"rotating nut" gearing question

[soren_dc]

Hi there.
I am currently building a modified version of joe´s machine and have been playing aroung with the idea of using a rotating nut setup for the x and y axis.

So i was hoping someone could tell me what gearing ratio would be suitable.

The lead screws are 12mm x 3mm pitch (in us around 1\2"-8tpi). And i will be using a 425oz\in kit from xylotex.

I don´t know what i am to expect in terms of speed and torque. But i was hoping to cut at minimum 60 ipm. Mostly guitar building and signs

Thanks.

[joecnc2006]

gear one to one on an acme rod, gearing down will decrease your speed tremindously.

you usually only gear down when using rack and pinion.

[soren_dc]

thanks for youre quick response joe.
And thanks for youre great work on the plans.

Of course youre right on that one.
But i was actually considering gearing the rotating nut up.
Because i see a lot of you guys are using higher pitched leadscrews like 4tpi or higher. and as i understand the 425oz\in motors would loose a lot of strength at the higher rpm´s needed to get the same speeds from a 8tpi leadscrew.

So by gearing the nut up and keeping the motor rpm´s down using timing belts and pulleys i am assuming i should be able to get what ever (tpi) i want.

So i was hoping someone could tell me what gearing ratio would be suitable
(The sweet spot). if there is such a thing

Hope you see what i mean. My english was never that good

[BobF]

Soren,
my machine uses 1/2 8 2 start which gives effective tpi of 4. I think Joe said he used 1/2 10 5 start on the 4/4. So something in that range is proven.