller print volumes.) Let's start by assuming 0.2mm is our resolution, since this should be easy to achieve with any printer.
This means that every sample in the sound file takes up about 0.2mm. Let's say we have one second of speech - that's long enough to say "Hello!", for example - at 2500 Hz. That means we have 2500 samples. 2500 * 0.2mm = 500mm, so your rumble strip will be about 1/2 meter long. That's unlikely to fit on your print bed, but you can print it in sections and stick them together - you can probably print them all at the same time. You could even curl it round into a spiral, making it even more like a vinyl record.
Then all you have to do is take a rigid object like a guitar pick and slide it along the strip at the right speed, so that it takes about 1 second. Then you should hear the sound played back. Attaching a resonator to the pick or the strip should increase the volume.
Increasing the resolution will decrease the length of the strip, or allow you to play a longer sound for the same length of strip, or increase the sample rate. E.g. if you can get a resolution of 0.1mm then you could play a 2 second sound instead, using the same 0.5m length of rumble strip.
In principle, creating the object is not hard, but I don't know any software that can do it out of the box. You just need to make the surface height correspond to the waveform. If I was doing this I would probably write a Python script to turn the wave file into a list of numbers, then paste those into in OpenSCAD's polygon function, which I would then extrude to make the object. But others might know an easier way.

This is just beautiful! I was playing with the idea to generate gcode, but openscad sounds like a great idea. I guess that some simple 8-bit tune (commander Keen, super Mario) could be encoded in even less samples per second and a second of "music" might fit on a 20cm. strip.

Here's an alternative which takes advantage of the relatively (!!)  high-precision layer capability of the 3D printer:  Make a lithopane strip and use an optical sensor to reproduce the sound.
This is (was) done to encode the soundtrack for movies alongside the image frames in the film strip (reel).  Basically the thickness of the print at a given location modulates the optical throughput and thus the signal strength out of the photodetector.
Note that, as with movie reels, you will need a lot of real estate to record a decent amount of audio.


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XYZPrinting Premium Metallic PLA Conductivity
I have a XYZPrinting Da Vinci Mini W+ that I got for last Christmas. I am looking at the filaments available for it, since the included PLA is running 'low' (according to it) at 21 metres remaining. The one filament type that interested me the most is the Premium Metallic PLA. My question, that the website doesn't seem to answer, is how conductive is this material? Does it have any conductivity that would make it realistic to use to carry a current from something like an Arduino or Raspberry Pi, or is it too insulated, meant to only look metal, to act as a conductor?
Why I ask (Background - Not as Important)
I ask this, because of an idea I had. Printing a pretty low quality PCB type circuit. Instead of being forced to keep my circuits on breadboards with wires jumping from here and there, I would take a conductive layer and sandwich is between to insulating layers. If I wanted two trace layers, I'd do the following pattern (with I being insulating and C conductive) "ICICI". Since I only can print in one filament type at a time, I'd print each layer in the thinnest thickness (1 micron, I believe), and have to fuse them together. I could do this in a few ways, using glue of some sort, or a hand-help filament pen to fuse the layers from the outside (the conductive layers would be slightly smaller, of course).

Most PLAs are non-conductive: they contain little to no metal in comparison to plastic and can't make a conductive path. Even metallic PLA does not contain enough metal to be conductive.
There are some rare filaments that are conductive, they are sold as conductive PLA. I have yet to encounter a non-black conductive PLA.
One filament I suspect to be possibly conductive but have no hard evidence is made by The Vitual Foundry and contains about 80% metal. It is intended to be treated in the oven to burn out the plastic part, leaving behind a somewhat pure metal structure, but might be conductive without this process already. I have no experience with this and all my exposure to it was this answer. It should be highly abrasive though.

Ah. That's too bad. Thanks for the answer then. I wasn't sure, because I'm relatively new to this. I knew PLAs themselves weren't conductive, but then I saw it said "copper" as the material, and I thought to myself "Hey, isn't copper the thing that is used as wires?" and just wanted to check. They don't actually list any conductivity information (which is kinda dumb IMHO, since some applications actually need that info). Again, thanks anyways.


