Ballscrews - Speed and Acceleration or how not to beat your ballscrews to death

[slow-poke]

My past CNC conversions used stepper motors so were inherently slow.

My latest conversion (8x30 Knee mill) with DFU2005 and DFU1605 ballscrews uses 750W ac servos, These are a world different in terms of torque at speed and I can move the table near silently (compared to steppers) and fast, test run at 100IPM is no problem.

I would imagine the forces at the ballscrews are not trivial. So my question is if I want longevity what are good limits to place on acceleration and velocity?

 

[RJSakowski]

My Tormach PCNC 700 series 3 uses 500 oz-in. (3.5 N-m) steppers with 5mm ball screws and has a specified rapid of 135 ipm. I have no idea what the maximum acceleration is set at.

 

[JimDawson]

My past CNC conversions used stepper motors so were inherently slow.

My latest conversion (8x30 Knee mill) with DFU2005 and DFU1605 ballscrews uses 750W ac servos, These are a world different in terms of torque at speed and I can move the table near silently (compared to steppers) and fast, test run at 100IPM is no problem.

I would imagine the forces at the ballscrews are not trivial. So my question is if I want longevity what are good limits to place on acceleration and velocity?

The machine should run quickly and smoothly. 100 IPM is a great number for rapids on a knee mill. Just adjust your acceleration until it gets jerky, then back it off until it's smooth. This is kind of subjective, but it works well. It also depends on your software and what control you have over the acceleration depending on the operating mode.

 

[slow-poke]

The machine should run quickly and smoothly. 100 IPM is a great number for rapids on a knee mill. Just adjust your acceleration until it gets jerky, then back it off until it's smooth. This is kind of subjective, but it works well. It also depends on your software and what control you have over the acceleration depending on the operating mode.

Thanks, that's helpful.

At the moment the servo control is setup for positioning based on the servo encoder, it actually seems quite accurate < 0.001" Longer term plan is to have the servos (inner loop) be velocity control and use the magnetic scales for the outer loop position control (I'm using LinuxCNC)