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Warping on a large, flat print surface  

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ncprintr
(@ncprintr)
Active Member
Warping on a large, flat print surface

I am using a Mk2 printer with the grey Prusa filament that came with the printer.

I am trying to print a simple storage container for organizing screws, nails, bolts, etc. It's about as simple a print as you could imagine. A flat square surface with a grid of wall to make a number of cells. When I start the print, the base of the box prints in three rows of filament. The first two rows go down without a problem. But the third row bubbles and warps up in a square area roughly at the middle of the print. The outside edges of the print are unaffected. I have attached photos of the second attempt at printing the box, where I stopped the print after the base bubbled up:

On the third try, I just let the print run to see what would happen. The box was surprisingly still able to print despite the base layer warping. Still, I would like to print the box with a smooth bottom and want to get to the root of whatever this issue is. Does anyone have an idea of what is going wrong here? Here is a photo of the finished box with warped base layer (viewed from above):

Posted : 22/02/2019 5:46 pm
kevin.r5
(@kevin-r5)
Estimable Member
Re: Warping on a large, flat print surface


The first two rows go down without a problem. But the third row bubbles and warps up in a square area roughly at the middle of the print.

Do you mean the first two layers are ok, and the problem starts on the third layer?

Can you post the STL you're printing?

-Kevin

-Kevin

Posted : 22/02/2019 6:13 pm
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Correct. The first two rows print properly and the third bubbles up.

The STL is on my home computer, so I'll post it when I get off from work. Thanks!

Posted : 22/02/2019 7:15 pm
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

I'm trying to post the STL, but the attachments manager doesn't like the extension. Looks like it's just set up for posting images. Any suggestions on how to post it into the forum?

Posted : 22/02/2019 11:47 pm
kevin.r5
(@kevin-r5)
Estimable Member
Re: Warping on a large, flat print surface

Just put the STL in a ZIP file and you should be able to attach it.

-Kevin

Posted : 23/02/2019 3:54 am
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Thanks, here it is:

Posted : 23/02/2019 5:50 am
kevin.r5
(@kevin-r5)
Estimable Member
Re: Warping on a large, flat print surface

The model is very small (20mm x 17.5mm x 5mm with .1mm thick walls). Other than that, I can't find anything wrong with the STL.

I scaled it 10x in Slic3r (200mm x 175mm x 50 mm with 1mm thick walls) and it seems to slice ok.

Scaled it 5x and the third layer looks strange - it doesn't cover the entire base of the model:

I'm not sure what's causing this - perhaps a rounding/math/precision error from scaling in Slic3r. I tried Windows and Mac versions of Slic3r and the result was the same.

ncprinter: what size are you trying to print this at?

It might be better to make your model at the desired size instead of scaling it in Slic3r.

I'm not sure what else to suggest - if your first and second layers are both good, it doesn't seem like a problem with your printer.

-Kevin

Posted : 23/02/2019 5:58 pm
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Thanks for looking at the model and giving your feedback. The box is supposed to be 200mm x 175mm x 50mm. I modeled it that size, but when I export the STL from my modeling program and put it in slic3r, it always shrinks to 10% (I have no idea why it does this), so I have to scale it 10x to make it back to the size it's supposed to be. I printed it at the 200x175x50 size.

I guess I can try to change the thickness of the base of the box and see if that helps. 1mm is adequate for the what the box was intended for (holding nails, screws, etc), but maybe not ideal from a printing perspective. I'll play around with the thickness and see if the problem goes away.

In the meantime, if anyone can tell me why slic3r always shrinks my STL's down to 10% and maybe how to prevent that from happening, I would be really grateful!

Posted : 23/02/2019 9:35 pm
kevin.r5
(@kevin-r5)
Estimable Member
Re: Warping on a large, flat print surface

Sorry I couldn't be more help.

If I load your STL and scale it 10x it seems to slice fine at .2 and .35 layer heights. I'm guessing you're using the .35 layer height if the 1mm base is producing 3 layers.

You could try reducing the speed using the knob on the printer until you get past the third layer. Or possibly slice it at .35mm layer height and change the first 1mm of the model to print at .2mm layer height.

It just puzzles me how you could repeatedly get 2 good layers then it screws up on the third layer.

As far as your model changing scale when you import it into Slic3r, I think Slic3r is uses millimeters as it's unit of scale. Is your modeling program is set to us centimeters as the default unit? Or perhaps there is a setting for scaling when you export objects.

-Kevin

Posted : 23/02/2019 11:47 pm
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(@)
Illustrious Member
Re: Warping on a large, flat print surface

It looks like bed contamination. First layers lay down, but aren't sticking well. When the third layer hits, the temp differential starts sucking up the bad layers below. I've had this happen a few times. A good wash resolves it.

