How would this work??

[vidio1]

Like many here I'm slowly doing a CNC conversion. I've read through a ton of threads about quill vs knee for a Z axis. I had a brainstorm, or not LOL, and thought about using a powered feed like this: Power Feeds It's a prepackaged and actually designed to move a knee.
I'm assuming it's an induction motor and doesn't appear to have any feedback, so what sort of problems would I run into trying to control something like this? Has it been done before? Thanks for any input in advance...

[keebler303]

Your link doesn't work.
There is no feedback.
The motor is probably a "universal" type, I am not aware of any drive which can operate a universal motor in a ervo application. You could however replace the motor with a brushed dc type which could be easily servo controlled.

Matt

[vidio1]

I'm not sure why the link didn't work for you. It's a link to a Servo Products power feed, but that was just an example of what I had in mind. The type 200 feed from them is listed as a "half-wave series motor" another is listed as "full-wave SCR control compound DC motor".
Admittedly I don't full understand those terms, but I think they refer to DC motors being driven by an AC circuit. In which case they could be driven by a brushed DC type controller, or am I totally lost?
As for feedback. I would more about where or if there was room for an encoder once the unit was disassembled, but that's a moot if the drive can't be controlled without breaking the bank.

[keebler303]

The link is working now, maybe it was my work computer.

It sounds like either configuration uses a dc motor, th cheap one with just a diode in series with the motor and the more expensive one with the full wave control. If it is a normal dc motor, then you can use a normal servo drive on it after you fit an encoder. I don't have experience with these units so I don't know about backlash in the drive mechanism but I know that you shouldn't have any backlash in the actual knee due to the weight of it always keeping the nut push down on the threads.

Matt

[vidio1]

That's pretty much what I was thinking. I think that's the direction I'm going when I gwt to that part.

[79TigerPilot]

I see some issues; back lash, the difficulty in turning the motor into a servo and speed. The power feeds have failry low HP motors. The cost of converting the power feed would out way just making a knee feed.

On my J-head Bridgeport conversion I have both a quill feed and a knee feed. Both use steppers and timing belts. For the knee I added a timing pulley to the lead screw just below the bearing support up inside the knee. The belt runs through a small window cut in the side of the knee casting to the stepper mounted with a bracket on the outside of the knee. Initially I was was using the old acme screw but just finished an upgrade to a ball screw. Most of my cutting is done with the quill feed but almost all tool changes requre the knee to be adjusted. In the quill feed the stepper drives a ball screw using a 2:1 timing belt reduction. The ball nut is attached directly to the quill so there is no backlash like would come from driving the rack gear. I get 100 IPM on both quill and knee.

Craig

Originally Posted by vidio1 Like many here I'm slowly doing a CNC conversion. I've read through a ton of threads about quill vs knee for a Z axis. I had a brainstorm, or not LOL, and thought about using a powered feed like this: Power Feeds It's a prepackaged and actually designed to move a knee. I'm assuming it's an induction motor and doesn't appear to have any feedback, so what sort of problems would I run into trying to control something like this? Has it been done before? Thanks for any input in advance...

[vidio1]

@79tigerpilot I've seen you Z axis thread. Impressive stuff, I especially like the quill drive. I hope to do something similar. I have an Alliant mill that was converted on X and Y with Millport controls and a power feed on the knee. For the time being I'd like to convert the power feed to control and use it as a Z axis. As time and more importantly money permits I'll try to come up with a quill drive design......