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How to smooth PLA Prints without using sandpaper, solvents or paint
I need to smooth some prints with silk PLA filament.
The silk PLA has a nice translucent effect but unfortunately if sanded results in an horrible matte finish regardless the sandpaper grade (I have tried with many grades).
Since I don't have specific solvents or special equipment, and I don't want to paint it as well, I'm wondering if there are alternative ways to smooth the surface.
(Also a my friend speculated about some heat treatment with hair dryer... never heard of something similar and I'm not sure if this could make sense, and in case how should I try).

I've had great results with gold silk-like PLA filament, using varying grades down to 12000 micromesh (wet sanding). It's a bit of work, but the stuff shines beautifully.

some parts can buff up nice in a rock tumbler, if you know how to pick grit...

tempted to rate "+1 Funny" -- think about it: you want to remove or fill material without removing or filling material!  In all seriousness, as fred.u suggests, get a finer mesh polishing paper, or rouge cloth.

Unfortunately, there is no way to smooth PLA without sandpaper, solvent or paint - but you can fix the finish after sanding.
If you heat the plastic after sanding to just the point the outer shell starts melting the horrible matte finish goes away and the original color of the plastic returns.
You have to heat the plastic and then remove the heat source just as it's start melting (right before the original color returns, so when you see it working it's too late) because otherwise the object will deform.
I use a heat gun set to 180C and work quickly in short bursts, an hair dryer is probably nowhere as hot, so it will take longer to heat the surface.
You have to do this after sanding, applying enough heat to smooth the layer lines will just cause the object to melt and deform.
Try on a few failed prints first, you will need to get the feel for when to stop heating and you will still probably ruin prints every once in a while.
Another option is to coat the object in an epoxy that will hide the layer lines the best known brand for this is XTC-3D.
If you do decide to paint, you get extra thick primer that's supposed to fill the gaps between the layer lines so you don't need to sand as much (sorry, can't remember the brand name)

I don't think most hair dryers can melt PLA. They just take it over glass transition.

Use a heat gun instead of a hair dryer, as shown here - same principle, although this is on ABS.

Hair driers aim for about 60 °C


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Partial underextrusion in walls
I'm facing weird "pillars" of underextrusion on outer walls of my XYZ test cube.
On the pictures below I`ve printed PLA test cubes with a 0.4 mm nozzle, 0.2 mm height and 210/50 °C hotends/bed temperature.
Gaps are appearing in walls parallel to both X and Y sides. The pictured side is parallel to Y face.
I'm slicing with Cura, my printer is a homebuilt around Anycubic Kossel with Marlin 2.0 onboard.
What have I tried already:
1. Temperature from 190 to 210 °C
2. Retraction from none to 6 mm 60 mm/sec
3. Tuning down Jerk in Marlin from [10,10,0.3] to [5,5,0.3]
4. Tuning down acceleration from 3000 to 1000
5. Tuning print speed from 60 to 30 mm/sec
6. Checking belts, nozzle and extruder.
Now I just ran out of ideas. Delta is calibrated by G33 autotune. Mechanics looks just fine. What am I missing?

UPD1: tried removing combing - it did not help. But I noticed that my printer accelerates strangely at this parts
UPD2: could it be stuttering? I have 320 segments per second with block buffer size of 8 bytes(?)
UPD3: lowering segments count to 120 and raising block size to 32

Welcome to 3dPrinting.SE! Could you help us out here and orient the print for us? What side exactly are we looking at in the images? Being specific about which direction the print is printed in (ie: X/Y/Z axes) will help in the diagnosis.

Are you sure it's actually underextrusion? It looks like the bulges in your walls coincide with where the infill lines hit. Is it possible that you have too much play in the delta mechanisms such that these lines overshoot from momentum of the head?

Not sure about the extrusion, actually. I've checked the play and the head stands still.

Well, I could not track the problem and it lasted till two major updates:

I have changed rods for ones with proper lenght
I have reset all Cura settings to default

Localized underextrusion usually means you're oozing material somewhere it wasn't supposed to go. Since you have Marlin 2.0, linear advance might help solve that, and in general right retraction amount is important and turning off combing may be needed (combing over infill allows material to ooze).
Also there are reported bugs in Marlin 2.0 such as  https://github.com/MarlinFirmware/Marlin/issues/15473 that might be related, though I would think you'd not be using junction deviation since it's supposedly incompatible with deltas.

Thanks a lot! I'll try to tune Linear advance and combing.
Yes, I'm using classic jerk as it is required for deltas

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Is there any way to correct uneven bed temperature?
I'm using an Ender 3 Pro with stock heated bed & glass build surface on it (without any base of stock magnetic plate). My heated bed looks completely flat too despite of many uneven Ender 3 heated beds around.
But when bed temperature set to 70 °C and I check the temperature of bed with infrared laser thermometer gun, the front of the bed is around 72 °C and the back is around 64-68 °C. So the temperature is different at all sides and this looks like leading to warps too.
Is there any way to make it more even for all bed surface?

you can add insulation to the bottom of the bed. My CR10 had some, but it didn't go to the edges, so the edges would sink heat away and run cooler. I just stuck old double-stick foam on there, but there's kits you can buy. My DIY fix killed more than half of the diff, so i was pleased. It also helps just to pre-heat the whole thing longer to allow temps to stabilize deep in the mass.

I guess the tradeoff is the more you insulate the bed the slower it will cool down.

I had this exact issue with my Qidi X-Plus. After checking with a thermometer there was a spread of 9°C - enough to burn in (always the same) certain areas when printing at higher extremes of temperatures, or causing poor adhesion in other certain areas at lower temps. Very similar scenario too, I noticed this primarily when switching over to glass from the stock magnetic plate.
My solution was quite straightforward - I set the bed temperature on the printer's control panel and preheated it before sending it a print. As long as I left it there for a solid 10 minutes after getting up to temperature it balanced within around 1°C. I observed far more consistent results from print to print.
Now I don't know your exact machine myself, so I don't know if this is possible on the control panel on an Ender 3. However if it's not, as an alternative possibly consider looking up how to stick a pause in the initial gcode in Cura to see if you can achieve the same effect.

Great tip!  Tried it on my E3, got a smooth first layer.  Thanks!          Control, temperature, bed

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What causes my Bowden tube to melt on the side?
I run a 3D printer farm and I have to replace my Bowden tubes on the printers after about a month or two of use(roughly 1000 hours of use). The Bowden tubes continually melt on the side of the tube very near to where it pushes against the nozzle. I am running Ender 3 Pros and I run at about 205 °C with PLA. The Bowden tubes I have are some I found on Amazon and they are not Capricorn tubes.

EDIT1: I have added more pictures below of a new failure. This time you can see the marks of the teeth of the coupler a good inch below the failure point.

Melting is virtually impossible, that happens at 327 °C. To me this looks more like wear.

Hmm, so you're saying that wear caused a tear in the tube?

I'm saying that it cannot be melting caused by heat of printing PLA :) It looks as if it is wear. What other failure modes are possible?

After a lot of hard work and months of replacing and inspecting this issue I realized what's going on. The bowden tube gets soft as it gets hotter and hotter which allows the filament which is being extruded and retracted at a high speed to wear down the side of the tube. After some time the tube gets stretched out and it will eventually tear and that is seens as the hole in the pictures I provided. The solution to this problem is to upgrade to an all metal hotend, instate less aggressive retraction settings (which is what I did), or closely monitor your prints and replace your bowden tubing when it does eventually get  damaged (which I also do).

That may have sidestepped your problem but it's not "the solution" and has lots of tradeoffs. It sounds like the underlying problem was a fake Capricorn that's not even really PTFE.

@R..GitHubSTOPHELPINGICE I'm afraid I purchased the Capricorn PTFE from Amazon  so I would assume it is real Capricorn tubing however, the detail about the PTFE getting soft as it gets hotter is information I got directly from Capricorns website so I am unsure as to why you think it's not real PTFE. I would like to point out that this kind of wear on the tubing is after hundreds of hours of printing so I am not sure what you mean by "lots of trade offs" I have found that less aggressive retraction has decreased my print times.

That's why it's called a tradeoff. Faster prints, but wrong extrusion (material oozed in wrong place) leading to weak and ugly parts. Other tradeoffs too.

You assume that there is material oozing but there is no such thing. I assure you I never said that  I was getting weak and ugly parts after this solution. I would appreciate it if you could elaborate on these other trade-offs because this solution I presented is working quite well for me and the 20 machines I run it on.

If the tube is PTFE, the tube is not likely to be melting unless your hotend temperature is out of control.  You would probably notice the PLA cooking.
So, perhaps they aren't PTFE, or perhaps it is wear.
If it wasn't PTFE, you should be able to tell by the texture, slipperiness, and bending force.
The four thinned faces look like they would correspond to four of the barbs in the connector.  The thinned ring below the four thinned faces look like a wear line where the tube is pressing against the exit of the connector.  It looks to me as if the tube is moving or flexing in the connector.  The barbs act as little chisels cutting into the tube, which is how they restrain such a slippery material as PTFE.
It might work better if the tube were a little longer.  This might reduce the forces at the limits of movement which may be placing strain on the tubes.  If you can, you might also fashion a strain relief for the tube so that it doesn't bend right as it exist from the connector. If you can cut down on the movement, you will help with the external wear.
It is also possible that the tubes are being strained by a high filament pressure.  All the drive to push filament into the hot end is matched by an equivalent reverse pressure from the tube onto the connector.  If you can stand a higher print temperature, the life of the tube may be increased.
@towe added a comment:

I don't think those are marks from the teeth of the pneumatic coupler. The questions states "where it pushes against the nozzle", and the Ender 3 Pro seems to have a hot-end where the Bowden tube reaches all the way through the cold end and heat break to the nozzle.

