Bridgeport Ballscrew Backlash- Test data

I think Ron hit the nail right on the head.
The tighter ways on the ends of travel cause
the extra backlash. But I think the ballscrews
are actually worn MORE on the ends than in
the center. I speculate that this is the
result of the machine being operated with
the gib snugged at the center of the table
and extra pressure being put on the ballscrews
at the ends of travel. This seems to make
sense to me.

Some test data:

Y-Axis:
.003" ballscrew endplay with gib snugged
.0007" ballscrew endplay with gib loose
.001" backlash measured at table with gib loose
.005" backlash measured at table with gib snugged

X-Axis:
.0025" ballscrew endplay with gib loose
.006" ballscrew endplay with gib snugged
.0065" backlash measured at table with gib loose
.011" backlash measured at table with gib snugged

You can see that a snugged gib really increases the ballscrew
endplay. I would assume that I do NOT need to replace the
bearings. Just do whatever to increase the preload on them?
Factor out the endplay, and at least the X axis ballscrew
would have a lot of backlash.

When I say the gib is "snugged", it is tightened to reduce
the table rocking, but not to the point that I really have
to put hard pressure on the gib screw to turn it. With the
gib "snugged", I fail to meet Bridgeport's standards of
.0005" of table rock. My table rock is more like .002".
When I say loose gib, I really mean loose.

So what do I do?

What kind of backlash should I expect?

I debated rescraping the X and Y axis on this machine but
decided against it because the ways really did not look
all that bad compared to a lot of other machines I have
seen.

It almost seems that a rescrape and ballscrew rebuild would
be in order. I actually had New England Machine Tool Rebuilders
quote me on a rescrape of just the X and Y axis last year.
Their price of $1500 I thought was very reasonable. I would
have to pay practically double that to have the ways rechromed
again. Their company consists of former Bridgeport employees.
I, as most, would rather go the least expensive route. I have
so much invested in this machine at this point that I need to
do whatever to get it running properly.

UGGGGGGG!!!!!!!


Scott