Bulge when print reaches "solid" layers  

RE: Buldge when print reaches "solid" layers

Posted by: tim.m30

Voj, not entirely sure I agree - I see all three of your numbered effects in that print. The edges and corners are key points to examine. I also see what appears to be almost random seams rather than rear seams - either that - or your filament is wet and sputtering.  What you are describing as directional effects may be simple speed variation due to acceleration time; especially when the texture also changes when the larger area ends, and the Slic3r invokes a different speed in those long strokes along the back, between the hole and the full box layers: you wouldn't be the first person to invert the Slic3r slow down logic..

The printer is straight from a dryer. It's quite boogery (there's filament accumulating on the nozzle and randomly falling off), my other PETG's don't do that this much. But it is not sputtering. And yes, the seams, although set to 'rear' are (in addition to rear) all over the place. Keep in mind that because 'External layers first' is set, you'll see all of retraction-unretraction-coast artifacts on the print - one of the major disadvantages of doing external layers first.

Regarding acceleration, the whole print shows in dark blue in the speed preview, same color everywhere, around 16mm/s limited by the volumetric speed parameter. At this super slow speed, I don't think acceleration plays much of a role. But I can go even slower to test.

As to the artifacts, you're right. Using the caliper, the object has 49.80mm external dimension in the infilled part, 50.30mm in the solid infill area and 50.15 in the solid wall area. This is actually worse than the default 0.2 SPEED profile at 49.9/50.15/50.10mm. It just looks better thanks to being glossy. Good point about having to watch the edge.

RE: Buldge when print reaches "solid" layers

Posted by: Vojtěch

The printer is straight from a dryer.

Eh, the filament is taken straight from a dryer.

RE: Buldge when print reaches "solid" layers

Voj: If you look at the slice in detail, the external perimeter has no more retracts if laid down first or second or third. Generally the tool follows the perimeter, then steps sans-retraction one perimeter width sideways to do the next perimeter. And you get a retraction on the last point when external is last, and no visible retraction point when outside perimeter is printed first. I doubt the marks are retraction artifacts.

And seams - at least when I printed the part with rear seams, all were 100% behind the visible face, with a few at the hole level at a corner I did not expect; and most certainly there were no seams in the middle of a surface.  Only time I've seen that is with random seams.  So that's why I mentioned moisture in the filament -- and it wasn't a condemnation: I was just making an observation.  Printing is one of those hobbies that requires continuous learning: and sharing ideas is a great way to learn that I enjoy. 

Jerk and acceleration play a major role in printing this part. The print speed shown in the layer preview is not entirely accurate. Set external and small perimeter speeds to 20 mm/s with perimeter accel to 400, and observe the final sheen.  Also, make sure Filament>Cooling>Layer Print Time... is set to 1 second.  

RE: Buldge when print reaches "solid" layers

Another data point. Same object (1.35mm wall), 0.20mm speed profile, ColorFabb PA-CF Low-Warp Nylon. Spoiler: Exactly the same result as with PETG.

RE: Buldge when print reaches "solid" layers

And one more. Very warpy (high coefficient of thermal expansion) Fillamentum Nylon CF15. I guess this definitely rules out thermal issues, since the result is very much identical to the previous low-warp Nylon.

RE: Buldge when print reaches "solid" layers

Posted by: Vojtěch

And one more. Very warpy (high coefficient of thermal expansion) Fillamentum Nylon CF15. I guess this definitely rules out thermal issues, since the result is very much identical to the previous low-warp Nylon.

Are you using the Prusa profiles? I re-ran my 1.35mm wall test using the Prusa QUALITY and my personal profile, this time with the long face along the Y axis. I seem to be getting results consistent with my prior tests. The Prusa profile produced the bottom result, my profile the top. I forgot to re-orient the z-seam, visible at left.

RE: Buldge when print reaches "solid" layers

Here a hopefully undistorted image:

RE: Buldge when print reaches "solid" layers

@Bob:

Yes, this is default Prusa 0.2mm SPEED profile for both the Nylons. Somewhat speed limited by the filament max volumetric extrusion speed of 3mm³s⁻¹ (due to carbon fibres). I did want to use a profile that shows the problem to see if the results are material (thermal expansion) dependent or not. I was not trying to minimize the issue.

Now I'd like to try with your profile, but the AMF file doesn't include it, I'd need your 3MF instead.

RE: Buldge when print reaches "solid" layers

@tim-m30: Just printed slow and with low acceleration as you suggested (and a bit hotter, too). The surface is all shiny and beautiful, but all the artifacts are still there. Measuring with a caliper, the shape of the object didn't change the slightest bit.

RE: Buldge when print reaches "solid" layers

And the picture after a very slow print:

RE: Buldge when print reaches "solid" layers

Wall variations ... random seams ... slow vs fast.

RE: Buldge when print reaches "solid" layers

Posted by: Vojtěch

[...] Now I'd like to try with your profile, but the AMF file doesn't include it, I'd need your 3MF instead.

I had not realized that "Project" = 3MF in Slic3rPE. I've attached a 3MF and config just to be safe. Thanks for pointing that out.

Oh... can we only attach a single file now? Yet more fun with the new forum software.

RE: Buldge when print reaches "solid" layers

Posted by: bobstro

I've attached a 3MF and config just to be safe. Thanks for pointing that out.

Thanks! I'll give them a spin once I get home again (and put my printer together ... upgrades).

RE: Buldge when print reaches "solid" layers

@Tim:

The random seams variant looks pretty uniform ... except for the seams, of course.

RE: Buldge when print reaches "solid" layers

@Bob: After completing my printer upgrades and verifying they do improve print quality (wall horizontal smoothness), but not the wall shift/thickness effects, I've used your profile, did one additional tweak (External perimeters first), used a better PETG (Fiberology PETG Onyx) that's less oozy, stringy and boogery, et voilà:

The surface is almost flawless. I can still measure a 0.04mm bulge corresponding to the solid infill layers, but I can't see it unless I reflect a strong light under just the perfect angle.

Now this comes at a cost. The top layer with the numbers suffered a bit, the back seam is rather ugly and I'll still need to tweak the retraction settings. There is some filament lost during coasting and I'll need to offset that. There is always some underextrusion after unretraction, making the seam look bad.

So, thanks for your profile, now I'll need to dissect it and find what makes the most difference. I believe one major bit is the 'detect thin walls' checkbox enabled, which allows Slic3r to extrude non-standard widths to fill non-integer gaps in walls. But it also affects perimeters, damaging the lettering. I know that eg. S3D does width manipulation routinely and that could be one of the reasons why it slices these test objects better.

If I may ask for more: Your profile references two Python post-process scripts (and fails without them), would you share them, too?

RE: Buldge when print reaches "solid" layers

As I recall, when I was comparing gcode, a file that resulted in issues had the exact same extrusion code in the external perimeter as a fie that caused no issues.  So extrusion start and end points and amounts were identical: Only speed was different.

RE: Buldge when print reaches "solid" layers

Since oozing depends on speed, retraction strategy should probably be speed dependent, too. We already have the Linear Advance to compensate for elasticity of filament, but now I wonder how it interacts with retraction and retraction settings.

RE: Buldge when print reaches "solid" layers

There is another thread dealing with linear advance ... and somewhere in the Prusa blogs is a simple test for it.

Here's one place to look: Lin Advance / K-factor

RE: Buldge when print reaches "solid" layers

Posted by: Vojtěch

[...] If I may ask for more: Your profile references two Python post-process scripts (and fails without them), would you share them, too?

I keep forgetting that. I've attached the config without the post-processing scripts.

Here's my page with the bumpfan script to kick the fan speed to 100% before setting it lower. It should probably hold 100% momentarily, but this helped me with using lower fan speeds.

Here's a raw dump of the file renaming script to embed print info into filenames.

I was experimenting with a number of post-processing scripts at the time. They're not super-useful.

RE: Buldge when print reaches "solid" layers

Posted by: Vojtěch

Since oozing depends on speed, retraction strategy should probably be speed dependent, too. We already have the Linear Advance to compensate for elasticity of filament, but now I wonder how it interacts with retraction and retraction settings.

I put together some basic LA testing described here that might help get started.

I'm finally getting ready to start doing some more testing with PETG. I'm curious to see how it works with the LA test tower.