Hey, all;

I'm working on an upgrade of the electronics on my Lagunmatic 250 CNC mill, and I'm adding an encoder (from a smaller 1 hp motor) to the 5 hp spindle motor, so I can do things like rigid tapping.

The mill head has a variable speed pulley with a V belt, in a similar mechanism to the bridgeport variable speed heads (or the Lagun FTV-2 mill, the manual for which is around on the net).

I'm wondering: How much backlash will the variable speed pulley system create? Will having the encoder on the spindle motor (instead of on the spindle itself) with the belts in between motor and spindle cause me severe accuracy problems?

I'm using a Hitachi WJ200 VFD, and the encoder is a differential quadrature type with 1024 cpr. I'm taking the encoder feedback into Linuxcnc, not into the VFD.

Anyone done something similar?

On a side note, since I removed the electromechanical brake on the spindle to fit the encoder, should I plan on replacing it with a magnetic brake or would the VFD's dynamic braking function do just as well?


Thanks,
Erik