Ok, I decided to convert the mill to CNC to speed up a few time consuming processes, and probably gain accuracy. Â I'm planning to make a 4 axis conversion so I can machine the jet diffuser on it. Â I did consider 5 axis, but there's no really need right now, and the conversion of design into tool paths looks way more difficult, and the software vastly more expensive.
So my plan is to replace all the acme threads with ball screws. Â They're on order from china. Â C7 accuracy, so not earth shatteringly expensive and reasonably accurate. Â I've seen conversions using 16mm X and Y and 20mm Z. Â There's a lot narrower than the existing threads, so I've gone for 25mm and 32mm. Â Probably overkill, but I'd rather it that way around than waste all the cost and effort under-specifying. Â I'll then have Nema 34 motors (1600oz) mounted directly to the ballscrews on DIY built mounting blocks. Â On the Z axis I'll have a Nema 42 4100oz, which is probably double what's needed. Â I didn't see too much choice on (cheap) Nema 42 motors so pipped for this one as it was a reasonably cost, and the driver was the same as smaller ones anyway. Â I also got a 20:1 gearbox for the Z stepper for 99p off ebay. Â I might play with the gearbox and different step sizes to see what gives the best results. Â I don't need it, but for 99p it's nice to have the option.
The controller is a 5 axis job from ebay, and today I played with getting one axis wired up: