Help with surface quality on Printrbot Metal Simple

[JoelM]

I am having a hard time getting rid of zits and blobs on the surface of my prints so I thought I'd reach out for help.

I'm printing on a Printrbot metal simple with PLA. I've calculated my Esteps, measured my filament diameter and printed solid 20x20 mm cubes to dial in my extrusion multiplier. So with that info and starting with the default metal simple profile I've been printing test print after test print without any improvement.

To eliminate the blobs I've set my retraction settings to 1mm retraction, 80 mm/s speed. I've tried combos of coasting, wiping, negative restart distances... nothing seems to help. Printing at 210 C ar .3mm layer height for now.

I've tried a few different filaments as well and I get the same results for each one. When I first got my printer I was getting great results with a half spool of white from printrbot but ran out and had some hardware issues. I've replaced both of my gt2 belts as one snapped and the other wore out in the center. I've tried 2 metal ubis hot ends but they both jammed so I sent them back.

I know the printer can do nice prints, I just have had nothing but bad luck with mine. Any ideas or suggestions would be appreciated.

[JoeJ]

210 is pretty hot for PLA. Dropping that some would help reduce oozing. And coasting and extra restart distance both make a big difference. So I would still recommend experimenting with them.

If it helps, it looks like there's a new guide out that specifically talks about this stuff: https://www.simplify3d.com/support/prin ... s-and-zits

[JoelM]

Thanks for the reply Joe.

I normally print at 190 C so I did another test print at 190 with coasting set to .2, extra restart distance -.2 and wipe distance to 5mm. I still get really ugly retraction seams.

From what I observed, the inside perimeter goes down fine with a negative restart distance but when the extruder shifts over to print the exterior perimeter I see a bulge before it returns to normal. With the extra restart the inside perimeter even looks like a pencil tip. Going from nothing to full length.

I'm attaching my fff setting and images of what I'm still getting and a close up of what I was getting earlier this summer. My filament diameter is 1.67mm and my multiplier is set to 8. Seems weird to me but it works for my volume cube test.

Thanks for looking.
Joel

Printrbot Simple Metal.fff

(11.14 KiB) Downloaded 388 times

[JoeJ]

Ok, so the problem isn't occurring at the start of the perimeter? but instead the blob shows up at the end? In that case, I would use some coasting. That will help relieve excess pressure which frequently causes dots at the end of the perimeter when it closes off.

You can find plenty of other suggestions and explanations in their new great guide: https://www.simplify3d.com/support/prin ... s-and-zits

[JoelM]

Sorry for not being to clear. It is at the beginning of the perimeter but the inner perimeter looks fine. Just the outer start gets a blob. I drew up an illustration showing what's happening.

[dorgeman]

Hi Joel,

I would be concerned that the multiplier is at 8 - it should be something just a little less or more than 1.0. That is especially true if you already calibrated e-steps.

There are a lot of things that could cause what you are seeing. Here are some possibilities in no particular order:
1) temperature too high - even if the number you set it to seems reasonable - could be a bad thermistor selection in firmware
2) the retraction might be insufficient - if not enough filament is pulled back, then what is left in the hot zone could melt and ooze out
3) retraction speed might be too fast and might cause skipped steps or stripping - then the filament would not consistently move back as much as you think it is
4) z raise might be too slow leaving the hot end sitting in one spot too long - that can melt plastic in place and also ooze while going

I am sure that there are more possibilities, but that is what I have off the top of my head.

I would recommend that you try printing my deterministic retraction object from Thingiverse. You will, however, have to use slic3r to do it. I have not yet been able to find Simplify3D settings that will print it to print the way you need it to. (BTW - if anyone knows settings that force Simplify3D to print it in only one direction, please let me know.) Watch it while it prints. Can you visually see the Z lift? If so, it is too slow. Do the final parts have blobs at the reload point, or the retract point, or just the Z lift point? Do you have stringing on any of the various length gaps? Anything other than a clean print for all gaps should give you valuable clues to what is happening.


-David

[JoelM]

Thanks for the reply David. I am concerned about the multiplier being so low. I'll be starting over from scratch when I have a chance. I feel like I must have done something wrong at some point. The blobs seem to happen when the extruder moves to the outer perimeter, almost like it overshoots it's travel move.

Do you have a link to your retraction object?

Thanks again.
Joel

[dorgeman]

You can find the retraction test at:

http://www.thingiverse.com/thing:1065179

When it prints properly, the hotend will start at one end of the vertical fin, move to the gap, retract, cross the gap, reload, and then go to the end of the fin. It needs to do that across all copies - and I generally print 3-5 of them with different gap sizes at a time.

Based on your drawing, my first guess is that the problem is Z-lift is too slow. I had that problem before I started working on tuning retract. I ended up changing the jumper switches on my Z motor driver to 1/8 micro-stepping. Then in firmware, I decreased the steps per mm and kicked both Z acceleration and Z feedrate up from what they had been. I pushed those values as high as I could without losing steps. Afterwards, the Z lift was imperceptible. If that is your problem, then the gaps in the test object will look perfect, but there will be blobs on the end of one of the plated parts (where the z lift occurs). If you see the blobs on the retract or the reload side of the gaps, then it is something else.


-David