# Are ball-screws required for a CNC lathe conversion?



## AndySomogyi (Dec 11, 2019)

I've got a Clausing 5400 that I want to convert to CNC, but still want to use in manual mode. Currently it has a 5/8x10 cross slide screw. I know one issue with ball screws is they have to be continuously held somehow, or else they'll back drive. So, would a regular 5/8-10 cross slide and brass nut work OK with a CNC, or would I be better off converting to ball screw, and coming up with some way to lock the screws in manual mode?


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## T Bredehoft (Dec 11, 2019)

I see no advantage to leaving the cross feed as a regular screw.  If it will be driven by CNC, then is should be a ball screw. CNC will hold it in place.


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## JimDawson (Dec 11, 2019)

I would use a ball screw on the cross slide.  Just snug up the gibs to keep it from back driving.  I don't have any problem on my mill when using it in manual mode.  Be sure to get a left hand thread ball screw else the cross slide will work backwards in manual mode.  A 5/8 -10 ball screw would be perfect, that way your dial is still accurate.

For the carriage, I would not use a ball screw at all.  Just use the rack & pinion to drive the carriage, and preload it with an air spring when operating in CNC mode.  That way you lose none of the manual functionality of the lathe.  For best accuracy, a linear scale feeding back to the controller would be the best solution.  I would put linear scales on both axes.


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## cjtoombs (Dec 11, 2019)

I think it depends on what control software you plan to use, you would need one with backlash compensation.  Lathe turning doesn't have the climb cutting issue that mills do, and generally you don't cut circles on a lathe.  If you are using Linux CNC you could use backlash compensation and plan your cuts around the backlash, which probably would only require thought on a rare basis.  I was thinking about doing this at one time and chatted with a fellow on another forum who had done it and they didn't have any real problems.  The acme screws will limit your rapid speeds, but for hobby use that's not much of an impediment.


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## AndySomogyi (Dec 11, 2019)

JimDawson said:


> I would use a ball screw on the cross slide. Just snug up the gibs to keep it from back driving. I don't have any problem on my mill when using it in manual mode. Be sure to get a left hand thread ball screw else the cross slide will work backwards in manual mode. A 5/8 -10 ball screw would be perfect, that way your dial is still accurate.
> 
> For the carriage, I would not use a ball screw at all. Just use the rack & pinion to drive the carriage, and preload it with an air spring when operating in CNC mode. That way you lose none of the manual functionality of the lathe. For best accuracy, a linear scale feeding back to the controller would be the best solution. I would put linear scales on both axes.



Most of the ball screw I’ve been able to find are M16x5, so that’s roughly twice as coarse as the 10 TPI ones I have. 

The first thing I’m doing is converting it to electronic lead screw, so I suppose I could adapt the controller software to act like a stepper motor, and get input from a serial port CNC commands and have it drive the gear / rack 


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## JimDawson (Dec 11, 2019)

Some research turned up nothing for a 5/8 x 0.1 ball screw, only 5/8 x 0.2



AndySomogyi said:


> The first thing I’m doing is converting it to electronic lead screw, so I suppose I could adapt the controller software to act like a stepper motor, and get input from a serial port CNC commands and have it drive the gear / rack



Not sure what you mean here.  I understand electronic lead screw, but not sure about the rest of it.


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## AndySomogyi (Dec 12, 2019)

JimDawson said:


> Some research turned up nothing for a 5/8 x 0.1 ball screw, only 5/8 x 0.2
> 
> 
> 
> Not sure what you mean here. I understand electronic lead screw, but not sure about the rest of it.



An electronic lead screw (ELS) is normally all self contained, it runs the screw at a relative amount to spindle angle.

But it should also be possible to add a serial port input to the ELS, and make the ELS act like a stepper motor. Basically augment the ELS controller to have a normal ELS mode and a stepper motor mode where it looks like a stepper motor. So, a CNC program would hook up to the ELS, but thinking it was a normal stepper motor. Effectively in stepper motor mode, the ELS would simply relay commands from the CNC forward to the stepper motor that’s hooked up to the lead screw. 



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## JimDawson (Dec 12, 2019)

Ahhh, I get it


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## coherent (Dec 12, 2019)

I've seen a number of conversions using the original acme screws. Will it be as accurate as precision screws? No. Will it work? yes. Many folks make the conversion with the original screws with the plan on upgrading to ball screws later. Most driver software allows for you to input backlash compensation for each axis. If it's really excessive your best option may be to just go ahead and replace it with ballscrews instead of messing with the original. Not sure what you mean by "held in place". The screw type has no effect on that... maybe gib adjustment, friction, lubrication or keeping your hand on the manual wheel? As far as CNC, when the steppers or servo motors are energized/powered, they lock in place and all movement is driver controlled via pendant or code. When no power is applied, they  free turn. Only caution when using a CNC axis in manual mode is that when you turn the crank/handle the motor generates power just like a generator does and can send back power to the driver board. Many breakout/driver boards compensate for this and can accept it, some may not and you can damage the board, so just something to be aware of.


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