Re: Re: Sherline retrofit for CNC

Mario,

I've done several Sherlines. Two keys to accuracy are adjusting the
backlash out of the screw and eliminating end play in the stepper motor.
Sherline now sells CNC ready machines and they have a really nice
looking cast bracket that houses bearings that can be adjusted to
eliminate end play. It's much cleaner looking than making thrust plates
from flat stock like I've done. I'm sure Sherline sells these, you will
just need to get someone to drill and tap the mounting holes in the
appropriate locations.
All the Sherlines I've done, and my MAX, use 16 pitch precision rolled
acme stock. On the sherline, there isn't enough room to use antibacklash
nuts without heavy mods, so I used bronze nuts at both ends. These were
about 1/2 dia and I stepped them to 3/8, then machined the flange to
create flats 3/8 apart. The saddle was machined to accept these. One
side is bolted tight, the other is adjustable. I used VibraTite on the
adjustment screws. It is possible to get backlash down to .0005 if the
screw is accurate enough, but I got one length that had enough variation
I could do no better than .0015. I ended up using polymer antibacklash
nuts on my MAX as I had the room to mount them.
If you stay with the Sherline nuts, be prepared to adjust them
frequently! Also, consider spending some money for ground 1/4-20 thread
stock. No, I don't know where to get any off hand, but if you can find a
thread grinding shop doing a run, you might be able to talk them into
running an extra length for you.
I've held tolerances of +/-.001, though this was on plastics, not metal.

Jon

MIADsgns@... wrote:

>
> From: MIADsgns@...
>
> Hi Folks:
>
> I am looking to retrofit my sherline mils and lathe with stepper motors for
> making CNC miniature aluminum molds.
>
> I need them to be precise so can someone reccommend a retrofit kit for such?
>
> Has anyone retrofitted their Sherline for CNC what type of precicion can be
> expected?
>
> Thanks
> Mario
>
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