metric thread pitch to SAE question

[Setlab]

I have a 2.5mm pitch ballscrew and I need to set up the overall turns ratio in the wizard. How do I set up a units equation to convert a metric screw pitch to one in inches?

I have a 20 tooth gear on my motor belted to a 50 tooth gear on my ballscrew. That gives me a 2.5:1 gear ratio (50/20). So my initial overall turn ratio should be 2.5*ballscrew pitch.... I did some incorrect assumptions and made the ballscrew pitch just a simple mm to inch conversion (2.5mm = 0.0984252in) but that gave me a pully reduction ratio of 0.25 and some change which is extremely low. My mill axis doesn't even noticeably move with that input. I know there is the measurement method to get the overall turns ratio but I'm still on page 53 of the setup manual getting my initial numbers roughed out.

[Gary Campbell]

25.4 / 2.5 = 10.16 * 2.5 = 25.4
(mm per inch) / (metric pitch) = (ballscrew turns per inch) * (screw pulley) / (motor pulley) = (turns per inch)

2.5 seems awful fine for a ballscrew. Are you sure?

[Setlab]

Thank you! Now that I see it I feel a little dumb for not initially knowing how to do the conversion lol. I guess I'm not 100% positive it's a 2.5mm pitch ballscrew, the companies out of business and I got that info from a very knowlegble ex-employee. Now that you have me questioning it I'll measure a rough estimate tomorrow to see if its close.

[cnckeith]

turn the screw one revolution and measure how far the axis moves.
what type of machine is this on?
common milling machine metric pitches are 5 and 10
router 20 for XY and 5 for Z

related reading.
https://centroidcncforum.com/viewtopic.php?f=63&t=1801

and please always post a fresh report.zip when requesting support.