Turning a ballscrew

I have not turned the ends of ball screws. I have turned some "odd-leg" shapes in a four-jaw chuck.

One way to handle the situation is to cast a collar of fixturing metal around the chuckable area, then - warts and all - chuck it up and indicate the work end to true.

Some of the Bismuth fixturing metals have positive, zero, or slightly negative coefficients of expansion upon cooling. The correct one will grip the metal tightly without distortion. The stuff melts at about 250F, so it's no big deal to get it back off after you're done.

I imagine commercial "turners of ball screws" have a mating chucking collet that has inner contours which fill the profile of the screw.

LLoyd

Ball screws are hardened and its unlikely that any gripping force from the chuck could damage the surface, just chuck it up and go- take light cuts until you have broken through the surface hardening. Depending on the length and diameter, you may want to make a bushing for the end that projects from your spindle to prevent whipping and warping.

Jim,

Thanks for the advice. I did think about that, but was not sure that it would not be damaged... Thanks!

The ball screw is 16mm in diameter and the stock is ~1m long, but the finished length will be about 300mm (I'll be making 3 screws). I am thinking of cutting the screw into 300mm lengths before machining. Will I still need to support the long end of it?

Sandi

Jim> Ball screws are hardened and its unlikely that any gripping force from the

You can get aluminum or soft steel jaws for many lathe chucks. Otherwise, the jaw of the chuck is probably harder than the screw and will damage it if you chuck down hard. If you chuck down loose and the piece slips in the chuck, the damage will be even worse than had you held it firmly to begin with.

I would chuck down on an area you're planning to remove and see if the part is damaged. If it is, use a collet to hold the part or soft jaws.

Paper or tape around the part seldom works well.

Fixturing alloy or a soft metal fixture clamp (brass or aluminum) would be a good bet.

I wrap delicate parts in brass shim stock.

Generally a collet is the best (and only good way) to do this. But most ballscrews are harder than a w***es heart on the outside, so dinging one is a bit hard. They are both heat treated and surface hardened (least the good ones) in the screw area, so if you are going into the screw area..grinding may be your best option

Gunner

"Liberalism is a philosophy of consolation for Western civilization as it commits suicide"

- James Burnham

Just passing along what I thought was a clever tip from another forum: If screw thread marring should prove to be a problem, first clean the threads then spiral wrap wire in the threads where the chuck/collet jaws make contact. The wire diameter must be smaller than the screw thread pitch spacing but large enough to protrude above the thread crests. If using 5C collets, I presume it essential to prevent collet damage that the diameter over the wire wrap be within a few 1000ths of the collet ID, preferably a bit over, allowing for some radial compression. The wedging action of the wire is apparently effective in resisting slippage of the threaded part in the chuck/collet.

David Merrill

I thought the ball screws I have here use a grooved, ground and polished helical race. Gripping to major diameter should have nothing to do with the ball grooves....?

I tend to agree. Also, we keep copper shim stock around, which helps to protect more delicate items when gripping in lathe chuck jaws, or whathaveyou.

True, the nut never touches the screw. Only the balls touch where they contact in the grooves.

Still, try not to make any major marks on the OD of the screw.

Thank You, Randy

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We use Al. soda cans and anealed Al. flashing at school to prevent marring things in the chuck. ...lew...

Use properly prepared soft jaws for the project, gripping the cut-to-length pieces of screw and you won't have any problems.

Harold