Bridgeport cross slide screw

[Paul Gauthier]

Today I removed the cross slide screw from my Bridgeport. This machine is a Line-A-Mill and has an optical tracer. The screws are ballscrews. Getting the screw out was not that bad an ordeal except for the last bolt, 1/4-20x3/4 socket head cap screw. Because of its location it took more that 1 hour to remove this bolt.
I had it out once before when I bought the machine about 12 or more years ago. Problem: excessive backlash as the screw and the balls were badly worn. At that time I replaced the balls and that helped some. Now it is beyond repair but I don't wish to shell out the $600.00 or more that a new screw with nuts would cost.
After removing the screw and cleaning it up I put in my lathe between centers so I could inspect it thoroughly. I could be wrong about this next part but I don't think so. I believe the screw is an ordinary Acme thread, 4 thds. to the inch,
with a couple of ball nuts on it. Inspecting each end of the screw where there is little to no wear, it is very clealy an acme. The thread is deep, way deeper than a ballscrew thread would be with no radius.
Has anyone ever seen this before and was it a common practice?? This machine could be about 30 years old.
This evening I am going to check out some ballscrews that a dealer in used machines has on the shelf. Don't know if any can be adapted to fit. If not I will attempt to make a new srew and perhaps new nuts.
Any ideas will be appreciated.

Paul G.

[gvasale]

I don't know if this helps but, there have to be al least 25 ball screw rebuilders. See if you can find a copy of Modern Machine Shop magazine. Usually at leat one or more companies advertise ther. May also be in other publications.

[JCHannum]

You can also buy screw stock and nuts, there was listing in the latest HSM.

Probably easier to buy or have rebuilt. I would think they are hardened, and this adds a degree of difficulty to making your own.

I am not an expert by any means, but all that I have seen have been round in shape, no problem to grind a round nose cutter though.

[Thrud]

Paul
To assist in your cap screw connunderum you might want to consider a set of Bondhaus Ball drivers - you can get them in metric, Inch, Robertson, Torx, L-wrench, T-handle, Folding set, and screwdriver styles. They can keep you from going insane sometimes - worth a look.

Your ball screws sound really, really old. Most of the cheap ones today are rolled, the best are turned and precision ground. Ballscrews today use the radiused groove for higher loads.

www.ahha.com used to sell nice replacement ballscrews for bridgeports for about $600/set.

[Paul Gauthier]

gvasale: When I removed this screw the first time I did check into rebuilding, It would have cost more than a new screw, so I decided not to.

Thrud: I have bondhus ball drivers, never gave them a thought but will give them a try when I replace it.

JC: Great minds must think alike. Your idea is what my friend and I came up with. 1.25" 4 TPI acme threaded rod and matching bronze nut with flange to be machined for proper mounting. Cost so far $109.00. Did I mention they are left handed. No they are not hardened but I opted to purchase the rod instead of making it.

Thanks all for suggestions will keep you abrest of progress.

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Paul G.

[metal mite]

Paul,
Seen those machines at sales and such.
How accurate are they when in good condition?
Got a hydrolic tracer with bout .005 backlash in the x ballscrew.
Some expert told me I could put in oversize balls?
Don't know for sure.
Will be interested in your replys.
mite

[JCHannum]

Most "experts" have big balls.

[Paul Gauthier]

Mital Mite
When in good condition they should have been capable of +- .005 when tracing. My machine has never been capable of such because of the condition of the ball screw being so worn. I have not used the tracer in years, but because it had a tracer it gives me power feeds and rapid traverse in both X and Y.

These optical tracers are only as good as the line it is following. One needs a special pencil or pen that would not leave a fuzzy line. If it did the tracer would see it and the edges of you cut would not be smooth.

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Paul G.

[gvasale]

Paul: good to see that you are managing with what mayy be a very cost effective repair. Thank goodness I haven't that problem. Most things like that are a tough nut to swallow. I wanted a new quadrant gear for my lathe until I was told the price was $500.00. I'm using it as is right now, but I've got more than my arm up my sleeve. Let us know the results of your endeavor. Greg Vasale

[Sprocket]

Check out www.techno-isel.com for ball screw assemblies. Don't know anything about the company, just saw an ad.

[Paul Gauthier]

Greg:
What make and model lathe do you have????

Metal Mite
I your tracer "3-D", had one at my other job (same company), it was the knee that gave the 3rd axis. Does you machine have the large "T-ram" on which one can mount another head and thereby make two parts at one time??? I have the large ram but only one head.

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Paul G.

[metal mite]

Paul,

It's a Cinncinatti Contourmaster
Z axis is on the spindle.
It's about the size of a Bridgeport.
It was made in the late fifties for die work.
The x axis has bout .005 backlash so tracing a hole is only that close.
Real nice making "castings" from solid.
I trace someone's couplers for my trains.
They need a little work with the dramel tool when done.
It works real nice for 2 axis stuff.
Have to make transition points (where x goes plus to minus) at a corner for the best job to avoid a little step.
Can put a pointed stylis in to copy hole locations too.
Adjust your stylis diameter for "tool Comp"
I call it poor mans CNC

Jchannun,

Guess I ain't no expert, only need a thimble to carry mine. Just need a box (to stand on).

Mite

"See the happy moron, he don't give a darn.
Wish I were a moron, gosh I bet I are!"

My late dad used to sing that when someone did something realllllly dumb.

[gvasale]

Paul: Leblond Regal 15x42, built 1951