Myford Super 7 Lathe CNC Conversion anyone?

racedirector wrote:

So I have disassembled the apron and cross slide only to find that the cross slide has stuff all room for a ballscrew.

This is a common problem.
I used to have photos on cnczone of how I got round that with my mini-lathe, but they disappeared when they pulled the plug on Picasa.
However, thinking about it, it might not be that relevant anyway, as the mini-lathe has the nut on the cross-slide, and the Myford has it on the saddle.

I used a very small pulley (barely bigger then the screw) and T2.5 belt to turn the screw, with a needle-roller to take the belt tension. I then moved the thrust bearings towards the user, mounting them in a housing that replaced the handwheel bracket (I kept the handwheel). Moving the thrust bearings out of the way was a big help in making stuff fit.

It is possible that a rotating-nut arrangement might help. As the Myford moves the screw and not the nut, this might make getting the drive in easier. But I suspect that there basically isn't room.

Depending on how much space there is between the lathe and the wall, I think I would be looking to mount the motor round the back, driving the end of an extended screw with a belt drive. T2.5 and T5 belts have effectively zero backlash, and let you wrap the drive round itself for compactness. Even if you don't do this, a belt drive will take up less axial space than couplings.
whether you but the thrust bearings in the front side or back side would be a matter of taste. I think I would use the front side, where the handle is, but I don't have a Myford to look at to decide.

The best nut-diameter to screw-diameter ratio seems to be the RSH1605 nut, which is 1" diamter and takes a 16mm screw. However it has a surprise, there is an external ball return tube not shown in the catalogue.
Here is how I got round that with my mill

I used the same nut on my lathe, but have more space than you.

The only nut that will fit down the existing hole in the saddle is for a 6mm screw, and that probably isn't worth considering.
However, my Mini lathe ran for years with an 8mm ballscrew and it never gave any trouble. So you could consider that.
(When I say "Mini Lathe" it was a 9 x 30 lathe, about the same size machine as a long-bed Myford, but made with half the metal)

How much space do you have between the centre of the saddle hole and the underside of the cross-slide?

The right answer might be a complete new saddle casting, with space for a ballscrew and built-in mounts for the Z-nut. With the Myford bed design this isn't beyond the realms of possibility (It would be rather more of a challenge with an inverted-V bed)

rodw wrote:

Seeing you have a lathe, this is an easy and sturdy way to mount a stepper

And this is a not-easy but much-shorter way to do the same thing (seeing as I was on CNC zone looking for other old pictures)
www.cnczone.com/forums/uncategorised-met...ines/172314-cnc.html

(The machining in the video was done with the lathe with the 8mm cross-slide screw, to keep it relevant to this thread)