Hole size already compensates for shrinkage?

Mostly Printed CNC - MPCNC Advice
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Hi all. What a great project and community! I have a question about the STL files for the printed parts. My printer as tuned underprints the ID of holes by around 0.3mm. Extrusion width is correct (0.9mm width for two 0.45mm perimeters, outside dimension 20mm cube is spot on 20mm). Software is set to use lots of edges to approximate the circle, etc. I’ve read about lots of reasons this can happen (plasting shrinkage, pileup of plastic on the inside of curves, slicers putting the middle of the printhead on the line rather than the edge…), and it seems like folks mostly live with it by either bumping up the drawn dimensions in their CAD tool or by drilling the hole.

My question is how much shrinkage of the holes is already accounted for in the STL files? I pulled the new foot into Fusion 360 and see that the main hole is 23.71mm in diameter. Is this meant to be printed the same dimension as drawn and allows for variation in the conduit OD, or is this allowing around 0.2mm shrinkage for the 23.5mm pipe? If I print this with my setup as is, the hole will be around 23.4mm diameter. Do I need to make adjustments in my slicer?

 

Thanks,

 

David

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It should work as is.

I tried to account for the vast majority of printers that undersized holes, but at the same time the part has flex as well. OD is more important, get that right and everything should be good.

A kind of odd thing we have been looking at lately is skew, or non square prints. If you print a large 100x100 square see how close the diagonals are. I am willing to bet this could account for some of the vary early (first few months) crooked MPCNC’s. Don’t go too crazy trying to fix this the numbers are amplified so it won’t actually be as bad as it seems. Some super cheap printers can be pretty far off and usually easily fixed.

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