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Instrument bearing static friction?

I'm an electronics guy playing around with an instrument design that uses light weight 1mm diameter s/steel cable to rotate a sensor shaft mounted in two small bearings.

The sensor shaft starting torque needs to be as low as possible - less than

0.08 inch-ounce

I'm looking at using a couple of R4ZZ bearings - 1/4 (6.35m) ID x 5/8" (15.875mm) OD x 5mm wide.

I've looked at several data sheets for these bearings but have not found a static / startig torque value. Is this something that is generally stated for bearings?

I will also need to test the starting torque of the shaft assembly. With such a low starting torque value the only way I can think of doing this is to fit a blanced disk to the shaft and place increasing sized little balls of poster putty / blu-tac on until rotation occurs, then weigh the putty applied etc. It seems a little unwieldy and probably not too accurate. Is there a better way?

regards rob

Reply to
Rob
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How about you glue a cotton thread on that disk's periphery at 3 oclock, and place an aluminum foil tray on the end of the cotton. Then you can use regular analytical balance weights, which start at 10 mg or so - they cost about $15 for a student set.

Bearing's friction is controlled by the grease fill they may have. For some critical apps, people wash out the grease altogether....

Brian Whatcott Altus OK

Reply to
Brian Whatcott

How about a torque watch gage?

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that on the end of your assembly and it will give you a very exact reading.

As for grease...it is *not* the grease that effects start up torque as much as you might think. Ball size, ball weight, cage design and type, contact between balls and raceways, race curvature, seal drag (if the bearing has seals, the clearance in the bearings, the load the bearings is carrying and numerous other considerations all contribute to starting torque in a ball bearing.

You'd be better off considering an ISO series bearing (600 series) rather than an R series bearing.

Reply to
kacannon

snipped-for-privacy@mindspam.com wrote in news:doilpq$nf1$ snipped-for-privacy@blackhelicopter.databasix.com:

We used to use self aligning bearings, and rip the seals out, and flush the grease out and use WD40 instead (although I think a light oil might be a better bet). Always use the smallest OD bearing you can find, if low torque is your highest priority. Self aligning bearings tend to have lower friction than deep groove bearings.

Cheers

Greg Locock

Reply to
Greg Locock

Thanks for the advice guys. I'll probably give Brians cotton / weight idea a try. The Watch gauges look great but are a likely to be too costly at this stage.

I had a look at 600 series bearings, they didn't appear to go as large as

1/4" ID - at least not on the sites I found.

With the current R4ZZ bearing in a brass housing am I likely to have any major corrosion or other issues (over say 5 years+)?

The units are located in the field bush / desert / forrest / riverside / seaside / pier etc) and are mounted inside an encosure to protect against the weather. The outer side of one bearing is exposed to the water surface via an air column anything from 4' to 20' long. Direct wetting is not expected. The same bearings in a pvc housing last >10 yrs. Shielded rather than sealed bearings are used to minimise the friction / torque.

regards rob

Reply to
Rob

I beg your pardon?

Brian Whatcott Altus OK

Reply to
Brian Whatcott

I modified my intro...in a funny way and if I unintentionally offended I apologize...I should change that for the serious groups I read.

Reply to
kacannon

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