I designed a part using CAD software to combine it with a mechanical component which already has holes on it. The locations are correct as I have the CAD file for that component from the manufacturer.

I 3D printed the part and added threaded inserts. When I tightened the screws to put the 3D printed part and the mechanical component together, often I had difficulty in tightening 1-3 out of about 10 screws. When I removed the two parts, sometimes there were scratches or lost paints around the holes of the mechanical part. What are the causes and how to make it easy to tighten all screws?

  • $\begingroup$ It sounds like tolerance errors - probably on the printed part. Consider using one reference hole with a tight fit and make the rest slightly larger. $\endgroup$
    – Transistor
    Dec 3, 2022 at 0:03
  • $\begingroup$ Fit dowels for alignment, then screw holes can be larger. $\endgroup$
    – Solar Mike
    Dec 3, 2022 at 8:30

1 Answer 1


It sounds like tolerance errors - probably on the printed part.

Consider using one reference hole with a tight fit, another with a short slot in the radial direction from the first hole so that it will be an easy fit butthe part can't rotate and make the rest slightly larger to provide some extra clearance. The latter holes will be used for holding but not for alignment.

  • $\begingroup$ Thank you. Could you please clarify what you mean by "short slot in the radial direction...can't rotate"? Also, do you mean I should not make all the holes a very thigh fit since 3D printed parts cannot be exact? Problem is if I make the holes bigger, they cannot grip the threaded inserts tightly. If I make them smaller, some filament will block the holes as I put in the thread inserts. $\endgroup$ Dec 3, 2022 at 0:57
  • 1
    $\begingroup$ Sorry, see where the confusion arises. I meant the slot and enlarged holes to be in the mechanical component. See reddit.com/r/MechanicalEngineering/comments/iccp32/… for some more explanation. $\endgroup$
    – Transistor
    Dec 3, 2022 at 17:14
  • $\begingroup$ Thank you. Is my problem caused by the so-called bolt crosstalk? $\endgroup$ Dec 4, 2022 at 0:25
  • $\begingroup$ I've never heard of bolt-crosstalk. It just sounds like tolerance errors to me. $\endgroup$
    – Transistor
    Dec 4, 2022 at 14:00
  • $\begingroup$ @lovedrinking do you mean that the bolts were cross-threaded? $\endgroup$
    – jsotola
    Apr 26 at 7:57

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