ball screws warped!

[mre1000]

I bought from mcmaster.com three 1” ¼ pitch ball screws in December. The sizes where 24”, 48” 60”. I just machined the ends of the 24” with not problems, but when I went to machine the 48”, I noticed that the screw was warped!!! So I then put the 60” in the lathe and it also has the same problem. Just to make sure I took them both and rolled them on a flat surface to confirmed the problem. I am going to call them to exchange do an exchange, but I am nervous it’s going to happen again.

Has anyone else have the same problem?

[sendkeys]

how much warp? nook screws run around .010 inch/foot max. they say no more then .03 over 6 foot. but nooks screws are very nice. Not sure who makes the mcmasters screws.
(edit)this if for rolled screws, if they are ground, you should yell until you get some new ones (edit)

Also i have seen this a couple of times, you can also warp them yourself to if you dont support them when they are on the lathe.

If they dont exchange you can always straighten them.

goodluck

[NC Cams]

Residual stress in parts can cause them to warp even while sitting. Rolled screws would surely have residual stress potential.

We ground some special welded billet cams. Straight as an arrow when we shipped them - warped nearly 0.012" TIR while shipping. The grinding reduced residual stress generated while welding and, whah-lah, pretzels.

From my experiences of late, this would not be surprising in a rolled thread part that wasn't properly stress relieved after processing.

A person adept at shaft straightening could either cold or hot straighten them. Better yet, take them back and let someone else deal with it.

A press can straighten them with care. You could even load down the ends and pry up in the middle with a 2x4 and straighten them adequately for use - again with care.

[mre1000]

They both deflect about .150. I called mcmaster, they were very nice and said just send them back and they will send new ones. I think I am going to drive there though, I live in Des Moines, IA so it’s about 6 hours from me. I think the shipping cost would be about the same as my gas. They have plenty in stock, so I can make sure that I get un-warped ones, at least I hope to.

Here’s another question, if my screw have any deflection in them, let’s say .01 won’t that make my table have a deflection of .01 every rotation of the screw, or will the rigidness of my linear glides stop it.

[buscht]

mre1000, Make sure you get the name of the person who said to send them back and a proper return authorization number. I went through a similar issue, (wrong length) mailed them back and got new ones. I was charged for the new ones but never got credited for the old ones.

Because I didn't have any numbers or names, I had no proof of the problem.

[sendkeys]

good thinking buscht

[NC Cams]

Re; table deflection induced by screw warpage.

It all depends on how rigid your table is and how rigid the linear guides are that support same.

If the screw is stronger than the ancillary hardware, the hardware will move. iF the hardare is stiffer than the screw, screw will conform. A simple variation of the weekest link axiom.

Edit: the deflection is a function of CLEARANCE combined with any deflection potential due to the deflection from the screw overcoming the rigidity of the linear guides as it may be able to do.....

[motomitch1]

Originally Posted by mre1000 Here’s another question, if my screw have any deflection in them, let’s say .01 won’t that make my table have a deflection of .01 every rotation of the screw, or will the rigidness of my linear glides stop it.

Yes just a little bit it wont be .010 it will be the amount of clearins you have in you linear glides or gibbs.