Problems with the accuracy from holes in my 3D Printing


Hey Guys,

i’m really new in 3D printing (bought my Anycubic i3 Mega in december 2018), but i learn very fast. For a special problem, however, I need your help. :wink:

First of all, i did a extruder calibration. I printed a cube with a single wall and set my multiplier in Simplify3D for a nearly perfect 0,4mm thick wall. I printed also a cube for measuring, but when i calibrate it only for 20x20x20mm (toleranz +/- 0,02mm) and printed a larger object (150mm) the accuracy was terrible. So i did a mix for larger and small objects. A 20x20x20mm Cube is (example) 20.03x20.02x19.99mm and over a larger straight about 100mm it is 99.95mm.

BUT…when i printed a 10mm hole within the object, the hole is only 9.80mm. The mesh from my CAD Software (FreeCAD) has a high resolution, so this is not the problem…i hope. :wink:
For a workaround, I could increase the radius of the hole by 0.1mm. But i actually only bought the 3D printer for building Actuators for my Simracing Rig. When printing these components, accuracy is pretty important.

What can I do and why is the accuracy only for holes so “bad” … or is it normal for a printer in this price range?

I print with PLA … I almost forgot to mention.

Thank you in advance, Oliver



That sounds about right, you need to determine the offset you need to apply to get the size hole with the fit you want. Mine is 0.15mm.



Ok, that sounds it is not a problem with my own 3D printer, but a general problem in 3D printing. Is that right? Or, for example, is the accuracy of a Prusa i3 MK3 generally better and does not need an offset for holes by the CAD design?



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@moorviper That is an explanation! :grinning: But to put it in a more simple way, when a slicer creates a path for the extruder, it may do one of three (or more things).

  • Extrude on the line.
  • Extrude outside of the line.
  • Extrude inside of the line.

If your wall thickness is 0.4mm, it has to go somewhere. This will affect the overall dimensions. Some slicers will let you select where the extrusion goes, so that may help.

The other solution is to simply drill out the hole after printing. If you have more than one shell, you should be fine.

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Thanks for the link and description. :slight_smile: Then I’ll probably convert the STL files intended for the Actuator back into solid CAD models for now and then add the required offset. :+1:

Which slicer has this options?

EDIT: OK, I did some research on my lunch break and I’m going to print some tests tonight. In slic3r it calls “XY compensation”, in Cura “horizontal size expansion” and in Simplify3D “horizontal size compensation”. If I understood this correctly, I could make significant improvements without altering the STL file.



It actually seems to work so far. I set the “horizontal size compensation” in Simplify3D to -0.07, so that a 10mm hole in the CAD file was actually 10mm printed too. But the outer dimensions of the cube also shrank quite slightly.

After adjusting the X Y sizes via G-Code (M92), the outer dimensions were back in shape and the size of the hole remained constant at 10mm.

But I’m going to do more test prints with bigger dimensions for myself. I want to be sure that the dimensions are then also in an area that is acceptable to me.

Thanks again for the link and description. That helped me a lot to understand it a little more…i hope :wink:

Regards, Oliver



I mostly use M3 screws so i have calculated the values vor screw in and fit.
And when you put a thread in a part in fusion360 as example it just fits



Of course, if you design something yourself in CAD, you can take that into account. I can also convert existing STL files and edit them via CAD. But I was also interested in why that is. Why are holes in 3D prints a little smaller?

Your Link was perfect… :wink: