Recirculating balls OK on hardchromed shafts?

[stumax]

Hi guys, just found this forum - great! I've been working on my own design mill for a while now. It will have a travel of 1500mmx1000mmx500mm. Due to the high cost of hardened/ground steel shafts down here I've used hydraulic cylinder rod, which is 4140steel hardchromed and centreless ground. It has a great surface finish (as good as "real" linear shafts) and the steel is hard-ish but soft enough for me to cut with a hacksaw and drill & tap zillions of holes in it to fix it to the alum rails. I was originally intending to use Permaglide bushes in home made housings, and I made up a set however the friction is very high. One of the linear bearing suppliers payed a visit to my work a while back and showed me some fairly inexpensive open type recirculating ball linear bearings which would be cheap enough for me to fit to all axes. He said that the hard chromed shafts would be OK with recirc. balls running on them, but a few machine designers at work say the balls will chew up the rails in no time. It's not a super heavy machine, but it is constructed from 2" sq x1/8" wall steel tube, so it's quite a bit heavier than the alum framed ones I've seen here. Does anyone have any experiences with recirc. balls on chromed shafts they can share with me? BTW, the machine's kinda covered with RC plane stuff at the moment but as soon as I can see it again I'll snap some pics to share.

Thanks in advance

Stu

[HuFlungDung]

Hi Stu,

Maybe you just need to "prime" those permaglide bushings to free them up? If you want to run them dry, try working some dry graphite powder into them. This stuff you can find at hobby stores. I think Model railroaders like to use it.

I would suspect that the recirculating balls might indeed loosen the chrome plating. Hardened shafting would be the best choice.

[xairflyer]

Have you looked at Simplicity bearings from Pacific Bearing

http://www.pacific-bearing.com/produ...oduct.cfm?ID=1

[stumax]

Thanks guys. I have tried all types of lube on the rails but the stiction is still quite high, which I suspect will create problems when doing point-to-point motion. I think the problem is because Permaglide bushes are closed section and I epoxied them into a home made housing then milled a slot in them to allow for the rail. They're de-burred but I suspect they not too round anymore.

I saw the Simplicity bearings from another post, they look interesting, I've seen a similar product locally, but they were a bit more expensive than cheap recirc. ball linear bearings. Does anyone have experience with them?

thanks!

[Pelle76]

Originally posted by xairflyer Have you looked at Simplicity bearings from Pacific Bearing http://www.pacific-bearing.com/produ...oduct.cfm?ID=1

Xairflyer!
Those linear bearings look real good. Do you know in what price range they are? Are they affordable enough to be put on a MDF-router?

[mikeschn]

The stick-slip action is something I hadn't thought about. Mine is stick-slipping a little bit already. Does anyone recall their gantry having a stick-slip problem while assembling, but not having a problem while actually running the machine???

Mike...

Originally posted by stumax Thanks guys. I have tried all types of lube on the rails but the stiction is still quite high, which I suspect will create problems when doing point-to-point motion. thanks!

[xairflyer]

Re Simplicity bearings

The cost is excellent, much cheaper than ball bearings (I worked out on average about 3 times cheaper), contact pacific and they will send you a sample, I am in Eire so prices will be different, a 3/4" size is about €20

[ballendo]

Hello,

I just answered this question in another thread. Unfortunately I'm new here and don't know how to find what I've already written to guide you to it...

The short answer is that the engineers at work are right...

You CAN get hydraulic shafting with a case hardened surface under the chrome. If you have that type, you're good to go.
If not; better look at the plane bearings being mentioned...

Hope this helps,

Ballendo