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Combining multiple STL files
I have a collection of STL files, each containing a separate moving part of an object I want to print. (Imagine a set of gears, or similar, that prints as a single object with multiple moving parts.)
My plan was to import them all into Cura, then hit print, then take my fully assembled object off the build plate. However, Cura ignores the coordinate system in the STL files and automatically separates the components from each other on the build plate. This is usually helpful, but it isn't what I want in this case.
So I'm looking for a quick and simple way to combine my multiple STL files into a single STL file. I know that the objects don't overlap, so I don't need to do a CSG union operation - it's enough just to concatenate the objects.
I tried OpenSCAD, which works, but it takes a really long time, because the meshes are fairly complex and it does the full Boolean operation. Is there another quick and simple way to perform this task?
I'd prefer a command line utility, but I'd also be happy if there's a quick and simple way to do it in some free graphical software. (However, I don't want to spend time manually positioning the objects - they're already in the right places in the STL files, so I just want to import them and go.)
Edit I've accepted Trish's answer (use Blender), but I'd still appreciate a command-line option if anyone knows one.

How would you expect the 3D printer to print the parts movable and at their position at the same time? If they are not placed on the build platform there will be a lot of support needed.

@KlausD. they are all in contact with the build platform and none of them have overhangs that would need support. However, they nevertheless interlock with each other in 3D space in such a way that they can't be separated.

(If that sounds impossible, imagine that one object is an hourglass and the other is a torus that surrounds it, with only a small gap between the inner surface of the torus and the neck of the egg timer. Both contact the build plate and no overhang is more than 45 degrees, but the hourglass can't be removed from the torus.)

@Pᴀᴜʟsᴛᴇʀ2 exactly that. But with the important provision that I know the parts don't overlap, so a Boolean union operation isn't needed.

It is funny you ask about this ... Koenigsegg has to 3d print the turbochargers for his ultra-supercars called "One:1". Can it be done, yes. I'd bet it lends back to how it's designed more so than how the print is setup after design.

@Pᴀᴜʟsᴛᴇʀ2 it's abut how the file is stored.

It's trivial to position separate objects in MeshMixer and export the result as a single STL.  I think you're trying to force a square solution into a round hole

@CarlWitthoft the objects are positioned already, just in separate files, and the idea is to not need to reposition them. No square pegs here, just a beautiful round one produced by homegrown C++ code, which needs a little polishing before it will fit.

(Well, to the extent that using a C++ library with overly restrictive I/O possibilities is a square solution, I agree that's the case here. Please take that up with the authors of CGAL, not me. It may be a square solution in that respect, but it's the only viable one in my case.)

What you try to do is called "Print in Place". However, it is not done by importing several STLs one after another as cura does remove the origin and recenters each imported object upon importing. However, an STL file can contain more than one body.
To generate a PiP model, you need to export your whole project as one STL file containing all the parts and then Cura not only doesn't rip the model apart, it can't do so.
Workaround
If you can't export the whole project in one piece from your design software, you could use a workaround by importing it into a software that can export as one item. Among these is blender, so importing all the parts into blender and then exporting the whole project as one STL is a simple fix. Other options would be TinkerCAD or Fusion360.
The Step by step guide for blender is simple and the general idea of this workflow is the same for other options:

Open blender
New project
delete the cube via entf + enter
Get the files into the workspace via either:

Drag & Drop

File > Import > Stl (.stl)
select the file + enter

Possibly reposition the object, till it is in the right position
Repeat 4. to 6. till all parts are imported
File > Export > Stl (.stl) + enter

My issue is that the program I'm using to create the objects is not able to export them as a single file, but only as separate ones. They do indeed need to be in one single STL file, but the question is about how to do that, given that the program will always output them in separate files.

Which program? Fusion360 can export a whole project.

I wrote the program myself. The C++ library I used does not have the functionality to put more than one object in an STL file.

@Nathaniel then you might want to combine via blender by just importing all before exporting.

Thanks for the edit. (+1) I'm not a blender user, and it is quite a complicated program - if you have time, step-by-step instructions would be super helpful.

