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

Stephen Wille Padnos <spadnos@...> 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.

/// Which would tell me there is no backlash, if there were it would not return to where it started. If it does that in both directions with table locked. As Jon mentioned they are very low resistance which means the application of axial force converting to linear force is much easier than acme threads. Applying enough force to overcome the table lock is alot and an ample amount to break endmills. Thinking about it like this, considerably more linear force to the table can be created with a lower resistance ballscrew for the same amount of axial force applied to an acme thread leadscrew.////

It gets harder to push (like a
spring), until eventually I overcome the table lock friction, and the
table moves.

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.

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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