[bradyfb]

I HAVE 850 oz/inch servo motor Im want to drive the bridge on my cnc router with. And would like to know if there is a formula to tell me how big of ballscrew I can use: For example: 1 inch or 1.25 inch diameter at 60 inches long, plus the weight of the bridge, will this burn up the 850 oz/inch torque servomotor....? Need formula

[DennisCNC]

Look in the linear motion forum for my post.

You might what to drive the nut and not the entire screw if you need good accel and deccel. That will be a heavy chunk of metal to spin

[bradyfb]

Dennis, I'am new to this cnc stuff; and may not be asking this question the right way. the nut will be mounted to the bridge or gantry, which the ballscrew will be turning inside the nut. the screw will be mounted to the motor by a belt drive. and I'am sure that there is a limit to what diameter screw i can use with my 850 oz/inch torque servo motor before I risk burning the motor up, because I'm trying to turn to much weight/load... I do think that I have big motors or am I wrong?

[Evodyne]

Dennis, I'am new to this cnc stuff; and may not be asking this question the right way. the nut will be mounted to the bridge or gantry, which the ballscrew will be turning inside the nut. the screw will be mounted to the motor by a belt drive. and I'am sure that there is a limit to what diameter screw i can use with my 850 oz/inch torque servo motor before I risk burning the motor up, because I'm trying to turn to much weight/load... I do think that I have big motors or am I wrong?

Hi. Your 850 oz-in motors are not tiny by any means. And your belt and pulley arrangement between the motor and screw will work to your advantage: you will likely have a speed reduction of 3:1, 4:1, or more. If you reduce the motor speed at the screw by a factor N you boost the torque at the screw by the same amount. For example, a 4:1 reduction would make the screw think it was being driven by a 4 x 850 or 3400 oz-in motor. Plenty strong!

More important than the screw diameter is the threads-per-inch or lead. That will determine how much of the load (gantry, etc) is "seen" by the motor. I've got two 1" and two 1.125" diameter screws, all over 60" long and all having 5 threads per inch-a 1000 oz-in stepping motor directly coupled has no problem spinning any of them. I haven't done any testing to see how hard it can push the nut, but I'd guess it could handle any reasonable gantry without breaking a sweat.

Look at Roton's site for more information with respect to screws.

Good luck!

[Stevie]

Dennis, I'am new to this cnc stuff; and may not be asking this question the right way. the nut will be mounted to the bridge or gantry, which the ballscrew will be turning inside the nut. the screw will be mounted to the motor by a belt drive. and I'am sure that there is a limit to what diameter screw i can use with my 850 oz/inch torque servo motor before I risk burning the motor up, because I'm trying to turn to much weight/load... I do think that I have big motors or am I wrong?

I have 300 oz/in steppers on my new lathe witha 6-1 belt drive thats 1800oz/in
It ripped the treads out of the mounting plate when I missed a - sign from a test move; so 850 with a reduction would be plenty I'd say