A mechanical drawing of what may be a MK-10 hot-end as used on the Ender 3 Pro also suggests that the Ender 3 Pro has a PTFE lined hot end.  Lets accept that drawing as confirming that @towe is right.  Never-the-less, the marks you show in the photo look like the types of cuts I have seen from a pneumatic coupler.  How can we reconcile this contradiction?
The most direct answer would be that the tube is not reaching through to the nozzle.  In the photo you don't show enough of the blue tube to show the coupler scars which should be a little further up the tube.  Suppose that, in fact, the tube is not pressing against the nozzle.  This might not be the case if any of these are true:

There is a separate piece of PTFE that is permanently in hot end.
The Creality Ender 3 Pro looks as if
it is not configured for a Bowden feed.  A PTFE lined hot-end for a
direct extruder would have a piece of PTFE cut to length in the
hot-end.  A simple mod to make that a Bowden would leave that
sculpted PTFE tube in place.
The pneumatic couplers have been replaced.  Many couplers do not
permit the tube to pass through them, although the hole in the end
can be drilled to 4mm diameter.  In fact, preventing the tube from
passing through a pneumatic coupler is a feature in the intended
application of coupling to air tubes in moderate pressure
applications.
There is a bump in the path that is catching the  tube and
preventing it from extending through to the cold end and onward.

I don't think those are marks from the teeth of the pneumatic coupler. The questions states "where it pushes against the nozzle", and the Ender 3 Pro seems to have a hotend where the bowden tube reaches all the way through the cold end and heat break to the nozzle.

@towe, Thank you for your comment.  With your encouragement, I looked deeper and added more information to my answer.

I am afraid those marks are not from the pneumatic coupler, the gouges from the coupler are hidden just out of view by my thumb. I would take another picture and show you however I threw the piece away already. I know that the tube reaches all the way to the nozzle as there was no filament attached to the end of the tube which would happen as the filament approaches the nozzle and clogs any space between the nozzle and the tube end.

The Ender 3 Pro is designed with Bowden tube feeding in mind, it is a stock feature and there is one only one continuous tube from the extruder driver to the butt of the nozzle. The pneumatic couplers have been replaced but they are the type to allow tubing to pass through them.

@Daniel a remaining possibility,  unbolt though it seems to me, is that the tubes are melting.   If so they aren't suitable for the job.   When you have another failure, please take lots of close up pictures.   You could also try a melt test on the tube.   Put it in a 300°C oven for a couple of hours and check for any change or softening.   Maybe put a clip on it and see if the tube collapses.

This isn't melting, it is wear.
And it isn't typical wear you would expect due to abrasion.   It is wear caused by retraction.   As your filament retracts (usually between parts of the model to reduce stringing), the semi-molten filament is sucked back into the tube.
Then, when the filament is unretracted, the filament is pushed back into the nozzle.   However, in the meantime, a little of the filament solidified on the PTFE wall.   PTFE is very slippery, so the solidified chunk is peeled off the wall no problems - but it takes with it a tiny bit of the inside of the tube.
Do that hundreds of thousands of times, and the wall of the tube gets thinned at that point until it fails.
One solution to this is to reduce retraction.   Notice how the distance between the worn bit and the end of the tube is always the retraction distance in millimeters?
Another solution is an all metal hotend.
Or just trim your bowden tube shorter by a few mm every hundred hours of printing or so.


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Software to record hot end temperature?
Is there a software package that when I have my printer connected directly to my PC via USB could record and export hot end temperature data overtime?
Ideally this data would be recorded in a way that I could export it and manipulate it in the likes of Excel.
E.g. I see Pronterface has a temperature graph but it doesn't seem possible to export this. I know Simplify3D has a temperature plot in the machine control panel, anyone know if you can export from this?

I don't know if using OctoPrint is an option. If so, there is a plugin that claims to do exactly this. And you could probably find a few more if you looked for them. Note that I have no first hand experience with this plugin, but I can vouch for OctoPrint being convenient and by default it shows a temperature graph.
It might even be relatively easy to write your own plugin to accomplish this. This will mostly depend on your comfort with coding in Python/JavaScript.
As a sidenote: if your printer is connected directly to your computer via USB, chances are pretty high it is a simple serial connection. Having multiple programs use this connection at once is not possible as far as I know.
This implies that you will not be able to have your current software send it G-code lines while having another one recording the temperature values sent back from the printer.


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Weird deformities on surfaces with ender 3
Today I noticed some weird holes/deformities on the surface of this simple usb holder I printed. Since I'm fairly new to 3d printing I have no idea what may be the cause of this problem
My printer is a Ender 3 (Marlin 2.0.3) and I'm using Cura for slicing.
Pics:

It would be a great help if someone could give me some pointers on how to fix this.

Welcome to 3dPrinting.SE! I'm pretty sure this question has been answered before. You may want to search around the site a little bit and see.

Well, as I mentioned I'm new to 3D printing and searching is a bit difficult when I don't even know what the problem is called. I have seem plenty of posts on "blobs and zits", "under extrusion" and whatnots yet I couldn't find a similar distortion pattern. It would be really nice if anyone could tell me what I'm supposed to look for, give me a link to check or anything else...

Don't look at the patterns. These are warts. I'm betting the other question I posted as a duplicate might answer your question.

@Pᴀᴜʟsᴛᴇʀ2: I don't actually see any answer about the bumps/warts on the linked question.


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Cura projecting floating print onto build plate during slicing
I'm trying to do a multifilament print on my single extruder machine. So I separated out the models based on filament, and imported the parts into Cura. I ensured that "Automatically drop models to build plate" was disabled and in the "Prepare" phase that seems to work. However, when I slice the model it gets pushed back down to the build plate as can be seen in the picture below. Any recommendations? Do I just need to write a script to go in and shift the z location?

I've been playing with this and came up with a solution, so I thought I would share in case anyone else had this issue in the future. In Ultimaker Cura I enabled supports and z-hopping before I sliced the part, then I ran this Python function to remove the supports and get the extruder setup.
import re

def float_part(file):
    printString = ';LAYER:'
    partString = ';(.*?).stl'

    with open( file , 'r') as content_file:
        content = content_file.read()

    printArea = re.search( printString , content ).span(0)[0]
    partArea = re.search( partString , content ).span(0)[0]

    uncommentedLine = partArea - re.search( '\n.*?(?<!;)\n' , content[ partArea:printArea:-1 ] ).span(0)[0]

    lastExtrusion = uncommentedLine - re.search( 'E' , content[ uncommentedLine:printArea:-1 ] ).span(0)[0]
    secondLastExtrusion = lastExtrusion - re.search( 'E' , content[ lastExtrusion-1:printArea:-1 ] ).span(0)[0]

    lastExtrusionAmount = float(re.search( '\d+(\.\d+)?', content[lastExtrusion:] ).group(0))
    secondLastExtrusionAmount = float(re.search( '\d+(\.\d+)?', content[secondLastExtrusion:] ).group(0))

    ResetCommand = '\nG92 E' + str(lastExtrusionAmount) + '\n'

    with open( file , 'w') as content_file:
        content_file.write( content[0:printArea] + ResetCommand + content[uncommentedLine:] )


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Why is a mold required in isostatic pressing after performing Sintering
After an a object is formed through direct laser sintering, as a post-processing procedure the object is sent for hot-isostatic pressing, In hot isostatic pressing the sintered object is placed in a mold and then pressure and heat are applied.
I was wondering what would go wrong if the bare object without the mold was made to undergo pressing? Remember the sintered object already has a shape acquired during sintering so it may need a mold to get a specific shape during pressing. My assumption- In hot isostatic pressing the object might get softened and hence deformed due to heat and thus the requirement of a mold to keep the object firm. Is this assumption true??
And apart from deformation are there any other undesirable effects caused to the un-molded object during hot isostatic pressing?

It isn't done in a mold, not at the company I work. Very high pressure and temperature of an inert gas in a pressure vessel. We print in Aluminum-, Titanium- and Nickel based Superalloys. Note that it isn't that porous to change the dimensions drastically.

@0scar Is there any specific name given to the process


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Trying to remove autolevel from G-code - offset from bed not correct
I’ve been having all kinds of trouble with really every part of the print procedure on my Lulzbot Mini 2 that comes before the actual extrusion starts. I think I can get around 90 % of my issues if I just ran a level X axis at the start then input a manual Z calibration level.
I tried stripping out the nozzle wipe and autolevel commands from the beginning of the G-code but then the printer started the job about a centimeter above the bed.
Does anyone know how I can safely correct my Z-offset?
I'm currently using Lulzbot Cura but am planning to switch to Ultimaker Cura once I've got test prints going again.
Edit:
There is a z-offset that can be set using the physical printer UI but I suspect this isn't the setting I should be trying to alter as theoretically it should be pretty close to right since my vanilla Lulzbot Cura gcodes used to work and I haven't changed that value. Am I wrong on this?

Send M851 Z0 to reset the Z-offset, but I kinda get the feeling this isn't the offset you mean, or do you? Note to use M500 to store.

I can give that a shot, thanks! TBH I'm so out of my depth here I don't know what exactly I'm looking for and I dont want to setup a scenario where I accidentally gouge my print surface.
I just know that the extruder started printing waaaay to high after my change.

I think you are "asking for a solution" (you think that the auto levelling is your problem),  while you should address the original problem and describe what's wrong with the prints.

The original problems are many which is why I skirted around explaining them. I have a slight issue that causes my Y belt to skip on fast travels, my X bar doesn't stay level between prints, and the autolevel probe (which is the nozzle in the case of this printer) doesn't seem to be getting electronic contact with the leveling washers despite both appearing to be clean. I think the simpler solution for me at this point would be to live with all those issues but I can't get to the print step because the autolevel fails repeatedly until the printer gives up and halts.


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3d printer recommendations that can print fidgets?
I am looking for a cheap 3d printer that can print this: https://www.thingiverse.com/thing:1307100 and is hopefully under US $200, such as the Creality Ender 3, Monoprice Select Mini Pro and V2, the Wanhao Duplicator i3 mini, the Anet A8, or the tronxy p802ma.

