5/16 - 18 or 3/8 - 16 for z axis

I am working on a new rewrap and I have both 5/16" - 18 and 3/8" - 16 threaded rods on hand.

Would one be better than the other for a z- axis?

Thanks.

Neither.

Use M6 or M8 if at all possible.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

The 5/16-18 is preferable for the finer pitch and not being absurdly oversize, but your optimal layer heights will be an inconvenient size. The metric sizes give more sane optimal layer heights and don't contribute to the perpetuation of inch hardware. M5 or M6 can be coupled to the Ø5mm stepper shaft with just tubing and zip ties. M8 is actually a bit oversize and more likely to contribute to Z axis wobble (Don't overconstrain the screw!).

If you read the article in rep rap magazine issue 2 i think, it explains about recurring z errors due to the steps in the motor divided by the screw pitch. Ie for m6 thread pitch is 1.0mm a nema motor with 200 steps will have 5micron movement for every step.
If you work out an imperial thread it will come out with long trailing numbers and will therefore create a repeating zerror if you use say a 0.1 or 0.2 layer height.
Something to bare in mind when designing a z system.

Quote

If you work out an imperial thread it will come out with long trailing numbers and will therefore create a repeating zerror if you use say a 0.1 or 0.2 layer height.

With a properly working firmware this error won't add up, because Z coordinates are absolute. As such this rounding error doesn't matter at all, because accuracy in the below-1-micrometer range isn't achievable for several other reasons anyways.

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