Re: [CAD_CAM_EDM_DRO] newbie Question

Marv Frankel wrote:

> Jon,
> I have an Enco Model #100-1525, that's about the same size and
> configuration as your Bridgeport, and I'm really interested in how easy or
> difficult it was. My mill has a 2-speed control, and if I choose to change
> the belt, Speed #1 is from 100 to 680 RPM, and Speed #2 is from 520 to 3500
> RPM. I seldom chage belts, because I also have a VFD controller. If it's not
> too much trouble, an explanation of the retrofit, and some pictures, would
> sure be appreciated by me, and I'm sure, a lot of other guys.

I have some pictures on my web pages, at http://pico-systems.com/CNCconv.html
which is mostly mechanical, and http://pico-systems.com/EMC.html which deals
more with the electrical part. This is a servo-controlled machine, as I have a
passionate dislike of steppers in precise positioning applications.

I was lucky enough to stumble across an Excellon PC board drilling machine
that was being scrapped. It had a hideous old GE Mark Century CNC control,
no computer, hundreds of small paper-phenolic PC boards with germanium
transistors, paper tape, I let them haul that to the dump. but, I got the 2
air-bearing drilling spindles, and the 2 main axes. these have high-precision
ballscrews, DC servo motors, and resolvers. I pulled the resolvers out and
installed encoders. I had to fabricate a "yoke" to hold the ball nuts, and it was
a massive chore. If I had to do it over again, I would make cylindrical adaptors
that would slide in where the original bronze nuts went into the original Bridgeport
yoke. I lost some Y axis travel with my own yoke. I could fix it, and probably will
at some time, because that would be easier than converting to use the Bridgeport
yoke, I think.

I made my own Z axis on the quill, using only a small ballscrew to start with.
I used a motor out of a computer tape drive, and another encoder. There's another
page on just the quill drive, with a link on the first page given above.
This was a near nightmare! The shape of the Bridgeport J head has lots of
curves, and is real hard to measure. I even made a rough cardboard template
to make sure everything would clear. The template looked fine. But, when I
assembled the finished unit, the encoder would need to be buried 1/2" inside the
belt housing! So, I had to mill big oval slots so the thing could be mounted about 3/4"
further out from the front of the main spindle housing. I hadn't cut the link between
the quill and the ballscrew yet, so i didn't have to hack that part, at least.
You can see in the 2nd picture of the Z-axis detail page how close the encoder is to
touching the head.

The electronic part of it was no biggie to me, as I'm an electrical engineer. I ended up
designing my own servo amps, which was an insane waste of time. It took me about a
whole year to go through that until I had a totally stable design.

I started with a hideous, old, Allen-Bradley CNC control, and used it for a while until
EMC came along to a point where it was usable.

Jon