Re: [CAD_CAM_EDM_DRO] How does one adjust Ballscrews on a Bridgeport

Stephen Wille Padnos wrote:

>>
>>
>Yes - it does appear to move in the bracket. We put one heck of a
>preload on the end bearings - we used some Aluminum tube as a shim, and
>tightened the end nut *VERY* hard. We didn't want to go too far, since
>there are only 5 or 6 threads on the nut. Do you have some idea of the
>amount of torque these should have on them?
>

You actually should have 1000 Lbs or so of preload on the bearings, so they
don't "give" when the screw is pushing on them. That doesn't take a whole
lot of tightening on the nut, though. What "nut" is this? Are you sure
it is
really clamping the inner races of the bearings?

>
>
>
>>Are you sure you installed the bearing sets exactly as they came out of
>>the machine?
>>There's a plate that screws on over the outermost bearing that applies
>>the preload
>>to the outer races. But, something has to hold the inner races together
>>and tightly
>>to the screw. It looks like in the stock setup that is the graduated
>>dial hub.
>>Do you have a similar part on your ballscrew setup? If the screw can pull
>>inward until something else jams against the inner races, that might be
>>your problem.
>>
>>Jon
>>
>>
>>
>>
>Yes - the orientation of the bearings is the same relative to one
>another (even rotationally - there were marks :). I may have installed
>the set backwards, but I would think that wouldn't matter. Then again,
>I don't know what the problem is, so maybe I'll just go spin them around :)
>
>The stack on the end of the ballscrew is: nut - washer - handwheel -
>dial hub - bearings - screw shoulder. I just dis- and re-assembled that
>side, and put it back together without the dial so I could see what was
>happening. The dial hub is definitely pushing against the inner race of
>the bearing. There is a flange on the hub, but it doesn't hit the
>bearing retainer ring (which pinches the outer races together).
>
>I tried putting a dial indicator on the other side of the screw (the
>side with the single "floating" bearing), and I can see that the screw
>definitely moves relative to the table. This tells me that there isn't
>any backlash in the ballnut (or at least, it's not important yet).
>
>I think the next thing we try will be some shims either between the
>inner races of the two bearings, or between the outer races and the
>bearing housing.
>
>

I have the Bridgeport manual here, and looked to refresh my memory of the
mechanism. (I don't have a real maintenance manual, but it does have an
illustrated parts breakdown of the leadscrew brackets. I don't see any
shims
in there. But, it is pretty clear that if you have the inner races
clamped hard
together, then they have simply hit each other, and not given any preload.
IE, the inner races should have a gap between them, transferring force from
the inner races to the outer races, and pushing them together. This is
obviously
not happening.

Is there any possibility it was like this before? The Bridgeport M-105
manual
lists the bearings as Norma Hoffman XF-12 felt sealed ball bearings.
The cross
section drawing makes them look like they probably are angular contact,
with the
wider gap in the races facing outward from the bearing pair. If these
bearings
are just standard radial ball bearings, then the inner and outer races
will have
the same width, and no amount of pushing on the inner races will
actually preload
them. I'm just wondering if the bearings have been replaced incorrectly, or
with the wrong type.

Jon