Re: [CAD_CAM_EDM_DRO] bridgeport ballscrew question

cnc_4_me wrote:

>have any of you that have converted a bridgeport to cnc, bought
>seperate ballscrews and nuts and made your own yoke...and machined
>the ballscew ends yourself...
>
>If so how sucessful were you...
>
>

Yup! been there, done that, and it was a BIG PAIN! I felt that the
origina;
Bridgeport yoke was not rigid enough, and made my own from a block
of steel. I had ballnuts that bolted to flat surfaces. Well, I lost 2
inches
of Y travel. I still don't know where the interference is, exactly, but
someday I
have to tear it apart and cut someplace on my yoke to get that travel back.
I really miss it! I only got about 9" on the original machine (old
round-ram
turret mill with the smaller knee) and mow I'm down to 7"! UGH!

Also, there's all sorts of shims all over the place to get the screws to run
parallel to axis travel. I measured EVERYTHING on a surface plate, with
dowel pins in the holes and a height gauge. but, it sure didn't COME OUT
right. I guess I've got some .040" of misalignment without the shims.

So, it works, and works quite well. I got the axis drive system out of an
Excellon PC board drilling machine. This had motors, belt reduction, paired
angular contact bearings, and resolvers. I replaced the resolvers with
encoders
directly driven by the end of the ballscrew, using helical-slitted
couplings.
The ballscrews are high precision grade ground screws, and probably cost
$5000 each! They had compensator cams on them, but I don't even have
tools accurate enough to measure the error in the screws as they are!
I used the biggest stack of gauge blocks I could assemble to check it
over about
a foot, and it was within .0002" or so, which was within the error I
could expect
from that big a stack of gauge blocks and my indicator.

But, if you don't want to spend a great deal of time aligning the whole
monstrosity,
this may not be the best way to go!

Jon