Re: Bridgeport retrofit servo questions 1:1 ratio

Ron,
FYI, this is a BOSS machine. It was designed 100% for CNC with no
other purpose ~ according to Bridgeport specs. It is not a manual
mill converted to CNC.

The knee is manual to accomodate variations in material height. The
knee is not driven by the stepper. Only the quill/spindle shaft moves
in Z ~ quite a big difference in mass to move. The Z motor moves just
as easily as the X & Y ones, by hand turning a small 2.5" pulley with
my fingers.

To those of you that are going to try moving the pulleys by hand, do
so with the controls/power OFF. 1st reason being that quick movement
can acutally turn the motor into a generator and smoke the
driver...2nd and more importantly, a stepper has max holding torque
at zero RPM...once you break the magnetic lock on the motor and your
fingers are in there...It WILL BITE YOU!!! Don't ask how I know!
(Actually I knew this before hand in theory...but forgot) :)

-Brady




--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

>
>
> braidmeister <braidmeister@y...> wrote:
>
>
> Ron,
> I get what you are saying about 4th gear. I will try them 1:1 1st,
> and if need be, I will reduce to a 2:1 or better ratio. No sense in
> spending the $ for pulleys and belts if it is not necessary.
>
> In all actuality, yes it is a 3100 RPM servo @ 130 vdc. Since I am
> planning on running them @ 75v max, then I will have a max RPM of
> only about 1700. That brings the rapids down quite a bit. I doubt
> that I will need the full 2HP of the motor since I can easily move
> the axes by hand turning the pulley.
>
> /// We discussed the power input at the screw just recently. A

handcrank has about a 6" diameter path of travel, 3" radius. A crank
revolved 1 rev constitutes about 18.84 " of circular travel. This
circular distance produces .200" inches of linear table travel (5
tpi). Or 94.2:1 ratio. Each pound of force presented to the handle of
the crank equals 94.2 lbs of linear force. 10 lbs , roughly 1/2 ton.
So, servo torque is really not that big of an issue. The little
Ameteks will work for X and Y. Except in the case of Z driving the
knee. Different situation altogether. About 800lbs going up, coming
down is no problem. And then add a large bit hogging out material...Z
is the biggest headache by far. Put the biggest motor you can power
on it. I only get 50 ipm out of Z with a 40 in-lb motor. ///

>
> bounce things back and forth on...to me it is 100% American ~

Better,

> cheaper, faster
>
> /// As I told an engineer recently about those attributes, pick

two, ya can't have all three.///Ron

>
> & elimination of the middleman for those of us who
> know how to turn a wrench.
>
> -Brady
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
> wrote:
> >
> >
> > braidmeister
> wrote:
> >
> >
> > No I was the one throwing planes!!
> >
> > Yes, that's the motor in question. It seems to me that it would

be

> an
> > ideal fit for the BP. I am hoping that I can get away with 1:1

and

> a
> > decent encoder.
> >
> > /// Trying to run a 3100 rpm servo 1:1 to a 5 tpi ballscrew will
> produce rapids of 620 ipm. One needs from 2:1 to 3:1 reduction on

all

> 3 axies using servos (driving the knee, its half the increment of X
> and Y per rev.). Simply increasing encoder count to attain

resolution

> is not practical. An E5S-200 encoder, Gecko 320's and Mach2 work
> perfectly together using the above ratios. 1:1 ratio is like

driving

> a car around in 4th gear. Servos operate best at 80% of their rated
> RPM. I just ordered a set of pullies from mcmaster carr three L

(.375

> pitch)series 30 tooth (3.5" dia) and three L series 12 tooth ( 1.4"
> dia) for a 2.5:1 setup/// Ron
> >
> >
> >
> > [Non-text portions of this message have been removed]
>
>
>
>
>
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