Re: bridgeport ballscrew question

WOW, that sounded like a big job...And that explains why the yokes
are castings and so funny looking (to complicated to machine all
those clearances needed out of a block)....

If i were to attempt to make one, i would try it in aluminum...Much
easier to hack clearance in were you need it...Steel must have been a
killer.

Arn't there any drawings of this stuff floating around...


Wally


Thinking about this a little more, i think the only purpose of the
yoke is to support the Y screw since it has no bearing mount on the
rear end....The yoke stops the Y shaft from wiggling off center...

I think it also provides a false sence of security on the X axis,
since when the table is all the way over the yoke isn't at the middle
of the X screw...And the X screw has bearings at both ends anyway...

I guess what i am getting at, is that a aluminum yoke should work
fine...At least acording to my arm chair engineering...


Wally

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> 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