Re: bridgeport - geckodrives and mach 2

Hey guys, I'm right smack at the beginning of a similar conversion
project. A bunch of friends helped move in a '79 Bridgeport CNC this
weekend. It came functional with a '98 AHHA CNC conversion using all
the original Textron (boss?) full-step stepper drivers.

I've no 3phase, or 220v power even. Just 110v - 35A max (can't let
two tools start up at the same time). To test the drives a friend
and I hacked into the AC power box, bypassed the 3phase transformer
and lit up the electronics and computer direct from 110.

To power the stepper drivers we used a separate torrid to step 110V
down to the specified ~55V and tied the three separate drive axis
power inputs together. We had first tried to use the BP's built in
220V to 110V Electronics transformer with some success but stopped
at the sight of smoke (transformer got a little hot).

This has us wondering how many amps the stock drivers pull. Anyone?

Performance was marginal in this configuration. I can't compare
before/after performance as I didn't play with the machine much on 3
phase. We started loosing steps when jogging the configured ~20ipm
rapid -- especially when retracting Z and at extreme X table
positions where the saddle supports a larger cantilevered load.

Late last night I puzzled out the motor wiring and hooked the X axis
(wired in series) up to another NC control box I had built for an
Enco conversion. It uses Centent 142 10x micro step drivers (an
earlier generation of the Geckos). Using another PC and Mach2 I had
the X axis jogging reliably at 80ipm. 90ipm appears to be the max.
I'll probably back it off more for safety.

The drives are powered at 40VDC and set to ~6.5A but I am unsure of
the actual stepper current--it's somehow dependant on how the motor
is wired. I understand Ohm's law but don't see how the driver knows
to deliver ~3.5A max when the motor coils are wired in parallel vs.
~7A max for series (seems counter-intuitive).

Les, or anyone else, do you know where to find the specs on the BP
stepper motors? (Superior Electric version)

Next is the spindle.
I plan to buy a Hitachi L100-015NFU VFD from Drives Warehouse. The
015NFU model takes 220VAC single phase. I've a few (large) 1:2
transformers and plan on stepping 110VAC up to 220VAC. But I believe
it is possible to bypass the drive's internal rectifier and just
feed it 220VDC. My assumption is that I might get better performance
if I externally rectify and filter the 220VAC to DC as the internal
DC filter cap is small and I suspect the cap is sized more
appropriately for 3-phase.

Anyone try anything like this?

Wish me luck! - Ted Griebling

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Les Newell <les@l...> wrote:
> Hi Aaron,
>
> I have converted my Series 1 BP to Geckos and Mach2. The machine
> performs far better than with the original BOSS5 control. Rapids
are
> about twice as fast and movement is much smoother.
>
> Geckos are slightly undersized for the Bridgeport steppers but
they work
> quite well if the motors are wired using only two coils and the
Geckos
> are run at full current and about 75V.
>
> Les
>
> Aaron wrote:
> > Has anyone converted a bridgeport mill using mach2 controlling
geck drive
> >
> > .....any comment oon this combo would be grately recieved
> >
> >
> >
> > thanx
> >
> > Aaron