Try looking for secondhand printers on kijiji or craigslist. I got one all assembled, and calibrated for less than half the retail price. It was used so little that it had the original filament that came with the printer. The previous owner basically bought it, set it up,  got bored, and sold it.

I'm voting to close this question as off-topic because it is a shopping question.

Pretty much any recent commercially available 3D printer should be able to print that model. Only really old stuff, or poorly built DIY machines, might have trouble. It may take some tuning of slicing settings to avoid problems with the rings bonding together during printing, but a more expensive printer is unlikely to make the tuning any easier.
The printers you listed in the question are probably all decent choices. I have an Ender 3 and like it but it's a little over \$200. There are some printers well under \$200, like the Monoprice Mini Delta, but I don't have any experience with them and product recommendations are off-topic here anyway. Also keep in mind that you'll have to spend a little bit on consumables, at least one spool of filament that's typically around \$20 (slightly cheaper for no-name brands, much higher for fancy color/shine/etc. or special materials, but simple PLA should be fine for what you want).


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Cura Filling holes from a model from Blender
I am Attempting to print this, from Blender

But Cura decides to fill in the middle part of the model.

I exported and imported the model from an STL file.
If anyone can answer this, that would be greatly appreciated.

Likely the STL file is not actually valid (doesn't make up a manifold). I'm not sure if getting bad STL files like that is a common issue that can happen with Blender; it happens with various low-quality tools.

:D there are faces inside the infill area.

Have you tried to heal your model in Meshlab, then save and import into Cura?

Nope, I've never tried Meshlab, never even heard of it until now.

Try disabling the "Union Overlapping Volumes" option on Mesh Fixes section. Worked for me.

I would recommend using an actual CAD/CAM program, such as Autodesk Fusion 360, instead of using a 3d model program. Not only will this be able to directly export you finished model to Cura, and the models are made in a way that works with a 3d printing slicer, there will be more help around 3D printing for it.
Although it is slightly difficult to use to start with, as you become more proficient, it is a very powerful tool to have. . Fusion 360 is free for hobbyists or students. See this link for help activating: https://www.autodesk.com/campaigns/fusion-360-for-hobbyists.
Another option would be SolidWorks, although you do have to pay for this option, but it is much simpler to work with in my opinion.

SolidWorks is so extremely expensive -- $4000+ USD -- that "you have to pay" does not really describe it.

Other free option that are easier to use for beginners: Design Spark Mechanical. Not as powerful though.

@Trish Thanks for suggesting that. I will edit my post and add it.

I've never had problems with models from FreeCAD, OpenSCAD, or QCAD, either.

@Davo I'll edit my answer later to include these suggestions. I first need to try them though just to make sure there are no problems, or if there is anything confusing about it. Thanks.


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Meshmixer size of model
I've created a model in Sketchup and exported the file as a .stl
Since the model is 80cm x 24 cm i need to cut it in meshmixer. But when i open it in meshmixer it appears tiny. Why doesn't it open as the real size?

it might automagically scale to the size of the chosen printbed, or it might be that the model actually is such tiny. It would help to have access to the model.

Perhaps you modeled it in cm, but most programs import in mm. The stl file does not include a scale, just a number of units.

You mention your dimensions in cm. Any chance that the STL export is also in cm where Meshmixer might expect mm?
Assuming your Sketchup template was set to cm:
To validate this guess you could measure/eyeball a known dimension and if that comes out to be 10 times too small you could scale your model by 10 times.
Alternatively you could adjust the template in Sketchup.
Additional information on STL files:
By it's very nature, the STL file format is just a bunch of unitless numbers in a well defined structure. This structure represents a set of points (vertices), lines (edges) and and triangular surfaces (facet). A few simple rules apply to exactly how all this should be defined. (See here)
But the key thing here is that an STL file is not aware of units, the program used to generate the STL file (e.g. CAD software) needs to be told what units to use, and accordingly the reading program (e.g. slicer) needs to use the same settings. Generally in mechanics applications we default to mm, at least in metric land. All this is explained a bit more verbose here.

Genius!! It worked perfect when changing to milimeters. But now the model appears outside and far away from box printer box (yes i am new to this)

Any chance you made your drawing offset  from the world zero? As in: where did you draw you part in Sketchup, at the origin or just somewhere else?
(Although you can change that in Meshmixer as well by using the align tool.)

The align worked. But the printerbed is not centered to the screen. It uses the center of the model (original zero)  so it becomes weird when I rotate the model

At this point I am a bit unclear on the specifics. What exacty do you need to accomplish in which software? I understand you design with Sketchup, and want to cut it up in Meshmixer. What slicer are you using. (Some slicer allow you to do the cutting part in the slicer as well.)

Sorry. I use Cura for the printer, it's a Ultimaker S5

Can you split the model in subparts and import those into Cura? From there Cura should put the pieces in the center and on the buildplate.


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Extusion rate limiting and firmware retract
One frustration I have with Cura is that it has no way to set print speed in terms of a volumetric extrusion rate, when extrusion rate is the main physical limiting factor for how fast you can print. It's a pain having to have different speed profiles for different layer heights (and doesn't work with adaptive layers!), different line widths, different materials, etc. I'd like to just set a feedrate limit on the extruder axis, which would achieve this and make it easy to switch already-sliced models between different materials. However, having a low extruder feedrate limit would make retraction and recovery from retraction incredibly slow, to the point of being unusable - since I've found quality so much better without combing, I now have a lot of retractions.
I'm thinking about building Marlin with support for firmware retraction in hopes that the firmware-retract command can ignore the configured extruder feedrate limit to still do rapid retract/restore, but I don't want to waste a lot of time on it if that doesn't work. Can anyone with experience with this feature confirm whether it ignores the normal extruder feedrate limit? Or, if you have experience with a similar configuration, can you share results on how well it worked?

Sadly this does not work at present. Setting an M203 E3 resulted in 6 mm retractions via G10 taking 2 seconds each vs the fraction of a second they're supposed to take.
Since it seems desirable for this to work, I've filed a Marlin issue to see if it's intentional or something that can be fixed.
In principle, G10 firmware retractions still make it easier to script a soluton (replacing each G10 or G11 by a sequence of M203, G10/G11, M203 to set E-axis speed then reset it around the operation) but this is less friendly to direct usage of same sliced files with different extrusion speed limits.

As a follow-up, I've been on Klipper instead of Marlin for roughly a year now, and it's easy to patch Klipper to have an extrusion rate limit for print moves only (not for retraction). So I have this working entirely with Klipper.


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Issue with 3D printer making super thin layers
Recently I've been having trouble printing properly on my Creality Ender-3 printer. I ran a pretty long print (approx. 15 hours) that turned out really well. I then started printing an attachment for the original print and saw that it was printing layers that were extremely thin.
I first scraped off the excess filament left on the extruder nozzle. Then, I heated up the bed and rubbed off the layer with alcohol. I tried printing it again but it still didn't print right.
Thin layer

Weird thing

From the images above, you can tell it's noticeably hard to see the layer, which shows just how thin it is.
I sliced the model in Ultimaker Cura. I set the layer height to 0.15 mm. I've printed models before with this height but the layer wasn't transparent.
What should I do to fix this issue?

Check your bed height. The bed is probably too close to the nozzle.

Wait, what? Can you give me a quick walkthrough on how?

There should be a good canonical question/answer on bed leveling but I don't know how to find it easily. Stick around and see if someone else can.

2 Things: first of all you want to level your bed to about a paper thickness from the nozzle in "0" position. Then, check your first layer thickness. I have set mine to always be 0.2 mm, which does aleviate problems with slight inconsistencies in the bed (like slight bends or kinks)

You need to level you bed.  Thin prints happen when the extruder is too low and is printing too close to the bed.

Download the following test codes from this address:
https://www.chepclub.com/bed-level.html
1) The first code is the most important you will want to run moves the extruder to five points on your board - Front Left and Right, Back Left and Right, and Center.  Using a folded piece of paper - I use a business card - drag the paper under extruder of each of the four corners.  You want to make sure you get a bit of drag when pulling out the paper/card.  If you feel have enough of a gap that you can run put the paper/card under the extruder and that you feel a bit of tug when pulling it out.  It runs the middle last - if you are having issue with the drag, adjust all four corners slowly until it is right.
2) The second runs the extruder in a square pattern on your board.  You simply want to run your finger of the print - if it sticks to the bed, you are good - if it doesn't, adjust your corners up and keep testing.

If your first layer is more thin than you expect it to be, the bed is too close to the nozzle. Note that you need to check the level an bed-to-nozzle distance once every few prints. Also, the first layer shouldn't be a too thin layer, the Cura default for a 0.4 mm nozzle is about 0.28 mm. Personally, I always use 0.2 mm.
The best solution is to re-slice the model with a thicker first layer. Next, re-level the bed to the proper distance of an A4/US Letter printing paper. You should feel some drag when you pull it between nozzle and bed.
Other solutions that also work include the redefinition of the Z=0 level, but this is not advised. Please fix the hardware.

authors: Юрій Москальов


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Ender 3Pro Calibration problem
I have a new Ender 3 Pro.  I set it up and everything seems to work. I configured as such that the nozzle is only a sheet of paper apart from the bed. When I go to print, the extruder raises 2-3 mm and starts printing, which doesn't stick to the bed and all I get is a mess. Bed is set to 60 °C and hotend to 210 °C.

mind showing a photo and telling us what slicer you use?

