Fehlmann Picomax 50 CNC conversion/refurb

[Robin Hewitt]

There's a build log from many years ago, I will try and link it...
http://www.mycncuk.com/threads/651-W...ht=Warco+Major
I fitted zero backlash double nuts, big disappointment, so I sprung them and it was like magic.
The springs mean that I have no backlash up to 1/4 ton but if I ever pass that loading presumably everything will go horribly wrong.
I do get some sideways slop in the quill if I forget to pack it out with thick, icky grease. Open to suggestions.

[Agathon]

There's a build log from many years ago, I will try and link it...
http://www.mycncuk.com/threads/651-W...ht=Warco+Major
I fitted zero backlash double nuts, big disappointment, so I sprung them and it was like magic.
The springs mean that I have no backlash up to 1/4 ton but if I ever pass that loading presumably everything will go horribly wrong.
I do get some sideways slop in the quill if I forget to pack it out with thick, icky grease. Open to suggestions.

I might give the belleville washer thing a go. The Fehlmann's vernier adjustment is clever, but I think a grub screw lock would be better as it would allow finer adjustment. Quality manufacturers have a nice trick of fitting a pressed-in brass plug in the adjustment nut before threading it so that you have a formed locking piece that doesn't damage the thread and needs little pressure to lock.

Regarding your quill slop, there isn't really a satisfactory solution. The fit of a cylinder into a bore is something that requires a degree of precision and careful fitting at the point of manufacture - surface finish is critical. Any fool with a cylindrical grinder and enough patience can make a cylinder to size and parallel to a micron or two, but getting the bore honed for a perfect transition fit is another issue altogether. Most of the Chinese machines fall at this point, although I have to say that Myford's VMC (Taiwanese) had a pretty decent fitting quill - though not to Swiss, German or the best US and GB standards (has to be said though that most of the machine tools produced in the UK were not of a particularly outstanding fit in this respect).

You could split the casting and put a clamp in place, but this is a pretty crappy solution as you're going to get lots of point contact at the clamp position (the bore will be an oval) and you'll still have the original clearance further up. Alternatively you could get the quill hard-chromed and ground to a nominal size slightly larger than the clearance, but then you have the difficult honing issue mentioned above. Not worth doing either of these, better to start again with a higher-grade machine and transfer your clever CNC additions to it.

If you've got space there's been some fantastic 1980s CNC machines on eBay recently including a couple of Deckel FP3/4s for about £1500! Fab things with superb ball-screws and servos (probably old brush types though).