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

Seems like we are comparing apples and oranges here. A Sherline is a tiny
machine and same with a Taig. A 3/8" mill is a big bit for these machines
and taking a .100" depth of cut is a lot (don't think I ever cut that much
in one pass when I had the Sherline). 25 lbs of cutting force would be a
huge amount for one of these machines and would almost definitely deflect
the vertical column significantly. If I remember the lead screws are only
1/4-20. How much force do you think they would take before deflecting when
you consider that you can have about 10" unsupported on the X axis if moved
all the way to the positive end?

Tim
[Denver, CO]

> 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
>
>
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