Hi Howard, welcome to 3DPrinting.SE! What is your start G-code? Or, put a link to PasteBin to your G-code file so we can help you. Unfortunately, your question does not have enough information to help you now. My best guess is that your start G-code is incorrect.

authors: موسسة مصادر المعمار


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Bottom Layer Compression (over extrusion) - Can't get rid of it
I've been trying to find a solution to a problem I've been having recently whereby the bottom layers of my print (1.2 mm; 12 layers) are either being compressed. over extruded or both. The problem results in the nozzle being dragged through previously extruded filament leaving deep groove marks and the bottom layers being risen/wavy, thus causing (I believe) the print layers to expand horizontally outwards
Settings are:

Anycubic Chiron
0.1 mm layer height
200 °C hotends temperature
55 °C bed temperature
40 mm/s print speed
eSun black 1.75 mm PLA
Cura 4.4.1

It's less noticeable on less intrinsic prints but for my latest project, its becoming a real issue. The problem is that for the square holes for the buttons (of which there are a lot), the bottom layers are extruding (essentially elephants foot-ing) which is impacting the tolerances of the build (holes should be 13 mm to accept 12.5 mm square buttons but are coming out at ~12.7 mm only on the bottom layer, I've measured the walls of the square holes and they're coming out perfectly).
I've tried almost everything I can think of/find on Google:

Levelling the bed (multiple times)
Tried print temps from 190 °C to 210 °C (even printed a temp tower which confirmed printing at ~200 °C is correct for my filament (eSun black PLA)
Calibrated the extruder
Calibrated the Z-axis
Set different horizontal expansion settings in Cura
Reduced entire print flow rates (have tried 90 %, 85 % and 80 %); this somewhat worked but produced problems elsewhere in the print due to lack of material (skin overlap etc.)
Used the 'modify settings for overlap' mesh setting to reduce infill flow & inner wall flow to 45 % and 55 % respectively for the bottom layers (up to 1.2 mm).

The last point in that list is where I've had the most success but it does leave a slight indentation around the outer wall until the full flow rate kicks in (i.e. >1.2 mm) and I'm thinking there may be other things at play that are causing the issue and I shouldn't have to do this reduce bottom layer flow so much if at all.
Has anyone seen this before?

Have you been able to confirm with a caliper that the 12 layers are actually 1.2 mm high? Maybe you have a mechanical problem with Z axis.

I haven’t done that yet but I printed and measured another test cube after calibrating the z axis and it was perfect (or near enough); 20.04

So I managed to figure it out and it turns out the vertical guide screws had a lot of grease/oil build up near the bottom which was impeding the X axis motor from properly moving the nozzle vertically when instructed.
After removing both guide rods and cleaning with degreasing fluid, the troublesome problem is no more!

I had the same problem with bottom 8-10 layers being squashed. Tried all the possible settings and nothing helped.
Eventually found that the bottom part of the Z-axis guide rails was narrower then the top and it was not rolling properly down the bottom.
Found out by taking off the Z-axis rod and moved extruder up and down and I felt it was moving a lot worse/getting almost stuck down the bottom. Also tried it by disabling steppers and rolled the Z-axis motor by finger, almost no effort at the top to roll it down, but took a lot more effort down the bottom 5 cm or so.
I loosened the screws and pulled the bottom part wider and problem solved... Probably a rookie mistake as it is my first printer....
Hope it helps someone saving days of experimenting.

Not sure which printer you have, but I have the Ender 3 pro and one of the first recommended mods was to make a spacer to sit between the z-axis motor and the frame because it is often at an incorrect angle as you describe. Adding that spacer makes the whole thing run much more consistently

The first thing that comes to mind is that, even though you have levelled the bed, the print nozzle may be too close causing too much "squish" on the first layer. Squish isn't bad as it promotes adhesion, but in your case, as you are looking for finer tolerances on the holes, it may be a problem. I use a feeler gauge and aim for 0.15 mm gap when printing at 0.2 mm layer height.
Next thing to consider is ensuring you have calibrated your flow rate/extrusion multiplier. See here for detailed procedure
Assuming flow rate is calibrated I can think of some settings in Cura that could affect your print.

Initial Layer Flow
Flow Rate Compensation Factor
Combing Mode / Avoid Printed Parts

Initial Layer Flow enable the use of a higher/lower flow rate in you first layer. Typically I set this to a value larger that my flow rate, 120 %, as I want good adhesion and am less worried about the elephant's foot effect. However, you could reduce it to less than your flow rate although that may compromise adhesion unless you use a brim.
Flow Rate Compensation Factor For most circumstances this should be 100 % which indicates that your flow rate should be used as set and not compensated for. I would check that this value has not been altered cause over-extrusion.
Lastly, there are two travel settings. Combing Mode and Avoid Printed Parts work in combination to reducing the impact of travels in the finished print. I would ensure you have combing turned on (e.g. Not in Skin) and that you have enabled Avoid Printed Parts. More details on these settings can be found here

I had similar issues during the past few days. My first 3~5 layers overlapped. I ended up with figuring out it was the screws to mount Z stepper became loose and the stepper shifted itself downwards instead shifting up the nozzle for the first several layers, until the stepper had nowhere to go.

I have had a similar problem after years of clean printing and spent ages messing with it until I read this article and cleaned my lead screws on the Z-axis - a quick hit with a brush seems to have fixed it - fingers crossed.
Problem: my layers looked over extruded in random areas inside models and by the time I hit the top layer, I got some pretty serious results with blobs big enough to change the detail and fill in large gaps with ooze.
I tried the following:

Tweaked my Cura settings for ages in case I had retraction set wrong, wiped back to factory defaults, regressed to earlier versions of Cura - no luck,
Replaced my hot end assembly pretty much three times over, no luck except to clog a few brand new hot ends lol
Used different filaments, dried filaments including new ones in the oven for a day, no luck. Probably wasted a couple of rolls of PLA persisting with trying to get a job completed through the problem.
Cleaned the lead screw.  It may have improved it somewhat but is difficult to tell as it is somewhat random.

UPDATE: The problem is not fixed, unfortunately.  I will try a more detailed clean of the lead screws tomorrow, but I ran a 100 mm clean Z-axis raising test and noted it was pretty close to the mark, but interestingly it was about 99 mm on the left side and 101 mm on the right, although I doubt this could fully account for the problem I am having from about 2 mm up the axis unless the z height loss occurs in one concentrated section right near the bottom. The printer previously printed well and has not been damaged in any physical way that I am aware of.  I will consider if there is any degradation in the functionality of the stepper motor by swapping them if more cleanup doesn't help.   Keen for any other ideas if you have any.

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.


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How to unload filament as cleanly as possible using the extruder motor?
I usually unload filament using the extruder motor, with the nozzle around 30 °C below the filament's print temperature. Despite this, often a significant amount of filament is left in the nozzle, and the filament comes out with a long stringy tip.

Does this suggest that the procedure might be leaving deposits of melted filament outside of the melt zone (potentially leading to blockages)? and if so,
What sequence of temperature/movement controls would be most likely to remove or mitigate the risk of deposits?

I am familiar with the “cold pull” technique, but I am looking for the best strategy for a solution using the printer's controls.
I usually extrude a quantity of cleaning filament when changing filaments, though I'm not sure whether this would also clean any deposits outside the melt zone.
I have seen a procedure called “cooling moves” in the Prusa Slicer code. I understand this is intended to produce a cleaner filament tip upon unloading in a multi-material scenario, and I wonder whether a similar strategy should be employed for regular unloading, although I am unable to tell from the code what exactly is happening.
I am using a genuine E3D V6 hotend and a Bondtech BMG Extruder.

Why do you reduce the temperature to remove the filament? I've always removed filament at printing temps with no problems. I get a small bulb and a thin string which represents usually the nozzle material.

I don't know if what I do is the best (or correct) way to do it, but I always just heat the nozzle up to the right temperature. Then, I extrude some filament and quickly pull the filament out. I have not had any problems with this technique at all.

@RosalieW By hand or using the extruder stepper? The OP is seeking for a non-manual solution.

I do it by hand. But, using the extruder stepper would for sure also work. You just have to make sure you pull out the filament quick enough. Otherwise, some filament might stay stuck in the nozzle and cause problems later on.

There's a bit of a compromise here:
Filament cohesion in the nozzle isn't strong enough to remove all residue at higher temperature
Extruder motors can't get sufficient grip / don't have sufficient torque for filament extraction at lower temperatures
That means you'll always have to purge some of the old filament when changing to a new filament.
To easily remove the old filament, you'd want to fill the nozzle, so that there's no large plug of filament that might get stuck in the Bowden tube (as suggested in a comment by Rosalie W), then pull the old filament out; and then purge the nozzle after inserting the new filament.
How much you'll need to purge depends a bit on the filament and its color, but I'd guess 50 mm should be sufficient in most cases.
As G-code, this might look something like that:
;Unloading
G91 ;relative movement
G1 E5 F300 ;fill nozzle
G1 E-300 F3000 ;unload filament, 300 = Bowden length + hotend length
G90 ;absolute movement

;Loading
G91 ;relative movement
G1 E295 F3000 ;load filament
G1 E55 F200 ; purge filament
G90 ;absolute movement


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Per-Model Bed Adhesion in Simplify3D
I'm looking for a way to have different bed adhesion for different models in the same print. My question is similar to this question, but I'm using Simplify3D.
I have an STL file that contains many different parts, and most of it prints fine except for a few small pieces which end up not sticking to the bed. I'd like to add bed adhesion for just the small parts while leaving the rest of the parts alone.
I started by splitting the STL file into smaller pieces with "Separate Connected Surfaces" then proceeded to make two separate print profiles, the first one for the majority of the parts with "Use Skirt/Brim" set to defaults (Skirt Layers 2, Skirt Offset from Part 4.00 mm, Skirt Outlines 2) and the second one for just the small parts with "Use Skirt/Brim" set to create adhesion (Skirt Layers 2, Skirt Offset from Part 0.00 mm, and Skirt Outlines 10).
I've then set the two processes to use their respective parts. When I go to print just the small parts alone I'm able to see the bed adhesion:

But if I attempt to print with all of the parts in the same print, the bed adhesion seems to drop down from 10 outlines to just 2 outlines but is still hugging the smaller parts. So it's like it took part of the settings ("Skirt Outlines") from one process and another part of the settings ("Skirt Offset from Part") from the other process to generate the final print.

