how to convert a mill to cnc?

I have now reduced the backlash in my mill to 5 thou from 10, but dont know what an aceptable level is, so is this too much or will it do?

Thanks

The acceptable level is whatever you are prepared to accept :smile:

If the sloppy slide is tight enough to resist the cutting pressure you can then correct backlash with software.

thanks for info, the table should not move under cutting pressure so backlash compensation should help. been looking at the nema 34 kits from zapp and woundered if they were powerful enough but dont know what size motors i need

Hello Speedhound,
It looks like a nice machine .
And it will take a serious effort to make it run .
But nothing that a few hours in your workshop cant fix
Is it correct to assume you have changed the axis to ballscrews (there are zero backlash preloaded ballscrews).
If so which kind of bearings you use on the end (the rigid side).
You will need bearings that get rid of the radial and axial play.
you can do that whit one bearing ore a combination of more then one.
On the opposite side they need to be supported whit a needle bearing ore a ball bearing .
In a way they can compensate expansion and shrinkage of the ballscrew.
For the motor it will depend on how fast you want to go whit the feeds.
They have told me for a mill like yours you need about 8 NM on the screw
So if you have 3NM motor it need a reduction of 3 to accomplish your goal.
Enjoy your build.
Kind regards,
Andre.

Experience is the sum of stupidities you have done.

Dont forget a 3Nm motor will not give you 3Nm, unless it is at zero speed.
The 3Nm is holding torque and the actual torque you will get is dependant on the driver, RPM and Voltage.
You need to look at the torque curve of the motor to determine the torque.
as an example a 3nm holding torque motor will give you between 0.4Nm to 1.8Nm depending on the voltage and speed.

Thanks for replys, it doesnt have ballscrews which is why i was concerned about backlash but hopefully backlash compensation would help out with that. 8nm is interesting, this is the kind of thing i need to know as i dont know what motors to use. I understand that the motors are rated on holding torque. What size motors do you think i would get away with(would i need 12nm), i dont mind if its a bit slow but want it to be useable, so i could gear it down 2:1 or something but i dont know how fast it would be.

Thanks

Are you sure that leaving 1.5Nm of torque eating gunge in the slideway so that the table will hold position for your backlash correction is the best way to go? Surely it is eating the nut :eek:

I assume you will need a central lubrication system to keep everything running and then you will have possibly less then 1,5NM on the slideways .
If you set it at intervals of 20 min and lasting approximately 10 sec on each slideway.
Kind regards,
Andre.

Experience is the sum of stupidities you have done.

I dont think that it is gunge causing the 1.5nm of torque, its just a very heavy table, and that is the torque that is needed to get the table moving. Im not planning to use it loads, but keeping it well oiled like you say should help with the friction.

Thanks