[mrsa]

I have a 2meters Z axis lathe (about 2tons machine) and i want to put a servo motor to move z axis. I don't want to use ballscrew because i need 32mm diameter 2+ meters ballscrew which is costly. What options exist for rack-pinion without backlash? Also servobelt is suitable for this case? What belt to use with servobelt?

[Jim Dawson]

Is this a manual lathe now?

[mrsa]

Yes is a manual lathe now that has in Z axis feed bar for feeds leadscrew for threads and rack pinion for hand moving. But all these have backlash.

[Jim Dawson]

If you put an air spring on the carriage it will cancel the backlash and you can drive the carriage with the feed bar. I was going to do this to my lathe and convert it to CNC but keep all of the manual capability, but I bought a CNC lathe and never converted the manual.

[mrsa]

spring is not a solution because i want z cutting from both sides left & right. What options exist for backlash free rack-pinion ? servobelt is ok for this application? What belt i need for servobelt?

[Jim Dawson]

An air spring will work if it is designed correctly. But you can use the existing rack and use double gears on it.

I would not use a belt for this application. I have used Gates HTD belts for similar positioning applications.

[mrsa]

What about 2005 ballscrew with rotating ballnut(not rotating ballscrew)?

[Jim Dawson]

That would work perfectly. Maybe also look at a 2010 ball screw

[hfjbuis]

I have converted my lathes for CNC turning but I can (and want/need) still use them manually. I use the original lead screws. That works OK (for me) because I do CNC turning the same way I do manual turning. It is just the computer that turns the dials. Backlash is compensated in software and I use a tool table so I can change from outer to inner turning without adjustments. I do facing, turning (taper), chamfer and threading without any problems. Even turning a gear cutter or timing belt pulley cutter is not a problem. The limitation is for complex forms where the tool has to move often in opposite directions like turning a chess peace. Also if every second counts, you better choose backlash free spindles, because backlash compensation cost time to execute.
I don't say it is the way to go for every one, but for me, who wants to keep the manual capabilities, is works OK.