What I'm looking for is how to have separate build adhesion for separate parts in the same print.


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Can this part be 3D printed?
I have an old air conditioner and most of the vent flaps/louvres are missing. I've modelled it in Solidworks, but can it be printed? Are the tips too small for 3D printers? It's about 14 cm long end-to-end.

Here's the drawing sheet (dimensions are in mm):

What 3d printer do you have? What is the smallest sizes? What filament are you using?

@marcellothearcane I'll be taking it in my local library and they've got a UPBox using ABS. I've just added the drawing sheet in the OP.

Hi @JohnM.  Almost anything can be printed with enough support material.  Are you asking for a design review and an analysis of the best printing plan?  It really isn't possible to answer this question in a way that would be helpful without more information about your goals and constraints.

Dimension-wise it's probably ok.
If you want to print it as a single piece it would be quite challenging because of the cylinders, overhangs and bridges present in multiple directions: overhangs and bridges result in lower quality and precision, while cylinders can be printed nicely only when their axis is vertical.
However I see that you could easily split the component into multiple parts, each one of which could be printed optimally.
You can glue the different parts together and you are done, see What glues for PLA? and What glues to use for PETG?

This could be printed with minimal supports if printed standing slightly canted by around 30° on the right side in the picture.

Interesting. I'll split the part into 3. I suppose the cylinders should face up when printing?

Into 3 parts? Why not split it in half then you get 2 half Louvre doors of about 2.5 mm thick which you can glue together. ABS might be challenging to print it upright or slanted under 30 degrees. PLA/PETG is less prone to warping, I would prefer that over ABS.

Printing in two parts seems a good solution to me

Printing it cut in 2 parts upright also allows to directly access the internal area through the "center" cut, and insert a stiffening piece of metal along the whole length.


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How much plastic pellets does it take to make 1 kg of filament? (making my own 3D filaments)
Maybe this is a stupid question, but is 1 kg of plastic pellets equivalent to 1 kg of filament? I want to extrude my own filament using recycled plastic pellets. I want to know the cost of my material in general, so I was wondering if 1 kg of plastic pellets result in 1 kg of filament (regular spool)? How much plastic pellets are needed get 1 kg of filament?

Hi @Deborah, and welcome to the 3D printing group.  Questions may be on-topic or off-topic, but they are never "stupid" when asked with good intention.

As Fred.u said - if the extruder has a large reservoir, you may lose that much material once in each run.  E.g. if the reservoir uses 10 g, then you lose 10 g no matter whether creating  100 g or  10 kg of filament in a single run.

If you ignore losses due to production machinery, your one kilogram of pellets will provide you with nearly one kilogram of filament. There may be some small loss of material stuck in the auger and drips from the nozzle and any place you discover plastic that is not on the spool.
How many plastic pellets does it take to make one kilogram of filament? One kilogram plus a bit more. If you are asking about the numerical quantity of pellets, how much does one pellet weigh? Are they large pellets or small pellets?


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In OctoPrint when receiving temperature data (M105) what is T0?
I've setup OctoPrint with the goal to log temperature data of my hot end. So, I've enable serial logging and examined the serial log file.
The Output for an example line is as follows:

Send: M105
Recv: ok T:20.7 /50.0 B:20.0 /0.0 T0:20.7 /0.0 @:0 B@:0

So, from what I understand:
T = Thermistor temp of hot end °C
In the example, current temp is 20.7 and target temp is 50.0
B = temp of bed °C
In the example, current temp is 20.0 and target temp is 0.0
But what is T0?
Or the @ and B@?

T is the selected tool, T0 is the first hotend tool. If you only have one hotend, T and T0 are exactly the same.
Do note that G-codes are described on the G-code wiki page, for M105 you can find:

The parameters mean the following:
   - T, T0, ..., Tn - extruder temperature. In a single extruder setup, only T will be reported. Some firmware variants will report no T0 in multi extruder setups - in that case T is to be considered the temperature of the first tool. Otherwise, T should be considered the temperature of the currently selected tool (which will be repeated in one of the Tn entries)
   - B - bed temperature
   - C - chamber temperature
   - @ - Hotend power (Prusa only)
   - B@ - Bed power (Prusa only)
   - P - PINDAv2 actual (Prusa MK2.5/s MK3/s only)
   - A - Ambient actual (Prusa MK3/s only)


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Finding the right material to print RC CAR cover
My problem is that I have used a 3D printing machine from the University and found out that the cover for the car was not smooth even after using sanding paper and painting it.
What material would work best to print  the cover of the Cyber truck. I want it to be light and smooth.
I have to print it from any online companies that have this service here in Germany.

welcome to 3DP/SE.  "Smooth" is not necessarily helpful as an adjective here, as it means different things to different people in different contexts and applications.  Perhaps photographs would help to highlight the specific problems you are facing?  Also, I am confused by the question a bit, since the first part makes it seem that you have direct access to a 3D printer, but the second part suggests that you are purchasing services.  There may be different answers for the two situations.

@cmm, I do have access to printers, however from previous experience I was not happy how the covers of the rc cars looked like and that is the reason why maybe an online service with a different material would be better. I have used PLA

I have 3D printed models which were then sanded using progressively finer grades of sandpaper, terminating with wet sanding using micromesh to 12000 grit. The result was smooth and shining without any coating applied.
If your original results were not acceptable, the process may have been flawed and should be re-considered for technique.
For your purposes, as a body for a radio controlled vehicle, you'll want to consider something that can manage an impact reasonably well. ABS is going to be less expensive and provide some energy absorption but will have layer lines that require sanding and finishing. Layer thickness plays a substantial part in providing for good results and a smooth finish. I used 0.100 mm layers to get optimum smoothness.
You could request your model to be created in nylon using the SLS method, but the surface will be granular and would also require sanding to accomplish a smooth finish.
SLA or MSLA resin printed models will provide a very smooth surface, but the material is brittle and may crack during "on-road" use. You may find a printing service which offers to create using a more flexible resin, but you'd have to request that or confirm the selection when placing the order.

Don't forget ABS can be vapor smoothed with acetone :-)

I've done a number of ABS models and the vapor smoothing works great. It's not so good for details, but on a full-scale banana, the results were striking!

An RC car hood could be 3D printed, vapor smoothed and then the edges re-crisped with sanding. Also, note that ABS is often said to sand neater.

ABS requires a printer with enclosure, or it will warp and never match very accurately the shape of the cover you expect.

@FarO, It's not an absolute that ABS requires an enclosed printer. I've printed ABS on a genuine Prusa MK2s and a Robo3D R1+ with no distortion. Using a full height ooze shield will often resolve any cooling problems.

Choice of Material
PLA is an obvious choice, but it has drawbacks compared with ABS.

PLA is more brittle than ABS.
PLA softens at a lower temperature than ABS.
PLA is not treatable with acetone for vapor smoothing.
PLA can not be glued
    with (most) solvent-based adhesives.

I would consider ABS or ASA to be good choices for an RC-car body.
Getting Smooth Surfaces
To get a really smooth surface, after printing with thin layers and good print settings to minimize strings and blobs, you will want to treat the surface.  The two most common techniques are sanding and vapor smoothing.
Wet Sanding is Great.  Dry Sanding is Not.
Sanding is a great smoothing technique for PLA and even for ABS, but one must be careful.  In addition to some of the sand paper grains being aligned as proper cutters to remove material, many grains are uselessly aligned and simply contribute to friction.  The plastics used in FFF printing are, by definition, thermoplastics and will melt.  One can easily soften and even melt plastic with dry sanding.
When the plastic softens, it can form little balls which dig into the surface, or stick to the surface.  These hurt the surface finish like snowmen mar a field of freshly fallen snow.
Any sanding should be done wet, with wet-rated paper.  Work up through the grits.  Lower grit abrasive removes more material so that the surface can be "even".  Lower grit lets you sand out the layer lines quickly.
Use a Sequence of Grits
Higher grit papers remove the scratch marks of the previous grit.
Generally, I go up by about 50% of grit number at each change.
When I am removing a lot of plastic and want to end with a glossy surface, I go through this sequence:  36->80->120->180->220->330->400->500->1000->1500->2500->3600->5000.  Yes, I know that there are some big jumps there, but I haven't happened to stock papers at intermediate points, and it works for me.  Depending on how smooth the surface already is, or how much material I must remove, I start further up the progressing.  For 3D printed objects, I start at 220.  The last three are critical.
Consider Adding Vapor Finishing to you Toolbox
Vapor finishing of ABS can give some very fine and glossy results.  It is worth trying, although be aware that acetone mist is very flammable.  If you are heating the acetone, treat it as life-threatening and possibly explosive.
If you use vapor finishing, consider that the acetone goes into the ABS.  A warm soak or vacuum degassing could help remove it.  You don't want the hood of your RC car to start bubbling in the sun as the acetone is motivated to escape.

You may consider PETG too. It's not as strong as ASA or ABS but it's much easier to print.
You can polish it by first sanding and then flame-smoothing.
See this video from CNC kitchen about comparing the different materials (ABS is not considered because similar to ASA in properties but more difficult to print) and see this video about flame-smoothing PETG.


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Any experience with nylon drying on heated build platform and printing on paper?
A while a go I thought that I could try printing in Nylon on my Wanhao Duplicator i3 with full metal hotend. Boy, was I wrong: The filament was not dry and popped like foam. The platform (Buildtak) was not sticking at all (at any temperature), I had the cooling fan at 100 %, so the bits that stuck to the platform warped like the Enterprise.
I learned that a filament dryer, an enclosure, Gaolite and PVA glue will be my friends, but I am determined to not spend a lot of money to printing something that I don't need often. (PLA works fine for me)
I am now at the point that I dry my filament by leaving a roll of nylon on the heated buildplatform at 90 °C. It stopped popping and hissing, so I guess that works. I learned that nylon sticks to cellulose, so without needing to recalibrate I can tape a piece of printer paper to the build platform and it sticks like crazy! Extra bonus is that if it warps, the paper curls up slightly and keeps the print from falling off. I have only printed a single test piece until now, so I can't really say if it's to be recommended.
Has anybody used these methods (drying nylon on heated build surface and printing nylon on paper) too and have you found any downsides?
To make this a worthy stackoverflow question: "Can I dry nylon on my heated build platform and print nylon on paper?"