@Nathaniel the step by step is simple and added.

another option is to import them into Tinkercad, position them, export all in one group. Tinkercad is free and substantially less complex than the magic of Blender

@Trish cool, that worked, thank you. (I didn't need to reposition them, as you said, it respected their positions in the original files.) The only disadvantage is, Blender for some reason uses its own special file dialog, which uses different conventions from my OS and is therefore mildly painful to use. However, I found I could drag to select multiple files, and thus avoid importing them one by one. I'll accept this in a day or two.

@Nathaniel Just came back to this question as I was looking for this workflow to link to, thanks for choosing your preferred workflow!

The operation you want is almost just cat'ing the files together. However you need to remove the 80 byte header from all but the first, and add up the 32-bit triangle count from each file immediately after that. Output should be:

Copy of first 80 bytes of file 1
Sum of int32 from offset 80 of each file.
Bytes 84-end from each file.

See https://en.m.wikipedia.org/wiki/STL_(file_format)

Similarly to @R..'s answer, you can easily concatenate the contents of each file if you have ASCII .stls.

Make sure the .stls are in ASCII format: Open them in any text editor (like Notepad++). If it's readable, you're fine, proceed to (3)
If not readable, convert them to ASCII .stl format using a converter tool (like this)
Open each ASCII .stl file
Copy together the contents of the files, except for the "solid" and "endsolid" statements where the files meet

They're binary unfortunately. I'd have written a Python script to concatenate them otherwise. Sorry to be awkward!

Import them to Tinkercad and then output your combined file from there. You can go into Tinkercad and on the top right side you will see "import", click that to import your file (you can repeat the process as desired) and it will put the files on the workspace .. on the screen. When you have your workspace all set the way you want select them all the click "export" and it will export all of them to one file for your use.

Hi Nate and welcome to 3D Printing.SE! Please expand the answer how one would do that, this is too short for an answer.

My response has been edited per your request.


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Makerbot Replicator 2X - restarts after heating
Really need some help. Let me run you through as much as possible.
I have a Replicator 2x. I've owned this for around 2 weeks now (used). after some teething issues I've been printing really well all week.
I left a print for the first time to run on its own and when I returned it had stopped after approx 10 % was still on and on the main menu screen.
I removed the partial print and, since then, when I go to print or preheat it will reset near the maximum temperatures (230 °C extruder and 110 °C platform). Individually setting these, all achieve desired temperatures, and filament change still works.

I swapped the left-hand-side (LHS) extruder parts for the right-hand-side (RHS) and tried a reprint, same result.
I swapped the wiring at the board to use the LHS extruder wiring for the RHS. same.
Disconnected the stepper motors and same issue.
Reinstalled firmware; same result...

It was running the MM2X (dual extrusion) upgrade, and I was supplied with the original extruder and thermocouples, spent afternoon swapping and this has the same issue.
By reset, the whole unit goes dark (LCD and LED), beeps and back to main menu.
It works with the bed unplugged, or the extruder heater unplugged, but not with both plugged in. Heard this being called brown out.
I'm guessing its the Mightyboard or the power pack. All lights are green on the board during running. I have a multimeter and can test the board if known values or a guide location is available.
Any help would be great, pulling my hair out.

"Im guessing its the mightyboard or the power pack."
Right track there.
Usually this symptom suggests your heaters are overtaxing your power supplies.
Since you swapped extruders already, the heating elements and sensors in those are not likely to be an issue.  That leaves the bed heating element and power supply.
A resistance measurement can help rule out the bed heater but since it works without the extruder, its probably not a severe issue there.
If I had to guess, I'd say power supply.  If you can, rig up a meter to measure its output and cause the issue.  If the voltage drops drastically in tune with your screen going dark, try to replace with a beefier (higher amperage) one.


