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atari1632

Perfect sides, terrible tops.

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Hi there,

Can anyone shed some light on why the tops of my prints are such bad quality? The sides are nearly perfect, almost invisible lines and quite smooth but the tops are very low detail and full of holes.

A few things i've tried: both raising and lowering the temperature by 10 degrees, quadruple checking the filament diameter, slowing the print right down to 40mm/s. I've also tried low balling the diameter number to force a little more extrusion.

To me it looks like both under and over extrusion at the same time, some of the details are slightly "runny" yet there are holes that would indicate not enough material???

The attached was done with Cura RC2. 0.1mm layer height, 0.8mm wall thickness, 0.6mm top thickness, 50mm/s print speed, 20% fill.

Apologies for the blurry phone camera pics.

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Companion cube! I've got tons of these printed already, most of them with a fine top.

I don't see any indication of over-extruding, and all indications of over-extruding. Maybe your tension knob is not tight enough or too tight? (this is pretty important, and hard to get right in the beginning, but after a while you get a feeling for the correct tension)

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Thanks for taking the time to reply but you've left me with a bit of a conundrum...

 

I don't see any indication of over-extruding, and all indications of over-extruding.
:D

I presume you mean I'm under extruding? The filament seems to be pushed quite smoothly and consistently up the bowden tube. There are clear signs of teeth marks from the bolt with no gouging and it's nigh impossible to pull the filament backwards by hand, but I'll try tightening the bolt a bit more and see how that goes.

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The attached was done with Cura RC2. 0.1mm layer height, 0.8mm wall thickness, 0.6mm top thickness, 50mm/s print speed, 20% fill. Apologies for the blurry phone camera pics.

Under or over extrusion should be easy to calibrate via the "extrude 100mm and measure and calculate the E steps" method (standard is around 865.888/mm) and measuring the diameter to 2 decimal points (cheap calipers with 0.2mm precession and one decimal after the point are useless in this context) properly will ensure the right extrusion with cura (and slic3r)...

after you have set those 2 right, you need to face the fact that Cura (and slic3r) are a little bit infill challenged, meaning the regular infill is way too thin, and severely under the nominal 20% in your case (it's more like 10-15% volume). but that doesn't matter since you are printing a decorative item, not a functional piece... the consequential error/problem is that the solid infill on top of the normal infill (which is way too sparse) has nothing to hold on to, falls through and hence looks like it's under-extruded. Since the SF/Cura infill routine is pure voodoo (acording to Daid), nothing can be done about it. Alex (slic3r) also doesn't seem to have this on his list of priorities and/or he doesn't care much about it.

workarounds:

 

  • [*:xwg6nno4]print more solid layers... eventually the gaps from below will be filled (10 layers, or 1mm in your case)

    [*:xwg6nno4]increase the infill rate to 30-50% (depending on your willingness to waste PLA&time)

    [*:xwg6nno4]manually lower the speed via repg control panel or via M220 Sxx (xx means xx% speed) in printrun/printerface for the first 2 solid layers (on top of the sparse infill) to 50-75% print speed... like the bridge speed, and this will allow the plastic to better hold on to the little support it has from below.

    [*:xwg6nno4]use the grid or hexagonal infill pattern in cura (expert settings?), this will create a very strong and solid structure inside (25% should be more than sufficient), good enough to support/print solid layers on top of it at 75mm/s. this will take much longer to print, and make your object unnecessarily rigid.

 

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If you use KISSlicer you can get better looking top surfaces because KISSlicer increases the sparse infill density as the printer approaches the top surface. So if you start out with like 20% infill the three layers right before the top surface will be printed in a 50% infill crosshatch so the top layer has something mostly solid to sit on. Printing more than one top layer is preferable; three has worked well for me (with 0.2 mm layer height)

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