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

Stephen Wille Padnos wrote:

>Hi, all.
>
>Both myself and a friend are having the same issue with our Bridgeport
>milling machines. We're both converting manual machines to CNC. I
>installed new ballscrews (his machine came with ballscrews), and they
>feel "springy". If I lock the table and push the handwheel, it turns a
>little (around 8-10 mils, according to the dials). If I let go, it will
>spring back to where it started. It gets harder to push (like a
>spring), until eventually I overcome the table lock friction, and the
>table moves.
>
>

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.

>I'm using the same bearings that were used for the leadscrews I
>replaced. They are dual opposing Fafnir 204KT4 on one side, and a
>single SKF 6204 on the other side (the single bearing on my friend's
>machine is a Fafnir 204KTT).
>
>We're not quite sure how to proceed. We have thought of putting shims
>in various places - between the inner races of the two angle bearings or
>between the outer race and the bearing bracket. It seems like a preload
>problem, we're just not sure what needs to be preloaded.
>
>

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

>The odd thing is that I don't remember the leadscrew doing this (though
>it was one of the first things I pulled out of the machine for the
>retrofit :), and my friend is pretty sure his didn't do this when he
>bought it (the table had to be removed for shipping, so he did take his
>machine apart and put it back together).
>
>Any ideas?
>
>Thanks
>- Steve
>
>
>
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