Thread: CNC Spindles on Ebay

Hi Chris
Nobody has responded so you get the electronics challenged reply.
You obviously need to feed at a given rate for threading. As I understand it there are three ways of doing it.
A 3 phase with VFD or a DC motor with variable speed. Both of these methods use a tachometer to monitor the speed and this feeds back to the controller to maintain a constant feed. A lot of guys use a treadmill motor so keep you eyes out on verge pickups.
The other way is to do what I am doing and use a servo motor and controller which has an encoder on the back of the motor to monitor the speed. The added advantage of the servo is it also know what degree the motor is at so you can start doing indexing as well.
Chances are I could be totally wrong about this but it is there to be corrected.

The lathes that were threading that I watched used an encoder on the spindle, an encoder with an index pulse.

This pulse is sent to the controller and it does the rest. It sets up the threading pass then starts motion at the same time every time according to the index pulse, but taking a deeper cut every time. It is quite amazing how accurate it is from just the index pulse.

The last one I was watching was a retrofit on a big lathe a mate did to thread 20mm reo bar for a customer. It had a bar feed that made it all a bit cooler, it came in, the tool smoothed out the bar first then started the thread, serious stuff. All very fast.

Russell.

Is it necessary to ground the spindle itself? (I'll be running the 2.2 KW , 400 HZ, 8 amp 220V spindle from Chinese Ebay vendor, running this with a Hitachi SJ200-015NFU VFD with single phase 220 input.) If so, where on the spindle do I attach the ground wire to? Should this ground wire (if required) be one of the conducters in the shielded cable, or a seperate bare or insulated wire? Thanks! Al Ladd www.alladd.com