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The problem with ballscrews on a standard mill

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Posted By: Nick on the Chaski forum
January 2002

What all is involved in a ballscrew conversion for an import mill? I have seen specific kits for Bridgeports, but I have never seen a specific kit for an import knock-off. Is a kit for a bridgeport of similar size (9x42) going to give me enough of a 'parts kit' to get the job done? The mill in question is an Enco 9x42, model 100-1530. I am not converting to CNC or anything like that, just like the idea of "zero" lash if I have to readjust the semi-worn leadscrew anyway.
TIA, Nick



Reply by: Doug C.
January 2002

In Response To: ballscrew conversion (Nick)

Nick,
Not to discourage you from doing this but, using a ball screw on an older manual mill could cause you more grief than any luxury you may gain.
Specifically it has to do with climb cutting. The thrust friction of these screws tends to grab the table and try pulling it out of your hands.
It will happen when you least expect it and possibly more than once.
Operators tend to keep the table locks on snug and this leads to greater wear in the ways. Not to mention if the wear is bad enough already. If it tightens up on each end of the travel so a happy medium during the cut loosens up the table lock then pulls the cutter at .25/tooth rather than .0025/tooth.
Leaves a neat pattern but hell on them cutters even if the part survives.
Mine has them but it is CNC capable also, so technically it needs them for low friction. When I use it in manual mode, I really hesitate to climb cut from experiencing the brown trouser award when it's to late to often for my comfort.
If you have ever used a mill converted to these then you may well know what to expect.
Be it my money on a manual mill, I would invest in a DRO first and replace the old screw later. Ball screws ain't cheaper and inch for inch they could have more error, regardless of zero backlash.
Best of luck in your search.
 
I have an old cinncinatti contourmaster tracer mill.
It has ball screws, as well as handwheels and can be used as a manual mill.
Built in are brakes on the feed screws.
Don't know how they work but with them off you can push the table with your hand.
I can feel it pulling into the cut at times if I forget the brakes on one axis or the other.
I take the brakes off for "rapid moves".
Good thing is only .001 backlash on y and .005 x (some is in the gearing).



[This message has been edited by kap pullen (edited 01-22-2002).]
 
I've changed several sets of leadscrews on off brand machines. In particularly Alliant and Wells, and the machinist love them. Of course, while I have the table off I check the geometry of the underside with parallels and mic. the bearing surfaces and scrape and shape as necessary. But, I've never heard nothing but good responses from the machinist.
 








 
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