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Lightweight shaft for air bearing

2004

I am trying to find a shaft suitable for use with a commercial air bearing. The manufacturer supplies solid steel shafting, but this is too heavy for my application - ideally I would like a weight for a 1/2"OD 6" shaft of a few tens of grams. It is required to slide horizontally and rotate over an arc of 90degrees - it does not revolve and is not otherwise stressed.

The manufacturer gives the following specification:

Surface finish: 58-63 Rockwell "C" 10-16 RMS
Shaft size 0.5" +0 -0.0003

Does anybody know if there is a suitable aluminium alloy/titanium/w.h.y available off the shelf, and if not what is the nearest I could get, and how might I finish it to achieve the above specification?

Any comments/ideas very gratefully received.

Bill Hibbert
Hobbyist - London, England

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I would suggest thin walled titanium tubes. They are available from specialist metal suppliers or you may be able to get them from specialist model suppliers. Aluminium is not as light as titanium, nor as strong.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004

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Mark your calendars, everyone, it's a very special and unusual day: Trevor has made a mistake :-)

Magnesium is the metal that is lighter than aluminum. Titanium is nearly twice as heavy as aluminum, although it is indeed very strong.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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Ted, you're right. But pound for pound titanium will be stronger than aluminum.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004

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2004

I have now tracked down a source of 1/2" titanium tubes. These have been measured and are 2 thou over. I have found a precision grinder who *might* be persuaded to grind them (he does not have the necessary grinding stone in stock), but he can only offer +-0.5 thou tolerance over this length (200mm), he says because he "is not temperature controlled".

Thermal coefficient of expansion of titanium is less than steel, so perhaps this does not matter so much, but still seems a fair way out of spec.

Anybody else who might do it? Is it technically feasible?

Thanks,

Bill Hibbert
- London, UK