Thoughts, suggestions on screws and tolerences

I’m modeling an item for my cheapo 3D printer. I’m now experimenting with creating a Plastic M12 screw that screws into the part. In rhino I can boolean subtract to get the tapped hole. However, I assume that would be an exact fit. I’m convinced I need substantial tolerance considering the resolution of the printer. How would one go about adding that tolerance when trying to use a pre-made threaded piece?

Well, considering that the screw thread part is round, you might get away in this case with a Scale2D looking along the axis of the screw. If it’s a 12mm thread, a 98% scale will make the outer diameter around 11.8 (0.2mm clearance) - that may not be enough if your printer doesn’t have high enough res, so maybe 96%, which will make it about a half mm smaller in diameter. The thread pitch should remain the same with a Scale2D, which is important.

Otherwise, you need to model the thread with the clearance built-in - i.e. outer and inner separately with the clearance designed-in.


If you are creating a standard metal M12 threadform, then you can use the Boltgen plugin which includes a tool to scale the inside threadcutter to increase clearance.

However I think plastic threads are usually chunkier so the plugin wouldn’t help if that is what you are wanting.

Thanks for the info on BoltGen! I’ll have to play with it a bit before I know what I’m doing. I’m going to try the scale 2d for now as a test.

I do also use a „cheapo“ printer, I usually print with 0.1 mm resolution, but whenever I want to stick something into another something, I keep a gap of 0.3 mm(!). For screws I always use a screw-nut system (don‘t know the right translation). I bought cheap black screws online which perfectly match my black pla.
I remodeled them with an additional offseted cylinder and just boolean substract this cylinder. I wouldn‘t print screws, this is impossible due to tolerance and the very cheap price (if bought online) doesn‘t need you to do this at all

If using a standard thread you could make the object with plain holes and hand tap the threads.

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