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PLA Filament Not Softening During Load w/ FlashForge Creator Pro
Recently, after printing fine for several weeks, I've gone to load in white PLA filament into the right extruder on my FlashForge Creator Pro and the extruder is not pulling the white PLA filament through. The gears grab the filament and pull it down but it never makes it out the other end. I have successfully used this filament through this same extruder as recently as yesterday. The steps I have taken are:
• Remove the extruder motor and cleaned the gears. There was no noticeable issues or clogs.
• Turned the heat on and used the skinny metal unclogging tool that came with the printer to drive any excess filament out of the nozzle.
• Removed the nozzle and cleaned as best as I could. To be clear, this does not appear to be a nozzle clog because I have removed the nozzle, leaving the plastic tube that's under it in the extruder and I can run the unclogging tool all the way through the tube and out the top of extruder when the nozzle is not on. The line appears to be clear.
• I then tried to load the filament without the nozzle on (but with the plastic tube still in the extruder; which I confirmed in the last step does not have a clog in it). Same problem.
• I unloading the black PLA filament from the left extruder and then took the white PLA filament (which wouldn't load into the right extruder) and tried to load it into the left one. Same problem. I then took the black PLA filament and went to load it back into the left extruder and it worked fine.

The white filament seems to be the problem but I cannot figure out what the problem would be. It's the same size as the black filament and the black filament works fine through the extruders that the white one does not. As mentioned, this filament worked fine yesterday.
I took the fan off and watched the filament get gripped by the motor gears and pulled down until it is entered into the hole below the motor. That is the point at which is gets stuck. It appears the filament simply is not being softened/melted enough to start feeding through the smaller hole.
I researched this and saw that this could be the result of a faulty reading by the machine due to thermocouple problems (?) but it seems doubtful now that I've tested successfully with black filament.
My settings are as follows:
FlashForge Creator Pro
PLA Filament
Extruder - 210C (I started a 200C but then increased)
Any thoughts or pointers would be great. Thank you!

After all of this trial and error it was a simple solution.
I did not snip off the end of the filament after unloading. The filament had been tapered after unloading because of the way it was extruded previously. I don't know exactly why (please feel free to add to this answer) but when I made a clean cut on the end of the filament and then fed it through, it extruded with no problem.

Fresh filament has a diameter of around 1.75mm, while the inner diameter of hot ends and especially bowden tubes is a bit larger; for example, Capricorn is specified at 1.9mm.
If the end of the filament was heated, it starts to adapt to that larger diameter whereever it's warm enough to be malleable. When removing the filament, that doesn't prevent removal: It's still warm and easily removable. Once it's cooled down, though, that extra diameter adds a lot of friction when trying to feed the filament back into the hot end.

Atop @Towe 's comment: The molten plastic gets compressed by the plastic following, thus creating the pressure that ultimately creates the extrusion. However, the tubing is slightly deformable, so that when the filament cools and solidifies (with a little bit of shrinking) it still sits tight in the now no longer "stretched" tube.


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CR-10S Pro pausing and starting again
I found this question, CR-10 randomly pauses for a few seconds, that someone asked earlier. I am experiencing the exact same thing, only on a CR-10S Pro.
None of the suggestions on that post helped. For what it's worth, I am using  Ultimaker Cura 4.3.
Any help would be wonderful!
I made this video for someone I know from Creality. The pausing seems to happen at each new layer. But, as the layers pass like 4 layers then the pausing stops. This also happens on every print big or small. I changed nothing and it just started happening.

Quoting my comment from the previous question:

I am seemingly having the same issue only on Cura 4.3. There is no
  "Maximum Z Speed" anywhere on 4.3 so how can I fix this? As talked
  about above I just checked my "minimum layer time" and it is set to
  10. I have also used another slicer and this same issue keeps happening it just messes up differently. I've also tried printing from
  SD card and OctoPrint. Same issue... How could this be my slicer if
  this same thing is happening on a different slicer than Cura?

Hi Matt, welcome! Could you please give some more details when the pausing happens. You can also post a video or a link to a video for others to help you out. E.g. setting "minimum layer time" may have an effect in this when the layers become small (in printed square mm). So, when does it pause exactly?

The additional video is great, Matt. We have recently added YouTube video support to our SE.3DP posts, so you can edit your question to include the URL and others can view it on the page, without having to visit YouTube externally. In fact, all additional information should be edited into the question, and not put in comments, as comments tend to be ephemeral in nature and get deleted over time, hence why I edited in your related comment (on the link question) earlier.

I tried to give the answer but it will not let me so I guess I will keep it to myself. I fixed it. I am also leaving because I am getting corrected over and over instead of getting help from admins. It would be cool if there was help for my issue along with the help navigating this website. Thank you for those that tried to help

From your comment on the linked question you state:

As talked about above I just checked my "minimum layer time" and it is set to 10

Note that Cura's default value is 5 seconds.
This means that the print speed is lowered down to the minimum print speed to have layers that print for at least 10 seconds. When it cannot print slower (there is a minimum print speed) and the minimum layer time has not been reached yet, the print head halts until the time value is reached, then it continues. This behaviour is expected when the print area becomes small so that the time per layer drops under the 10 seconds.

The minimum layer time was 10, not 5. I just installed 4.3 to try and fix this issue and changed nothing. So, are you saying the minimum layer time default is 5 or are you saying minimum print speed default is 5? On 4.3 there is no "minimum print speed".


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Bumpy first layer with PETG
When I print with PLA, I get a perfect first layer.
However, when I print with PETG, the first layer looks like this:

I've read all the info that suggests reducing the temp, speed, and increasing retraction... I've done all that which has improved things a lot, but I still get this... I can't seem to work out what's causing it.
How do I get a perfect first layer with PETG?
The latest settings that I've tried, and produced what you see in the picture are, using Cura 4.3 standard Dynamic Quality 0.16 mm profile with these tweaks:

Temp: 220 °C
Bed: 65 °C
Retraction Distance: 10 mm (not that this would have any bearing on this flat first layer)
Print Speed: 40 mm/s

One thought I had, does PETG need a different clearance between the nozzle and the bed than PLA?

@0scar I thought the ° symbol was the exception, along with ' and " ?

Ah no, you're right... ° " ' are only no space if it's used in coordinates, not temp.

One thought I had, does PETG need a different clearance between the nozzle and the bed than PLA?

Short answer: "Yes, for some it does".

The results from your image are typically seen when the initial layer height for PETG is too small. PETG likes an additional gap on top of the usual that is used to print e.g. PLA.
For me personally I don't experience this general consensus (I've printed kilometers of PETG filament at 0.2 mm initial layer height at a glass bed with 3DLAC spray without any problems), but it is well known that if you print PETG (and if you experience problems) you need to increase the gap between the nozzle and the bed. From "PETG Filament - Overview, Step-by-Step Settings & Problems Resolved" posted on rigid.ink, you see that they (usually) advise an additional 0.02 - 0.05 mm gap:

Bottom line, if the normal gap doesn't work for you, increase the gap to see if that works better. Note that in some slicers you can add an offset in the slicer so that you do not have to do the releveling with a thicker paper (or if you are using auto-levelling). E.g. in Ultimaker Cura you can download a plugin (for recent Cura versions from the marketplace) from user fieldOfView called "Z Offset Setting" to get the Z Offset setting in the Build Plate Adhesion section. You can also do a little trick in the G-code by redefining the height so that you can put this in a PETG start G-code or something.

I don't think this is the problem in my case, I've tried increasing the gap, but then the filament doesn't stick to the build plate. Initial layer height is 0.16 mm.

@BG100 That is low for PETG, please use at least 0.20 mm, or a little more (0.24 mm or so).

Wouldn't an increased initial layer height make more sense? Adjusting the offset will necessarily give wrong volume of material.

@R..Yes, that is what I do, but an increased gap is reported to work. I've printed kilometers of PETG filament at 0.2 mm initial layer and never ran into such problems but there is a whole community that swears by an increased gap. Note that the whole leveling procedure causes your nozzle to be not at Z=0 but at paper thickness, so that implies a volume mismatch also, still most folks do this cause putting the nozzle at bed level when Z=0 doesn't work well.

