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I uploaded a 3D object for this project to Fusion 360 and printed it out straightforward:

enter image description here

Yet its middle hole is too small for the stepper motor (Nema 17 Stepper-M) I am using so I wanted to increase its tolerance before reprinting it.

So, I followed the tutorial by Tyler Beck of Tech who lead me to drawings:

enter image description here

I was wondering if doing a drawing (sketch in Fusion 360) was sufficient to expect the shaft of the step motor to go through?

Here are the gear and the shaft before I add the drawing constraints:

enter image description here

enter image description here

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  • $\begingroup$ When you say "its middle hole is too small for the step motor" are you talking about fractions of a millimeter or several percent smaller? $\endgroup$ – agarza Mar 14 at 21:54
  • $\begingroup$ Is this a Fusion problem or a problem with your printer. I would expect the latter to be the culprit. $\endgroup$ – 0scar Mar 15 at 8:02
  • $\begingroup$ @agarza fractions of millimeter, I would say one millimeter max. I will upload a photo soon. $\endgroup$ – Revolucion for Monica Mar 15 at 9:31
  • $\begingroup$ are you sure that that is not a print error? $\endgroup$ – Trish Mar 15 at 21:18
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    $\begingroup$ A digital caliper is a very useful tool to use with 3d printing. Sometimes when printing, smaller features like holes don't come out exactly the size you need, and the caliper will let you measure what change is needed in the drawing. Or you can just guess at the needed change and print another one at the new size and if that doesn't fit you will have a better guess for the next iteration. $\endgroup$ – Andrew Morton Mar 15 at 21:37
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Besides offsetting the clearances you want into models, you can and should also calibrate your printer to compensate for included holes - because often inner holes are solved to be smaller than actually designed out of necessity.

However, the option can also be used to fix problems that stem from the slicing and printing itself, and thus offers to fix some problems that are endemic to your setup or where you can't easily fix the model by setting an offset to create the wanted clearances in it.

In Ultimaker Cura, the option for this fix is called Hole horizontal expansion since 4.6 in April 2020, which only affects internal perimeters as I know from testing.

SuperSlicer, a PrusaSlicer branch offers hole_XY_compensation, though I can't quite pinpoint the time when it was added. I guesstimate sometime before October 2020.

PrusaSlicer offers XY size compensation, which does affect outer perimeters. A hole-only is requested almost since that option was available the first time. An attempt to implement a hole-only compensation again appears to be worked on since mid-2020. It seems that in the beginning of March some implementation has been tested.

The first work for such a function was tried by Slic3r before PrusaSlicer was started on, using an Arc-compensation formula in at latest 2009, but the function proved to be overcompensating. As Prusa-Slicer is a fork of Slic3r, some of this work might remain in the code.

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This seems like a tolerance press fit problem and similar to what you will find if you try the same using normal machining operations on a lathe or milling machine.

I print 3 mm clearance fit holes on my Prusa MK3S, meant to fit on 3.00 mm (measured with a digital caliper) stainless steel shafts. The printed parts are from Fusion 360 models, with 3 mm holes by design, converted to STL and then sliced and printed with 0.2 mm layer height. The holes are very close to 3.0 mm and out by 0.05-0.1 mm.

The solution was to make adjustments in Fusion. I left the model with the hole size as 3 mm but then use the Offset Face command on the inside of the extruded hole to make it slightly larger with the required tolerance.

enter image description here

In my case, an offset of 0.05 provided a nice press fit, and 0.1 offset allowed the shaft to closely fit in the hole but loose enough to rotate.

I suggest you create a simple model with a number of holes designed to be the same size and then use different Offset Face numbers to dial in what you need. That way you get to learn what to expect from your printer and its accuracy.

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