Myford 7, 3 phase motor other CNC questions.

[JohnHaine]

Hi Joe, I've converted my Super 7 to CNC with a ballscrew on the cross slide so far. These two pics show the fitting. I made a new bracket to fit on the end of the Xslide as I wanted to be able to convert the lathe back, so not start hacking any Myford bits. I think the PXF S7 is easier because the normal feedscrew is larger than the standard ML7 or non-PXF S7, so there is quite a large "tunnel" through the slide body which will pass a 12mm x 5mm pitch ballscrew (from Arc). In order to mount the nut I milled up an ali block which you can see at the back of the nut - this is first screwed onto the saddle using the normal feednut mounting holes, then the flange of the ballnut is bolted to it. This was an interesting job for my little CNC mill. What you can't see is that on the back of the block is a spigot to locate it in the feedscrew tunnel. As I'm using a 12 mm screw I think I can get away without a support bearing on the other end. At the drive end the screw is turned down to 8mm, it's direct driven from the motor through an Oldham coupling, and runs in a needle roller bearing in the end plate with a couple of roller thrust bearings either side of the plate.

I'm using the standard leadscrew at the moment, with the stepper bolted to a 6mm ali plate in turn bolted on another 12 mm plate that picks up the row of machined holes along the back of the bed. There are slots to allow for belt tensioning. The stepper drives the leadscrew through a 1:2 toothed belt. It's crude but effective! I generally followed Tony Jeffree's conversion on the leadscrew but didn't bother with boring out the hole in the bearing, just fitted roller thrust races which self-align quite happily.


There was a chap exhibiting at the Midlands exhibition who had a very nice conversion of a non-PXF S7, and I believe he is planning to make a kit available. You can see it on YouTube at cncyourmyford, and his email is cncyourmyford [at] btinternet.com. He does a proper job on the cross slide with bearings at both ends of the screw but has to use an 8mm ballscrew since the non-PXF slide has a smaller hole through it. He also fits a ballscrew in place of the leadscrew, by dropping off the Apron and fitting a new one from an alloy casting. I am thinking of doing something similar but fabricating a new apron.