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I'm trying to print the following model:

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I'm using Simplify3d to print the model with the following settings on my Qidi X-pro:

  • Filament is ABS
  • Bed temp is 100 °C
  • Extruder temp is 230 °C
  • 1 top layer
  • 1 bottom layer
  • 4 perimeter shells
  • The outside direction is 'outside in'.
  • Internal infill is triangular at 60 %.

I've tried numerous tweaks to the settings, but, I can't seem to get a perfect perpendicular exterior wall as seen in the photos. The print more resembles a trapezoid. It appears like the walls are bowing inward. This also seems to throw off the dimensions. They aren't consistent. For example, the height of the part is 6 mm, but, in measuring with a caliper it shows 5.8 mm to 6.2 mm.

Can anyone tell me how I can get my external walls perpendicular?

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You may be getting shrinking due to cooling on the non-top and non-bottom layers. Sixty percent infill is rather substantial. I'm printing 20 hour pieces in ABS at 100 °C / 250 °C using ten percent infill and getting nothing like what your image shows.

Can you do with a lower infill? More isn't always stronger. Four perimeter shells may be a factor but you'll probably see a difference with a smaller percentage infill.

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  • $\begingroup$ Thanks for the reply. I will be trying with a lower infill. $\endgroup$ – rrirower Apr 27 at 17:31
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If your object doesn't need to be flexible and can tolerate a more brittle material, PLA has better dimensional accuracy. Thus, it would be easier to get your desired shape.

Try two perimeter shells, but slow down the print speed of the perimeter.

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    $\begingroup$ Actually, I've tried with PLA, and, the results are better, but, not perfect. $\endgroup$ – rrirower Apr 27 at 17:32
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ABS shrinks about 1.5% as it cools from print temp to room temp. If your setup doesn't automatically account for this, you can scale up your STL 1.5% before slicing.

I also recommend more top layers - I usually use 4 for 50% infill or greater, and 6 or 8 for lower infill percentages.

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  • $\begingroup$ Thanks. I've already adjusted for .08%. I'll take a look at bumping that up and adjusting the layers. $\endgroup$ – rrirower Apr 28 at 13:34
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Already mentioned in an answer is that ABS has a relatively large percentage of shrinkage (about 1.5 %), this should be encountered for in your model. So, the top layers width being smaller than the model is perfectly explained by the shrinkage.

It is also this shrinkage that causes the excess width layers at the bottom in combination with the heated bed temperature. The bed is of relative high temperature, this is close to the glass temperature of the filament, this ensures that the plastic is soft and adheres well to the build plate. But, this high temperature also causes that the material doesn't shrink much (the cooler, the higher the shrinkgae), the further away from the bed the lower the temperature the higher the shrinkage. This causes each layer to be a little smaller than the previous layer. As the part progresses layers are build upon layers fixating the layers, so the material at the lower layers will not shrink back when the whole part is cooled down (it will probably cause for some compression stress in the lower region).

This defect is known as "elephant foot" as e.g. explained in this answer. Basically the bed temperature is too high (but the downside is that ABS needs a high temperature to prevent warping and loosening from the build plate), too less cooling (also not something you want when printing ABS as cooling causes warping and prevents layers to stick well to each other) or a too low distance between the nozzle and the build plate. You could try lowering heated bed temperature by 5 °C each print, print with a raft and increasing the nozzle to build plate distance (leveling with a thicker piece of paper or increase the nozzle by redefinition of the Z=0 plane).

This is a common issue for high shrinkage, high temperature materials. It is something to live with, try to balance out the problem or adjust the print object by changing the design to include a chamfer at the bottom of the print.

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