This question would probably be a better fit for this site if you factored it as a "how to...?" question part followed by a self-answer, and also considered other answers before accepting your own.

The two topics (drying and adhesion) are quite different. They belong to different questions.

Heating spools on the bed can be an option, but it seems inefficient to me: you lose a lot of heat and an oven would save quite some energy. Also, I wonder whether the open air will reduce the effectiveness even more, since the outer parts and the top of the spool will be colder.

also, the bed would heat it unevenly, while the oven evens out the temperature better


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Big cracks on the Layer view in the Preview mode of Cura
I designed a part on Fusion 360 that looks like this:

The part is very small, about 20 mm for 10 mm. I'm then importing it to Cura and I notice they are huge cracks on the part when simulating/previewing the print, I'm using a Monoprice mini printer, 100 % infill, and 0.0437 mm.:

This is my first-time 3D printing something, so maybe (most probably) I did something wrong.

@R..GitHubSTOPHELPINGICE I think is the resolution of the profile, please look at the top right corner of the last image

Consider upping the triangle (polygon) count by decreasing the mesh size  in the original item prior to exporting.  That kind of mess should not show up even in parts far smaller than this.

You have coasting turned on. Cura shows the coasting locations (where extrusion is switched off) as gaps. The actual print may be fine.

That's likely the case, but it's not ok. Coasting will seriously mess up your prints. It's a really dubious feature that's a poor substitute for other measures (correct retraction settings, and linear advance in firmware if you'll be mixing print speeds or have high speeds relative to acceleration limits).


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Print of fine hole seems to twist
My model is a keycap for mechanical keyboards. There is the cap itself, and a stem with a hole in the form of a cross, which fits the switches themselves.

I print in the same position as it is intended to be used, top up. This means that the stem and the cap are not connected until quite a few print layers.
To prevent the stem from falling off during the print (it has a small footprint), I created connectors in the first layers, to hold it in place.

The issue: it seems like all my prints have a rotation of the stem, compared to the cap. It probably rather is the cross-shaped hole, or its walls, that are not completely symmetrical. I do not think it is only the edges against the printing bed that are the cause, since I have trimmed them with a scalpel. The rotation is always in the same direction.
The twist is detectable when watching the keycap with the switch, and more so with keycaps on switches on a keyboard plate (you can see that the edges of the caps do not align. They do in my CAD program):

I use Cura as my slicer, layer height 0.06 mm, and ABS. I attempted a slow print (30 mm/s), which didn't help.
The first work-around that comes to mind is to measure the twist and compensate for that in my model. But I believe that since the problem is in the printing process, the problem would best be solved in the slicer.
What could possibly be the issue? Is there an option is Cura to compensate for this? Short of the work-around mentioned above, what are other steps I should look into?

This is a great first question.  Welcome to the 3D Printing Stack Exchange site.

This looks like a shift rather than a twist.
Looking closely at the "+" opening, it doesn't look as much twisted as it looks as if the top and bottom halves are sheared, with the top half shifted slightly right and the bottom shifted slightly left.  The horizontal part of the plus seems aligned on the left and right halves.
When you press-fit the keycaps, you will "average" the displacement forces and the keycap will twist.
I am suspicious of a backlash problem in the X axis (left to right).  Perhaps the belt isn't tight enough, or some part shifts differently.  It could be in the rails, the belt, a loose drive pulley, the hot end being slightly loose on the carriage, or any uncontrolled movement.  It could be a high-friction x-axis which causes spring wind-up in the drive system.
I recommend carefully examining the printer for any excess friction or movement, and taking action to fix that first before tweaking the model to compensate for what can not be fixed.
If it is a twist, use more cooling.
If the photos have misled me, and the vertical "+" shaft if actually twisting, you may need to use higher cooling.  The drag of the filament as the head traces the perimeter can create a torque on the shaft, and if the plastic is not sufficiently cooled it could be dragged around.  I consider this more of a theoretical problem than a real one, and have not yet seen it in practice.
This is a beautiful design
This is a wonderful application of 3D printing.  With a multi-material printer it would be tempting to label the keys similar to old-style multi-shot keycaps.

I think you're right everywhere here, it is a shift. I'll have to read on how to run a diagnostic on the printer. Could a torn print nozzle cause this? The small amount of extrude that occurs before the print starts often wiggles around and gets back to the nozzle and sticks to it (I detach it with a spatula every time), I don't know if this is a smoking gun.

Thanks for the appreciation! As for printing labels, I do want blank keycaps so it's not applicable for me. But the design is on github, if anyone wants to do anything with it. https://github.com/fleutot/dsa1u

Another possibility is that those connectors you put in are pulling the cross-pattern off-center.   Is there enough height that you could specify supports in that area instead?  If so I'd recommend a brim "everywhere" to help stabilize the supports under the centerpost.
If there is sufficient clearance in the mechanism itself, consider expanding the diameter of the post (not the cross itself) to increase stability as the print is in progress.

I'm not sure what you refer to with "that area". Increasing the connector height is worth a shot, but it's the hole that shifts, not the circular edge of the stem. Although it's hard to be sure.

I meant that presumably the center post doesn't reach down to the buildplate.  If it does, then yeah, supports are irrelevant.

I see! The center post is what first out of the nozzle, it's all the way down. There no support in the usual meaning, just connectors to stabilize the post until it merges into the cap.


text:
My first layer becomes solid when sections are supposed to have small separations
I've only been 3D printing for a few weeks and most of my prints seem to come out fine, but when I try to print models which require a small clearance between sections of the model, e.g. various tolerance/clearance tests and some others, I can't get them to separate when they should because the bottom layer is a solid plate with no gaps.
For most models, this seems a good feature as they stick well and the final surface is completely flat, but for some, I want parts to be separable, so there should be some clearance on the first layer..
From some research, I suspect it may be either that the nozzle is too close to the bed or that the bed (or nozzle?) temperature is too high.
I have an Ender-3 and use PLA with a 200 °C nozzle temp and 60 °C bed temp. When leveling, I've been using a post-it note to set the nozzle clearance. I've tried dropping the bed temp to 45 °C and even 30 °C, but this didn't change the first layer printing of the Maker's Muse tolerance test, which still came out with a completely solid first layer and hence was basically a brick! I also tried using a raft, but the result was that the raft couldn't be removed from the model so this changed nothing.
What should I try to improve this?

Some details:
I'm using CURA 4.4.1 with as far as I can tell mostly default settings. I've tried the profiles Standard Quailty 0.2 mm and Super Quality 0.12 mm but this doesn't change things. FYI, as you might guess, I haven't changed the default nozzle so it's 0.4 mm.
The main reason for the question is that I don't know where to start with adjusting the settings, so had hoped someone would ask for the value of specific settings rather, than a full lisy, since most of the seem to do with the structural integrity of the body and shell of the model rather than the base, but here goes...
Shell:
    Wall Thickness: 1.2 mm
    Wall Line Count: 3
    Top/Bottom Thickness: 0.8 mm
        Top Thickness: 0.8 mm
        Top Layers: 4
        Bottom Thickness: 0.8 mm
        Bottom Layers: 4
    Horizontal Expansion: 0 mm

Infill:
    Infill Density: 20 %
    Infill Pattern: Cubic

Material:
    Printing Temperature: 200 °C
    Build Plate Temperature: 60 °C
    Flow: 100 %
        Wall Flow: 100 %
        Outer Wall Flow: 100 %
        Inner Wall Flow: 100 %
        Top/Bottom Flow: 100 %
        Infill Flow: 100 %
        Skirt/Brim Flow: 100 %
        Prime Tower Flow: 100 %
        Initial Layer Flow: 100%
    Enable Retraction: [Yes]

Speed:
    Print Speed: 50 mm/s
    Travel Speed: 150 mm/s
    Initial Layer Speed: 20 mm/s
    Initial Layer Print Speed: 20 mm/s
    Initial Layer Travel Speed: 100 mm/s

Travel:
    Avoid Printed Parts When Traveling: [Yes]
    Avoid Supports When Traveling: [On]
    Travel Avoid Distance: 0.625 mm
    Z Hop When Retracted: [No]

Cooling:
    Enable Print Cooling: [Yes]
    Fan Speed: 100%

Support:
    Generate Support: [No]

Build Plate Adhesion:
    Build Plate Adhesion Type: Skirt

Dual Extrusion:
(No settings - single nozzle)

Experimental:
    Tree Support: [No]

Printer Settings:
    X(Width): 235 mm
    Y(Depth): 235 mm
    Z(Height): 250 mm
    Build Plate shape: Rectangular
    Origin at Center: [No]
    Heated Bed: [Yes]
    Heated Build Volume: [No]
    G-Code flavor: Marlin

Printhead Settings:
    X min: -25 mm
    Y min: -32 mm
    X max: 32 mm
    Y max: 34 mm
    Gantry Height: 25 mm
    Number of Extruders: 1

Start G-code:

    M201 X500.00 Y500.00 Z100.00 E5000.00 ;Setup machine max acceleration
    M203 X500.00 Y500.00 Z10.00 E50.00 ;Setup machine max feedrate
    M204 P500.00 R1000.00 T500.00 ;Setup Print/Retract/Travel acceleration
    M205 X8.00 Y8.00 Z0.40 E5.00 ;Setup Jerk
    M220 S100 ;Reset Feedrate
    M221 S100 ;Reset Flowrate

End G-code:

    G1 E-2 F2700 ;Retract a bit
    G1 E-2 Z0.2 F2400 ;Retract and raise Z
    G1 X5 Y5 F3000 ;Wipe out
    G1 Z10 ;Raise Z more
    G90 ;Absolute positionning

Material is Generic PLA:
    Default Printing Temperature: 200 °C
    Default Build Plate Temperature: 60 °C
    Retraction Distance: 6.5 mm
    Retraction Speed: 25 mm/s
    Standby Temperature: 175 °C
    Fan Speed: 100 %

Standard Quality Settings:
    Quality:
        Layer Height: 0.2 mm
        Initial Layer Height: 0.2 mm
    Shell:
        Wall Thickness: Calculated
        Top/Bottom Thickness: Calculated
    Support:
        Support interface Thickness: Calculated

Super Quality Settings:
    Quality:
        Layer Height: 0.12 mm
        Initial Layer Height: 0.2 mm
    Shell:
        Wall Thickness: Calculated
        Top/Bottom Thickness: Calculated
    Support:
        Support interface Thickness: Calculated

As you may already know, there are lots of other settings which, by default, are not visible. If you need the value of one of these, I'll turn it on and see what it is.
I've also got a few of the failed pieces out of my junk box and added a couple of photos/ As you can see, the underside is beautifully flat and solid.

