very low torque bearing assembly 2

[1MadMax]

I am tasked with resolving a bearing requirement in a low torque assembly, bearing size is 1634 (1" o.d.x .75 bore dia.). It is a thin section ball bearing .156" (4mm) thick. There is very little loading on the bearing. The assembly osilates rapidly around 7-8 Hz however preliminary assessment (pre-build) of the bearing is done by spinning the bearing and by "feel". We have tried cleaning techniques and run-in procedures to brunish any incidental retainer contact with some limited success. The best we've been able to find to date is to purchase ABEC7, P25 bearings supplied dry and sorting the shipment for "good ones" (yield fluxuates from 80% to 0%), then try to assemble these into full-up assemblies without contaminating them in process. Does anyone have knowledge of a cleaning or other process which provides ultra free running results for contaminated bearings and supplied bearings that are inadequate? Keeping in mind optics are involved so out-gassing must be avoided. I realize this is a very unique application and any help/insight would by appreciated.

 

[rb1957]

how about magical (sorry, magnetic) bearings ?

 

[1MadMax]

Hey Magical would be good but likely equally difficult to source!
I'm not sure that magnetic bearings will work. In short the bearing goes in a sub-assembly that is essentially a mini magnetic motor. The design and assembled unit are in production and have been previously optimized to the limits of the building specification from the customer. Wouldn't the magnets potentially interfere, also this a small, low voltage assembly about 1.8 volts max to function at 7-8 Hz.
Is it still sound feasible?
thanks

 

[israelkk]

In addition to the ABEC accuracy number of the bearing it is customary in some cases similar to yours to ask the bearing supplier/manufacturer for a specific guarantied "starting torque" and "running torque" of the bearing. You should consult the bearing manufacturer for the specifics of your design.

 

[1MadMax]

You are correct and I have been working with 2 bearing suppliers/manufacturers to see if they can benchmark the torque requirement I need ... so far no go. Its difficult to image how sensitive the application truly is, my initial response when I first became involve was "You're joking ... right?" I have tried bearings with Teflon slug retainers which are supposed to be ultra low torque, they didn't come close. I wanted to try using only 1/2 the balls in the retainer to reduce drag but they long lead, special order.
thanks

 

[unclesyd]

Could you possibly use a C-Flex Bearing for your application. We use a lot of these for similar service.

http://www.c-flex.com/home.html

 

[Timelord]

1MadMax,

I have had some experience with your bearing selection problem. While I was with Goodrich Aerospace I designed the little gimbal that replaced the periscope between the pilots legs in the U2.
I have had the best luck with hybrid bearings i.e. stainless races, ceramic balls, a solid lubricant plated to the races and a moly loaded plastic retainer. Size the bearing bore to so the press fit reduces but does not eliminate the minute radial clearance in the bearing. Run them dry or lube with a single drop of vacuum pump oil. This combination give the lowest running friction possible short of using a gas or magnetic bearing which have their own set of problems, of which size is only one.
Check out Champion Bearing:

http://championballbearings.com/

They specialize in this type of bearing and they can deliver quickly.

Timelord

 

[1MadMax]

Unclesyd and Timelord,
Thanks for the great tips, I'll follow these up this morning.
Timelord you are absolutely on the money with your gimble project, it directly compares with this application. I considered and investigated hybrid bearings just as you've described but found both suppliers wanted in excess of 6-8 months lead for delivery and large minimum quantities. Did you also find this? What about cost? Were you ever required to clean and re-oil these bearings, if yes could you share that experience? The outer race is not pressed in but rather bonded with the inner osilating.
thanks again!

 

[GBor]

1MadMax,

How about giving Unclesyd and Timelord a "star", which is a vote for "TipMaster of the Week". Simply click on the "Thank ____________ for this valuable post!" and confirm. It helps people identify helpful threads in the thread list and helpful posts within the thread.

Thanks,
GBor

 

[1MadMax]

GBor - Got ya ... both done, thanks

Unclesyd - I checked out the C-Flex bearings, I'd never heard/used them before. They look interesting and I'll keep them in mind for other applications, however the bore diameter on this project has a small assembly mounted inside it. I should say now that there is no press fir on the bore dia. either, thus no radial loading on the bearing to effect performance.

 

[Timelord]

1MadMax,

Check out the link in my first post. I have purchased hybrid bearings with custom seals from them with less than 4 weeks delivery in quantities of less than 10. They do not manufacture the bearing parts, but modify and reassemble, so if you stay with a size that is readily available as a standard bearing they can react relatively fast. It took me years before I discovered them and previous to that I also was frustrated by long deliveries and large minimums, which can kill a project when individual bearings can cost upwards of several thousand dollars (I've worked on gimbals with large holes thru the axes).
As far as cleaning goes, we used an ultrasound cleaner with various solvents or soap and water. Gently blow dry with canned or filtered air and wrap in lint free paper. We assembled the gimbals in a cleanroom.

Timelord

 

[unclesyd]

Appreciate the recognition for the C-Flex link. It's been awhile since I've had contact with them but they have capabilities beyond what is in their brochure.

You might want to checkout the folks at Dynaroll. Aside from bearings they can give you a bearing's mechanical parameters, which might save you time and effort of testing in a prototype.

http://www.dynaroll.com/testing.htm

If you ever need a few precision miniature bearings for prototyping and testing here is a very good source of one to many. I'm running one of their bearings @ 300,000 rpm and it's doing fine.

http://www.bocabearings.com/

 

[1MadMax]

Timelord - Yes I checked out the link and fortunately they open at 6am so I was able to phone them this morning! They sound good, I wasn't aware of the fact that they don't manufacture their own bearing.
I am stuck with the bearing size ... no options there. They said it was not a real popular size but still gave me a 2weeks delivery and a verbal quote during the call, which impressed me.

Unclesyd - Thanks for the additional resources.

 

[Clyde38]

Seems like you have been given some pretty good answers already, but you might just want to run this by the Bearing design, manufacture and maintenance Forum.
forum821

 

[1MadMax]

Clyde38 - I'm newly subscribed and completely ignorant to the format and resources available here.
thank you Max

 

[1MadMax]

Clyde38 - What is best to do ? Start a thread in the suggested forum or is there a way to link the existing thread directly? please advise

 

[Clyde38]

Good question. I believe that double posting is frowned on. Perhaps one of the more seasoned members can help. You could click on the

http://www.eng-tips.com/market.cfm

link and scroll down to the e-mail Management link and ask.

 

[IRstuff]

You can try clicking the Inappropriate post link and ask that the entire thread be moved to the appropriate forum.

TTFN

FAQ731-376

 

[unclesyd]

Here is something you might be interested in for your cleaning and lubrication. The first is the Micro Care site that has products based on DuPont's Vertrel line of solvents. They have the capability of no residue cleaning of a bearing and then as a carrier for a dry film lubricant.
Vertrel has a myriad of uses above and beyond the above.

Next is The Bromothane line of cleaning solvents again form Micro Care. This is a very good cleaner for precision parts, both hot and cold.

http://www.vertrelsolvents.com/product/Default.htm

http://www.bromothane.com/FAQs/FAQ.Q20_Applications.html

 

[1MadMax]

Thanks Unclesyd, I'll have a look at the sites posted.

Clyde and IRstuff - I'll see about moving the thread.