@0scar Thanks for your help. I actually gave up and switched back to PLA as I needed to get my project done, but I'll refer back to here when I try again when I've got some more time. I'm sure its just a case of tweaking the settings around z offset, layer height, speed, possibly esteps.

When I print with PETG, my bed is 80 °C for first 2 layers then I drop it to 65 °C
Extruder temp first two layers 240-250 °C and then drop to 225-230 °C.

Welcome to 3D Printing SE and thank you for your contribution. When you get a chance, please take the [tour] to understand how the site works and how it is different than others.

Hi, welcome! Please explain what the relation of your answer to the bumpy first layer is,. As the answer is now, it doesn't answer the question, you merely state your settings to print.


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What are the pros and cons of using a BLTouch in place of a limit switch?
This is about practicality. I'm hearing that people are using their BLTouch not to adjust the Z offset, but as the limit switch for the machine! Why is this so? What are the pros and cons of using a BLTouch (or any touch sensor for that matter) in lieu of a physical limit switch?
(NB: I'm looking for objective reasons, where no other solution will do as opposed to personal preference reasons where people just like to use it).

Touch sensors (or inductive or capacitive sensors) are generally used to probe the bed to determine the bed shape. For metallic beds that are not perfectly straight this works excellent. But, if your bed is straight and level (e.g. when you are using a straight slate of glass), you do not need to probe the surface as it is level. Instead you can use the probe to determine the Z level.

Pros for a limit lever switch are:

simple and cheap mechanical switch
no firmware changes necessary
no or few soldering
already present on most bought printers

Cons for a limit lever switch are:

needs fine adjustments counter part to work optimally
something can get in between the lever and counter part
it doesn't look cool

Pros for a more sophisticated sensor:

it can help with adhesion if the bed surface is deformed or dented
it looks cool
everybody is using it so it must be good

Cons for a more sophisticated sensor:

expensive and complicated sensor
requires firmware changes (e.g. sensor offset value)
requires soldering, or connecting more cables
inductive and capacitive sensor work usually better at a higher voltage
higher chance of malfunctioning (more parts and electronics)

"everybody is using it so it must be good" is not a valid argument lol. Nice try :D

@user77232 For many people that is actually true, but I was being sarcastic.

There's cost.
Or it might be fragility -- there is a little overshoot, i.e. the time between when the Z-stop sensor(whatever type) indicates zero is reached and when the stepper motor actually shuts down. The standard lever-switch has plenty of flexibility and "give" but the BL Touch may not, and may be damaged if the gantry tries to move a couple hundred microns past "true" zero before stopping.  I would be cautious, depending on your budget, about trying it out.

Isn't the touch sensor's trigger point under the stow limit, that means there is little more space left. This is also valid for the inductive or capacitive sensors, they do not touch the bed to trigger, so there is enough space for overshooting, if there is a substantial overshoot that is.

I would use both if I had a choice, but my stock "Melzi" board doesn't have enough inputs as near as I can tell. Most of the (scarce) instructions show to disconnect the Z switch and connect the BL Touch to the digital inputs in place of the switch.
I don't see any other connectors to wire up the EZ Touch to. Maybe the ICSP programmer, but I haven't messed around to see if that would be usable (nothing in the stock CR10 box is connected to it anyway).
So I think it's more of a practical issue that you use one in place of instead of adding.
However, less pedantically, why is a BL Touch better than a limit switch?
Two words: Auto Leveling
If you get everything setup right, auto-leveling should be great. I say "Should be" as I still don't quite have the board setup right. It keeps trying to push my nozzle into the PEI sheet, so I really DO wish I had both limit switches and the BL Touch.
Leveling on a hobbyist level 3D printer isn't that hard, but it's time consuming and requires some care. Having to do it every time becomes a colossal pain. So the idea that you could clean off the build plate, hit a button, and have the printer figure out what level was and just start printing is great. Not having prints peel off the plate because you had the gap set wrong, or didn't get the back corner leveled off, or the PEI sheet getting damaged because the nozzle ran into the sheet ... priceless.
But hey, if you're using a 3D printer where you'd even think about a BL Touch, you're on the DIY/Maker side, not the "stick in an SD card and hit print" side, so you should be used to figuring out how to wire one in. It's part of the adventure, right?