I also tried this test, but the only reason I got one of the pegs out was it broke off the base layer!

Update2:
Results of trying to increase spacing when levelling.

Update3:
Not an answer to the original issue, but I found a workaround in that there is an option in CURA to turn off the "drop model to build plate" option, so the whole model can be made on supports. This then doesn't have a 'solid' first layer and I get a test piece which shows I can print down to a separation of 0.2mm and have the parts remain free; 0.15 doesn't free up.

Original attempt, new version and the support.

PostIts are listed as 30-thousands of an inch, so 76.2 µm, about 3/4 of the 100 µm that we aim for.

What weight of paper is recommended? Most people just seem to say "a piece of paper". I have either 80 g/m² or 120 g/m², both A4.

Your settings show adhesion is set to skirt, but the first print looks like it was done with a brim or something...

@R..GitHubSTOP I HELPINGICE I mentioned in the question that I tried using a raft. The samples in the picture include that case.

If that's a raft, it looks like you broke/cut away the parts of the raft not under the print rather than separating the raft from the print. Was it bonded so that it couldn't be separated?

Exactly. The raft simply wouldn't separate as it was firmly bonded to the model. Attempting to pull it away simply broke sections of the raft.

By the way, the model with the raft actually had a 2nd model with it which is why it seems so wide.

The overall flow rate seems ok -- I see a nice gap in the 0.2 mm peg case.
The most likely problem is the first layer is too thin, or to much material is being over extruded.
I don't know Cura as a slicer. It may have an option to over-extrude the first layer. Unless I found such a parameter, I would look at how z=0 is set.
Just add an experiment, try using 3 Post-It notes. How, if at all, does the result change? Do you still have adequate bed adhesion?
If you can make the first layer thicker, it might be relatively closer to the actual thickness. Can you program a 0.35 mm first layer?
If you can't make the first layer thicker, maybe try setting all the layers to be thick. It might not handle the overhang as well, but today's question is about the first layer expansion

Last night I tried using a piece of 80 g/m²  A4 paper and setting the height so the "tension" felt when moving the paper with the nozzle at Z=0 was slightly less than I've been doing previously and, after watching the first couple of layers,  left the printer working on a couple of boxes overnight, as I've down over a dozen times before. This morning I came down to my first example of "spaghetti". Measuring the partial model that printed, it looks like part of the model detached from the bed around layers 8 or 9 out of 70. Obviously, I've gone too high and need to reduce!

uhm, spaghetti at layer 10 means something else is afoot probably...

Spaghetti is a good meal but a terrible print.  An 80 g/m^2 paper should not have been too thick.  Perhaps you have a bed adhesion problem that was masked by a high first-layer squish?

As I said, this is the first time I've either got spaghetti or model separation after the initial layer. I've usually stopped the print if either the skirt or the initial layer doesn't stick. So when I used a thicker piece of paper and allowed less "tension" against the nozzle at Z=0, I watched it produce the first and 2nd layers then assumed it would be OK.

At least I've identified a possible reason for the spaghetti ... The hot end cooling fan had stopped. Voltage on the board seems OK, so I assume it's the fan and have ordered a replacement. I've also had to replace the Bowden tube as the PLA had melted inside the tube, presumably because the heat sink got hot, and, when I tried to retract it, it got stuck partway up the tube.

You can clean out the tube of PLA by placing it is boiling water and then squeezing or rolling out the bump.


text:
Closed-loop stepper motors
I am thinking to use closed-loop stepper motors to prevent step loss and make the machine more accurate. What options (preferably low cost) are there for:
stepper motor + driver + encoder + microcontoller
Is building it from scratch worth it? E.g. Arduino Mega 2560 + RAMPS 1.4/1.5/1.6 + stepper motors (e.g. NEMA17) + drivers (e.g. A4988, DRV8825) + encoders (e.g. AS5047P, AS5047D, AS5048A, TLE5012B) + microcontrollers (e.g. STM32).

The RAMPS setup is completely outdated anyway.
BTT offers a complete setup for closed loop steppers: https://de.aliexpress.com/i/33000419800.html
However, I think the benefits lie more with CNCs. If you lose steps - even if they're corrected soon after - you'll still have artifacts in the print from the other axes that kept moving.
Just use drivers that make losing steps a lot less likely in the first place, e.g. TMC5160s, and make sure you mechanics work well.

A number of options exist, but keep in mind that cost will be a limiting factor.
(Small sidenote: cost depends on persective, financial cost does not equal mental cost. The tradeoff between buy or make depends also on your willingness to persist when things don't work right away.)
Before you start: make sure that your printer has enough space to accomodate bigger motors.
So, what options are there?

Change your current configuration. If you are losing steps, it could very well be that it can be fixed in firmware.

Pro: No budget and nothing to lose.
Con: No shiny closed loop system. (Is that bad though?) Possibly need to configure and compile your own firmware.

MacGyver / DIY solution based on low lever components

Pro: Probably as cheap as you'll get depending on how you choose your components. Might be an interesting learning experience, not to mention the satisfaction afterwards. This could be the smallest build size you'll see in all the options.
Con: You'll need a decent amount of engineering and debugging. Might be tricky to mount the encoders.

Same as 1, but now consider using of the shelf stepper motors with integrated encoders.

Pro: Most robust option on a budget in my opinion due to the single mechanical piece (motor + encoder).
Con: Integrated encoders have a considerable cost and are large compared to their vanila versions.

Go for off the shelf motor+encoder and drivers.

Pro: No need to worry about driver configurations too much. Just plug in the numbers or set the dip switches. Very conveinient solution. Pretty much plug and play.
Con: This will already be challenging on a budget. Making a wrong mix and match might lead to unpredictable results such as drives going in overcurrent. (Which, believe me, is very frustrating for your application!)

If we are allowed to consider servo motors: ClearPath-SD series (Or any alternative for that matter!) I'm just including this for completeness.

Pro: Performance wise a clear winner on pretty much any relevant level.
Con: You'll need a big budget!

Bottomline: You'll probably want to give the first option a go before spending money. Next stop, you might want to take the second option (you already did research on different specific low level components), and if you have time to spare I'd go with that as well. If you are also on a budget timewise, I'd definively suggest to take the third option with existing driver boards.
The other options are more cost heavy and become real options in produciton environments, where downtime is also costsing money.
As to the microcontroller, take whatever you have available. Just know that more computational power will allow you to output steps faster and will allow for smoother movements. Lot's to talk about there as well!

So, I am one of those who has implemented this on my big scale heavily modified cr-10 S5.
Why?
Well with bigger prints, the risk of crashing into itself because of a small blob is very real. Possibly ruining a 100$ worth of filament and missing deadlines. (We are using this professionally.) Blobs will happen, especially if you run low cost filaments and PETG, which is the only sane option for functional bigger prints from a cost perspective. We are using the BTT system S42B on all axis and it works well. A blob is now just a small distraction which can be polished away but the remaining print is still dimensionally correct.
However, it is not a trivial task to actually implement. To make this work one needs a printer main board allowing for external stepper drivers, like SKR E3 DIP,SKR V1.4,SKR V1.4 Turbo and so on. Also there one needs to tune the PID:s for the system in use which is not super simple.
If you are truly an expert and do big prints, I really think this is a must have upgrade. On the other hand if one are only printing smaller parts on a hobby scale this will not be a worth while upgrade. I am not talking about the money involved, the pcbs are just 14$/pcs but the work needed with new cabling pid-tuning marlin-digging and so on. For us it is just amazing to not have 30% failures any more, du to the inevitable blobs sometimes appearing in bigger prints.

I don't see the relevance for the question asked

100 $filament was about 4 to 5 kilos of normal priced PLA or ABS in 2020.

I've implemented a closed-loop system about 25 years ago on an 8 x 32 erosion table scanning it at one cm resolution using laser triangulation. It took 120 hours to scan the surface. Most of the time was spent waiting seven seconds for the system to stop shaking. I put shaft encoders on the X, Y, & Z shafts, not the stepper motors. I wanted to sure I got the movement of the camera.
In the end, I settled on moving to a goal with a 1/10 mm tolerance and added any error into the move to the next goal. There was a sphere of confusion of the location of the camera of more than 2/10 mm. Moving back and forth to make up for a missed step at the cost of nearly 10 seconds a move could add days to a run. We were well past the end of the table's life.

It doesn't look like an answer to the question asked

It has been 25 or 30 years since I did my first closed-loop system. I was driving a syringe pump from a printer port on a MS-Dos PC that ran hot had to disable the timer interrupts to make the deadlines amount moving the plunger, updating the floppy drive reading and computing the new position, getting the time, and fixing up the timer.
I found moving to a goal with a tolerance of 1 or 2 stepper motor steps was on the money over 95% of the time and I made deadlines over 90% of the time. Any error was made up in the next move. I used the same scheme on an 8 x 32 foot structured light scanning table.  I am pretty sure I saw memory errors from cosmic rays on this one. It took 500 hours to scan that with no parity check on the RAM. It had some wooden structures that changed size over time. I could track the movement with the error files from the shaft encoders.
On the x y scanning table, the wait time was7 seconds after a move before the camera stopped asking enough to capture an image. We elected to fix up the position in software and accumulate the errors in the next move in order to be able to finish the project.

