TL;DR: Advice on how to machine/refine studs and +-axle holes on home made Lego-compatible parts.

I've been really enjoying designing and 3D-printing my own Lego-compatible custom parts to supplement my collection of official Lego parts. But I'm finding it very challenging to get a half-decent fit.

Round axle holes are OK, a 3/16" imperial drill bit seems to be perfect. So I print 'em a little small and drill them out with a handheld pin vise to get a really nice smooth bore.

I'm having a much harder time with studs (knobs) which I simply have not found a good way to print slightly oversize and machine down neatly. So I'd love some ideas.

I'm also looking for suggestions on how to make "+"-axle holes that deliver a satisfying fit. I know the official parts have small "ramps" on the edges to give a better friction fit, which isn't very practical for me to make. But right now I'm stuck filing out the axle holes by hand, which is a slow, difficult and inaccurate process. Any advice on a good way to cut or trim them would be extremely welcome.

At this point I cannot achieve the dimensional accuracy required to get a really good fit straight off the print bed, though I'm working on that too. So I'm relying on erring on the side of too much material then removing material in post-processing to get the desired fit.

Related engineering.stackexchange.com post

  • From what little I know about 3D printing, you're going to have to use an extremely small nozzle to achieve the accuracy (aka tight tolerances) you need for the "lego" parts you're printing. I also understand that this drastically adds to the time of each print, but would save you the time of drilling, sanding, etc. Sorry I couldn't be more helpful.
    – JohnnyB
    Commented Sep 5, 2019 at 12:42
  • 1
    Better yet, search the site - bricks.stackexchange.com/search?q=3d+printing
    – JohnnyB
    Commented Sep 5, 2019 at 13:03


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