How do you create a working jack screw?

I’ve been having trouble creating a working jack screw that can move up and down by rotating (it should be adjustable rather than just tightening).

My design looks like this. I’ve added cutaways to show the profile of the screw threads but in the complete print both rings go all the way round.

Basically there are two independent cylinders with identical (but spaced) threads on the inside and outside cylinder.

The outer diameter is 52mm. I tried a print with 0.5mm clearance between both threads and the resulting screw is too loose (there’s far too much play), but if I decrease the gap to 0.25mm (as pictured) then it becomes impossible to thread them together, even when sanded down a bit and oiled.

Has anyone made a similarly sized working screw? Is there a better thread profile to use?

Cant you just use metric threads? Just take an m5 thread and enlarge it by 1000% and you have 50mm thread. Use it to cut out the outer ring and join it to the inner ring and you have a perfect working thread.

I have different sized metric threads as stl’s if you want them.

Is there something about the thread profile you think would make them work better? Ideally I’d like to carry on being able to generate them as I can be more flexible with the pitch and dimensions.

Not really. Any pitch or dimension should work, as long as they fit exactly into each other’s slots. The distance between the threads doesn’t have to be a single micron. At least, I never use any space between them and my bolts fit perfectly in my printed threads. However, I never printed my
Bolts. I use genuine ones. Having resin on resin might be an issue indeed.

Perhaps what you can do is create a small hole in the centre piece (in the side) and another one on the outside ring and create a small tool which you can use as leverage. That will make it easier to twist through the treads. . Once gone though the thread once, the prints should be adapted to each other and work perfectly!

All SAE threads use 60° between the two edges, I think you will have much better luck with that. Here’s that angle shown on some threads I made.

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