One other way a bed sensor may be preferable over a common limit switch: it automatically adjusts when you change out the build surface.
Most glass build surfaces are anywhere from three to five millimeters thick, while the surface they replace (texture coated or uncoated fiberglass/resin, magnetic sheet, etc.) are around one to 1.5 mm thick -- that's a enough change in build surface height to be near the limits of the bed adjustment on my Ender 3, for instance.
There are ways to work around this, for instance with spacers that clip onto the bottom of the X gantry to trigger the Z-stop at a higher position -- but if you forget to install the spacer on a build surface change, you may end up scratching the coating on your glass bed (probably a bad thing) by dragging the nozzle across it, as well as potentially damaging the nozzle (cheap, but takes time to replace once you figure out why your prints are suddenly failing).  If you're using a bed sensor in place of a limit switch, this oversight can't happen, because the Z homing will automatically detect where to stop regardless what you've mounted on the bed.


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Why does hairspray work as an adhesive for ABS?
Since I have a 3D printer, I worked primarily with printing ABS. I tried multiple methods for adhesion (various soluble glues, ABS juice) but always had the most success with hairspray on clean borosilicate glass, as long as I print with a bed temperature above 75 °C and inside an enclosure.
So I wonder, if it is known, why and based on which chemicals the hairspray method works so well?

Hairspray is not ABS specific - it is just in need of a very strong bond.

First of all, not all hairsprays work. The chemicals in hairspray that causes the bonding is "VA/Crotonates Copolymer", it is also called "vinyl acetate/crotonic acid copolymer". Most commonly known as PVA, which is also a filament used as water soluble support material. This is a synthetic polymer created from monomers.
When heated to a certain temperature this ingredient becomes sticky, this makes the filament stick to the plate. It is the double bonded Oxygen molecule that makes this happen. This is not only present in chemicals you put onto the bed, but also the chemistry of certain bed materials. Quoting our own Ryan Carlyle from this thread, A replacement for Aquanet Hair Spray?? Wolfbite by Airwolf:

Most of the popular build surfaces have very similar underlying chemistry. That's because they all rely on diffusion welding for adhesion. The molecular chains at the interface slightly dissolve into each other.
Gluestick active ingredient - http://en.wikipedia.org/wiki/Polyvinylpyrrolidone

Aquanet and liquid PVA glue active ingredient - http://en.wikipedia.org/wiki/Polyvinyl_acetate

If you're familiar with organic chemistry, what you see here is an identical polyvinyl backbone chain, and functional groups that both have a ketone/ester double-bonded oxygen adjacent to a space-filling component. (The space-filling component probably decreases adhesion so the print can be released.) And guess what? Permanent build plate surfaces rely on the same underlying chemistry:
Lexan also has exposed double-bonded oxygen on a polymer backbone: http://en.wikipedia.org/wiki/Polycarbonate

Kapton also has exposed double-bonded oxygen on a polymer backbone: http://en.wikipedia.org/wiki/Kapton

Acrylic also has exposed double-bonded oxygen on a polymer backbone: http://en.wikipedia.org/wiki/Poly(methyl_methacrylate)

PET also has exposed double-bonded oxygen on a polymer backbone: http://en.wikipedia.org/wiki/Polyethylene_terephthalate

Now, if you look at some common solvents for filaments, what do you often see? Double-bonded oxygen on small molecules. Here's ethyl acetate (dissolves PLA) and acetone (dissolves ABS):

These molecules are still diffusing into the filament polymer, but they're so small and mobile that they are able to completely liquefy and dissolve the plastic.
Isn't chemistry great?

Isn't PVA what's in common white school glue (Elmer's in the US)?

@T.J.L.Yes, white wood glue and white school glue also contain PVA (polyvinyl acetate), it is a PVA dispersion in water.

Very old article (comparatively) I know, but there are two plastics called PVA. Polyvinyl acetate, the glue, and polyvinyl alcohol, the dissovable-in-water filameant. Very different beasts.