ML7 : To convert, or not...

[JohnHaine]

I have cnc'd my Super 7 and I'm very glad I did. It's a late PXF version, which has room in the saddle for a 12mm ballscrew, though I had to mount the nut sticking out because there isn't room to mount it conventionally. The 12mm screw has enough rigidity that you don't need a bearing on the back.

For the non-PXF S7 and ML7 the hole in the cross slide is too small for a 12mm screw. If you look at this site:

https://cncyourmyford.com/

...he uses an 8mm ballscrew screw (I think) - these are more expensive and do need another thrust bearing at the back and to keep the screw under some tension. I think the same approach would work for the ML7.

My X ballscrew I think has a 2.5 or 3 mm pitch - whatever it is it's swallowed up in the axis setup in Mach 3. The 8mm screw will have a smaller pitch. I started driving the screw with timing belt and pulleys but went over to direct drive from the stepper when I fitted the ballscrew as I think I was getting cyclic errors from slight pulley eccentricities.

As for the Z screw - so far I haven't found a situation where I can't avoid having to cut in the positive direction, but at some point I would like to convert to a ballscrew. The above site explains how and he also sells some castings to adapt the apron. You need to keep chips off the screw, and he uses a very neat approach using Dyson vac hoses as bellows! I use Tony Jeffree's approach of a stepper on a bracket at the back of the lathe with timing belt drive to a pulley that replaces the Z handwheel. Of course the leadscrew is 1/8" pitch (on my "metric" lathe!) but again Mach 3 takes care of that.

I've done some other mods, mainly removing the flimsy Myford topslide and making a very solid toolpost mounting block for the Dickson toolholder which is dowelled so I can quickly change tools and maintain referencing. I haven't fitted limit switches, I can't see they are much use on the lathe, I do use soft limits in particular to avoid running the crossslide off the ballnut! I've fitted a crosslide reference "switch" that zeros Mach3 at the start of a session - once all my tools are calibrated I can just dial in the tool number and pretty reliably cut to a known diameter.

Happy to answer any further questions if I can help. I love CNC turning!

PS: The way I've done the conversion, I can put the lathe back to its standard state with no issues. In particular I made a new bracket for the cross-slide screw motor mount.