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

Jon Elson wrote:

>Well, the first thing is to find out whether the leadscrew is moving in
>the bracket
>that is supposed to constrain it. If the steps on the end of the
>leadscrew were
>not made right, it may not be taking up all the play in the end
>bearings, which
>are supposed to be preloaded against each other.
>
>

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?

>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.

Thanks for the info.
- Steve