pulley ratios : motor to ballscrew

[circlecn]

Hi, I purchased an IH mill from its previous owner a while ago and much of the hardware to convert it to cnc. I have been off on other things for a while but now want to get the conversion completed.

Here is what I have:

(1) Homeshopcnc 850 oz/in at 72 volts with 4200 rpm at constant voltage
(2) 3/4 5TPI Rockford Ball screws
(3) I have 72 volt power supply.

I am trying to decide on the pulley ratios I should use for each axis. I am not sure how to make this decision. I know that 4200rpm and a ratio of 4:1 I should see ~~210 inch/minute linear motion with these balls crews. How can one analyze this situation.

What rpm should I use for calculation and what linear speed should I be trying for? Should all the axis be the same? What other factors should I be considering?

Thanks for your help.

Kent

[circlecn]

Hi, Quite a few looks but no opinions.

Is there too little information to give an intelligent reply or is the question to dumb to bother with? I am going with 4:1 as that seems to be what most people do but I thought I would try and make a decision based on theory.

Just curious.

Kent

[Andre' B]

Not much time and I will not be back for a few days.

I would aim for a resolution of around 0.0001 to 0.000025, but I would be using EMC and a torque or velocity mode servo system rather then a position mode (step/direction) that seems to be so popular. With EMC and torque/velocity mode control you do not have to make as much of a compomise between resolution and speed because you are not limited to the max step rate of the software .

I would take a WAG and say a resolution less then 0.0001 is going to be pushing the limits of what your iron and parts can make use of.

[Runner4404spd]

i would use a pulley ratio of about 4:1