Theory: First couple of layers are kept warm (>50c), and third layer (or higher) is insulated enough the bed heat isn't reaching it, and when it cools below 50c, the thermal stress begins torquing on the lower warm layers. Areas where there is better adhesion, the stresses can't pull up.

You can test for this by printing just layer 1, and if the filament is at all translucent, you're looking for any spots with a discoloration.

Posted : 24/02/2019 1:20 am
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Well, I gave the bed a thorough cleaning and tried to print with just two layers, since those had stuck before. That failed even worse. 😯

I tried printing a single layer, as suggested by tim.m30 (also attached below). I actually printed one layer and a bit of the second just to see how they compared. Most of the initial layer printed well, but holding it up to a flat light, you can see that in one corner the filaments were not connecting well. In fact, on the print holding that section you can feel the threads coming apart as you run your fingers over them. On the small section of layer two that did print, you can see layer two start to bubble as it nears the center rectangle that seems to be the most problematic area. That bubbling occurred in an area where the layer one filament had actually printed quite well. The layer 1 threads were well adhered, but the layer 2 threads were clearly not sticking to them well. Inserting a thumbnail between the layer 1 and 2 threads, they come apart very easily. This is quite frustrating. Something isn't working well, but I don't know what it is. And on such a simple print, too!

I'm having difficulty adding the photos for the layer test. I'll try again in a second post.

Posted : 03/03/2019 5:31 pm
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Here are the layer 1 test photos

Posted : 03/03/2019 5:32 pm
lee.g
(@lee-g)
Estimable Member
Re: Warping on a large, flat print surface

This is a common problem with the 0.35 layer height.

I won't go into the mechanics but you will likely solve the problem by altering the profile and making it 0.3mm instead. My preference for fast prints is my 0.25mm profile with wider extrusion width. Still not as fast as the 0.35mm profile but pretty fast and great print quality.

Some machines are finicky with the 0.35mm profile. Some work some don't. My machine actually works with it but i don't use it because of weak layer bonding.

Posted : 03/03/2019 5:43 pm
bobstro
(@bobstro)
Illustrious Member
Re: Warping on a large, flat print surface

I'm not sure what layer height OP is using, but layer heights should not exceed 80% of nozzle size. Otherwise, you print extrusions with a cylindrical cross-section that will have very poor inter-layer adhesion. With a 0.40mm nozzle, keep layer heights to 0.32mm or lower for best results.

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 03/03/2019 5:56 pm
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(@)
Illustrious Member
Re: Warping on a large, flat print surface

From Prusa (in the Mk3 profile): pretty sure it isn't printer specific. I once tried 0.35 and won't do that again.

Here's a properly dimensioned version.

Bed temp should be tweaked to 65c (or higher) for this part in PLA or it will warp and lift in the corners.

Posted : 03/03/2019 7:27 pm
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(@)
Illustrious Member
Re: Warping on a large, flat print surface

If washing the bed makes adhesion worse: then the wash process used is bad. I once used my dish sponge to clean the bed: that was a terrible mistake. I now use only fresh paper towels, and I also reduced the soap I use to a few drops because I have a water softener and soap doesn't rinse off well.

The second set of layer ones look like they are much too high. Strands aren't even welding. Getting layer 1 right is crucial to any print success.

Posted : 03/03/2019 7:30 pm
ncprintr
(@ncprintr)
Active Member
Topic starter answered:
Re: Warping on a large, flat print surface

Thanks for all the suggestions. I tried a 0.20 layer height and turned up the bed temperature a bit, and that did the trick. Perfect print this time. Appreciate the help!

Posted : 26/03/2019 2:31 pm
Background
(@background)
New Member
RE: Warping on a large, flat print surface

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Posted : 03/06/2019 8:45 am
DarcShadow
(@darcshadow)
Trusted Member
RE: Warping on a large, flat print surface
Posted by: ...

If washing the bed makes adhesion worse: then the wash process used is bad. I once used my dish sponge to clean the bed: that was a terrible mistake. I now use only fresh paper towels, and I also reduced the soap I use to a few drops because I have a water softener and soap doesn't rinse off well.

The second set of layer ones look like they are much too high. Strands aren't even welding. Getting layer 1 right is crucial to any print success.

Just to clarify the water softer statement, it's not that the soap doesn't rinse off well because of the softwater. It rinses the same with hard water, the difference is the minerals in the hard water stick to the surface and eliminate the slick soap feeling, the soap is still there, it's just contaminated with the minerals from the hard metal.

Posted : 03/06/2019 2:19 pm
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