Hello Gordon, welcome to 3DPrinting.SE! Although the answer is quite extensive, how does it help the OP in the decission to build from scratch is worth it or not. Could you please explain this with reference to your example by an [edit]? Thanks!


text:
Is there a spiral lid mechanism
I want to put a spiral lid on top of a container. When the lid opens, then the spiral mechanism will rotate into the container. Is there a name for this mechanism? If not, would something like this be possible?

Please post a drawing of what you are thinking of.  If  Iris diaphragm or "venus box" suffices, that's great, but if you'd like something more complicated we need to see it.

It sounds like you're talking about an iris diaphragm. This has many parts that slide against each other, and would best be printed as separate parts, then assembled.

Thingiverse also has examples of both the iris mechanism and the venus box.

No spiral lids that I know of. I'm not sure how they would work, anyway. There are plenty of designs with hemispherical lids -- so-called "Venus" boxes. Check Yeggi:
Yeggi : Venus box


text:
Does the Elegoo Mars printer support additional file formats?
I recently bought an Elegoo Mars 3D printer.  Generally speaking, I'm quite happy with it. But, I don't care for the slicing software, Chitubox.  Does the Elegoo Mars support other 3D file formats?  I have tried *.stl files, but they don't seem to work with the factory firmware.

Stl files are source models, not the sliced data for the printer. I'm not familiar with resin printer file formats. What does their proprietary slicer output?

A Chitubox file, with a *.cbddlp extension.

Searching for it turns up that it's the same thing as .photon format and there are a number of open source tools for working with it. I would start with googling "photon slicer" and see what you find in the results.

It also works with the .photon format of the Photon slicer.
It is only marginally better than ChituBox though.


text:
How can I solve the problem of line distortions on my prints?
Hello guys I have a little problem with printing. Whenever I print something there are always these lines my printer does, it's not a very big deal, but it looks rather ugly and I'd really appreciate it if anyone could help me if you know what the problem is. I post also a picture to show you the problem clearer. From what I see (observing how my printer prints), I noticed that it starts printing at one point and then when it arrives again after a circle to the starting point to print the layer above, it stops just a millisecond (instead of keep moving smoothly) and I think that's how the problem is created. I'm pretty sure its not the printer's problem, but probably the G-code or the filament... I don't know for sure.
Here some details:

Printer: Creality Ender 3 Pro
Slicer: Cura
Filament: PM filament, PLA, 1 kg, 1.75 mm

That's a pretty common (and unfortunately somewhat normal) problem - called "Z seam"

Have you seen any improvement when using "random" for layer change positioning?

@Davo: In my experience, "random" just makes warts all over the place rather than all in one place where you could sand them off.

@R..GitHubSTOPHELPINGICE then I suggest your advance/retract settings are not high enough.

@Davo: I mean without fixing the fundamental cause of the warts. If you get rid of them and there's only a very subtle seam left then yes random might look better.

As towe noted in a comment, that's Z seam. The mechanism by which it happens is mostly the same as bulging corners. The print head is moving considerably slower just before and just after the layer change, decelerating to a stop then accelerating back up to speed in order to perform the slow Z-axis move, but the rate of extrusion, which is dependent on pressure built up (in the compression of the filament, and possibly expansion of the bowden tube) between the extruder gear and the nozzle, not directly on the motion of the extruder gear, remains the same.
In my opinion, the best fix for this is upgrading to firmware that compensates for it. In Marlin firmware (the stock Ender 3 firmware is based on Marlin 1.0), this feature is called Linear Advance. You tune a spring constant for your material's compression, and after setting it, extrusion is roughly proportional (linear) with respect to logical E-axis moves, regardless of the speed the print head is moving. However, upgrading firmware is nontrivial to do, and has a lot you might have to tune/tweak to get it working the way you want.
Short of that, there are a lot of ways of mitigating the problem:

Select "Outer Before Inner Walls" option (in Cura, or equivalent in other slicers) and "Infill Before Walls" when slicing. This will ensure the layer change happens inside the model (on an inner wall) not on the outside surface, because outer surface is neither the first nor last thing printed on the layer.
Increase X/Y acceleration and/or jerk limits so that motion can start/stop a lot quicker, so there's a shorter period for the disproportionate extrusion to happen in. But if you do this too much, you'll get layer shifts (failed prints) or at least bad vibrations that show up in print surface. My Ender 3 can handle accelerations up to at least 3000 mm/s² in X and Y and 10 mm/s "jerk" (a misnomer, thus the weird unit) and you can likely go higher if you experiment.
Tell slicer to retract at layer change. This will prevent extrusion from continuing during the Z move, but won't help with the extrusion during the time you're decelerating/accelerating in the XY plane.
Increase Z acceleration/jerk. This will reduce the time spent during the Z move, and might even allow the head to keep moving without coming to a full stop during layer change (but that can't happen if you turned on retract at layer change).
Print at lower speed. If the max speed is lower, it takes less time to decelerate/accelerate from/to it, and nozzle pressure will be lower (so extrusion is naturally closer to linear).
Enable coasting in your slicer. This is a hack that really poorly approximates what Linear Advance would do, but it can lead to underextruded walls and brittle prints. I always had bad luck with it and don't recommend it, but it's an option.

I would recommend starting with items 1 and 2. #1 is good for a lot of other things too, and the only tradeoff is that overhangs might print worse (in my experience that's not really the case and they sometimes print better even). And #2 will get you faster prints (sometimes at lot faster) which is nice.


text:
Can you cure resin with sunlight through a window?
If I set my prints on the window sill (indoors) will the sunlight still be able to cure the resin? The problem with setting them outside is the wind knocking them over.

I'm not writing this as an answer because I'm not sure and don't have experience with resin printing, but generally glass does not significantly block UV unless it has special coatings to do so. So it seems like it should work.

Most windows have UV filters on them, reducing the effectivity extremely.

I second the comment of @Trish; my glasses have a coating that turns them into sunglasses under UV light (needed for my sensitivity for light). But, this doesn't work in the car, house or at work. Windows block UV light.

The glass will block most of the uv light; but not all. It will depend on the type of light that the resin is sensitive to; in order to determine if it will continue to cure behind a glass window in direct sunlight. Some resins also sensitive to blue light. You will need to look at the material data sheet for the resin to be able to know for sure. Be advised though, that the resin does not stop curing, and will continue to cure slowly over time, just sitting on the desk.
https://www.thoughtco.com/does-glass-block-uv-light-608316
From the link:

Glass that is transparent to visible light absorbs nearly all UVB. This is the wavelength range that can cause a sunburn, so it's true you can't get a sunburn through glass. However, UVA is much closer to the visible spectrum than UVB. About 75% of UVA passes through ordinary glass. UVA leads to skin damage and genetic mutations that can lead to cancer. Glass does not protect you from skin damage from the sun. It affects indoor plants too. Have you ever taken an indoor plant outside and burned its leaves? This happens because the plant was unaccustomed to the higher levels of UVA found outside, compared with inside a sunny window.

additionaly: many windows are also treated with an extra layer that tries to block more UVA. Glassware usually des not have that treatment. Also, Plexiglas can be pretty much considered a block for the curing UV-light too.

Yea, they do. I doubt mine does because that's cheap glass :)
Polycarbonate also blocks UV.

Yes.
I frequently leave models made on a Saturn printer with Elegoo gray resin on a surface in the sun to slow cure them. If properly cleaned their finish is indistinguishable from models rapid cured in a UV chamber.
It should be noted that I only do this with small models that are Table top miniature scale. Large models with lots of shadows, overhands or complicated detailing may not cure evenly.
I usually do this if I have a lot of models to cure and am too lazy to keep cycling them through my cure station.


text:
Printer inverted Y-axis
I made a custom printer with RAMPS. I used Y-MIN endstop at beginning. After few prints I discovered that Y-axis was inverted (mirrored).
I fixed Marlin firmware and now I have:
#define Y_MAX_ENDSTOP_INVERTING true
#define INVERT_Y_DIR false
#define Y_HOME_DIR 1
#define USE_YMAX_PLUG

I also connected the Y-endstop to Y-max pin on RAMPS.
Now the printer homing in the same direction than before (in front) and the y-endstop works as expected.
If I try to start printing or if I try to press the "center" button in Pronterface, the Y-axis moves in the wrong direction.
Can someone help me?

When facing your printers Y-axis (so from the front), where is the Y-endstop located? In the back or in the front? Adding a sketch may help.

the Y-endstop is in front and the motor is in the back.

This blog post shows 3 main solutions:

Flipping the motor cables (As suggested in the other answer)
Switching the x and y-axis:
This may switch the direction of your y-axis depending on the way your printer is setup)
Change the direction of the axis in firmware which you can see below how to do:

"When the solution opens up, you will see many different files open. You need to navigate to the Configuration.h file. Within this file scroll down to the following lines of code:"

// Invert the stepper direction. Change (or reverse the motor connector) if an axis goes the wrong way.
define INVERT_X_DIR true

define INVERT_Y_DIR true

define INVERT_Z_DIR true

"This is where you need to switch the values around. If they are currently true, change them to false and if they are false, change them to true. Due to the fact I was having issues with my x-Axis, I have changed the above to the following:"

// Invert the stepper direction. Change (or reverse the motor connector) if an axis goes the wrong way.

define INVERT_X_DIR false

define INVERT_Y_DIR true

define INVERT_Z_DIR true

Usually I just flip the connector around on the board. This causes the stepper to reverse without fiddling around with firmware.