Bridgeport X & Y feed screw nut replacement ...

FOMOGO

FOMOGO

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Tearing into my B-port and trying figure a few things out. While I enjoy the work, I have a ton of other projects to do and would like to have it operational sooner than later. I've looked at parts, and for under $250 I can replace both feed nuts and the cross feed screw. Most of the end play is in the Y axis. In the parts break down they show both one and two piece nuts. I checked past threads and found some info, but would like to know from those who have been there which is best, and why. There was also mention of a two piece nut with a spring used on a lathe, which remembering after I removed the nuts from the casting, led me over to my collection of misc. springs. Low and behold, there was one just the right diameter and length that in my tiny mind seemed just right for the job. My thinking is, get the two piece nut for the X axis and install them with the spring in-between to maintain Zero backlash everywhere on the length of the screw regardless of regional wear. I realize one of the nuts would have to be lapped to allow a slip fit, and both would have to be shortened some. Does this sound at all workable? Would it cause premature wear, or affect machining operations in any way? Just throwing it out there to see what those more experienced than I might think. Thanks, Mike

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MIke,

A shim might work but a spring would allow for some free play I think. On my clone mill, there is a screw on the nut that allows one to compress
the nut and pull it together slightly. I don't know how much play this will take up but I remember adjusting it twice so far since it was new 20 yrs. ago. It has a lot of use so it wouldn't surprise me that it will need to be replaced eventually. Maybe talk around a bit and see if an adjustable nut
can be had. My mill is an ENCO 9x42, now taken over by MSC.
 
They do split those nuts and add a cap screw adjustment to take up backlash. If you're set on replacing, I'd go with a ball bearing leadscrew, though they are pretty pricey.
 
Ball screws are required with a CNC mill. While CNC control is on the servo or stepper holds the screws tight all the time.

In manual though the ball screws will move (creep) when not intended. The original acme screw has more hold on the non moving axis. So if you have ball screws you need to always tighten down the non moving axis. For manual use not a good idea.
 
I bought the "Bridgeport Rebuild Manual", and the recommendation in there on the cross feed nuts is to actually cut them in half where the split is. Face them off in your lathe. re-install them with a heavy felt spacer between them. The felt allows oil to wick in for lubrication. This gives a significant amount of adjustment to take up backlash. I have not done this yet, but plan on using this technique. this approach is what the book terms "upgrade" in design. Again, I have not quite yet gotten to this point, but I plan on using the approach.
 
I split the nut on my x-axis feed and reduced the backlash from .097 to .007. My lead screw has very little wear getting only .002 tighter at the ends verses the center. Not difficult to do at all.
 
MBuechle said:
I split the nut on my x-axis feed and reduced the backlash from .097 to .007. My lead screw has very little wear getting only .002 tighter at the ends verses the center. Not difficult to do at all.
Click to expand...

Mine has .070 with everything tight. lol I'll be making replacements soon!
 
Expressline99, replace or modify? The modification makes sense, and is relatively easy to do.
 
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