Re: [CAD_CAM_EDM_DRO] Re: Gecko + Servos + Taig Mill

Dan Mauch wrote:

> One of the big reasons that makes a sherline/taig nice is the .050 pitch
> leadscrew. You get enormous mechanical advantage with the stock leadscrews.
> On the sherline mill I added a servo motor with 200 CPR encoder and
> directly coupled the motor shaft to the leadscrew. I measured the speed of
> the table at 72 IPM which is really to fast for a sherline. The reason I say
> that is because at 72 IPM the motor was running at 1440 RPM. The Sherline
> doesn't use radial bearing in their end plates however the motor that I plan
> to add to my products list will have ballbearings on the driven end. With
> direct drive I measured the axial force at over 25lbs.

You are saying the stall torque is 25 Lbs. force? Hmm, that seems pretty
light. I designed my servo system on my Bridgeport conversion for 1000 Lbs.
force. I probably do not get quite that, due to an accumulation of losses in
the chain of components, but I'm sure it gets close. I have broken off a 3/8"
endmill in the collet without even causing a fault. It DID knock the head out
of tram, though.

> At this force you would have deflection of the Z axis so cutting speeds
> would have to obviously be less unless cutting a very soft material.
> If there is interest I can take a picture of the sheline with the servo
> motor mount setup and email it off line to those interested.

Well, I'm sure I suffer many deflections in my machine before I get anywhere
near the full stall limit, but it will continue cutting under the heavy load.
I think 25 Lbs. Force is just awfully weak, and that you could easily
bog down on fairly normal cutting jobs. I know from my manual machining
days that I would often feel those levels of force when doing moderate
milling cuts.

Jon