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Old 03-25-2014, 10:33 AM
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mikeconcannon mikeconcannon is offline
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Default Rotorhead Bearing, advice sought

Hello, I believe that this is about the best that can be got, for use in a Bensen style rotorhead on my Campbell Cricket. Do I have that right??
Also does it have to be mounted writing up or down, or does it not matter on this kind of bearing.
Thanks in advance, mike
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Old 03-25-2014, 02:42 PM
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Mike
3206 = 30mm bore, 62mm OD
A = "A" design meaning no filling slots
2-RS1 = Rubbing seal of synthetic rubber with sheet steel reinforcement at both side of bearing
TN 9= Moulded cage of glass fibre reinforced polyamide 6.6)
MT = Grease for medium temperatures (-30C to + 110C)
33 = the identification of the actual grease applied to your bearing. The SKF book says that the MT suffix is only used if the grease is not the standard for the particular bearing. This seems to imply that the grease in your bearing isn't the standard, although the SKF website says :
" Bearings in the 32 A and 33 A series are filled with a high-quality NLGI class 3 grease with a lithium thickener and are marked with the designation suffix MT33. This grease has good corrosion inhibiting properties and can be used at temperatures between 30 and +120 C. The base oil viscosity is 98 mm2/s at 40 C and 9,4 mm2/s at 100 C."
So you're looking good and no it doesn't matter which way up you install the bearing because you haven't got any" filling slots".
Mike G
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Old 03-25-2014, 02:59 PM
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thanks mike, i should have just phoned you! So you think l won't go to far wrong with this bearing then?
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Old 03-25-2014, 03:43 PM
Alan_Cheatham Alan_Cheatham is offline
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Here is an issue of concern and others more knowable should chime in.

There are several cage materials that these bearings can come with, I believe the older bearings that were used in rotorheads used steel cages.

Are non-steel cages, especially brass and high tech plastic, appropriate in life-critical rotor bearings?


TN 9= Moulded cage of glass fibre reinforced polyamide 6.6


http://www.skf.com/us/products/beari...ges/index.html


http://www.skf.com/us/products/beari...als/index.html


.

Last edited by Alan_Cheatham; 03-25-2014 at 03:48 PM.
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Old 03-25-2014, 04:35 PM
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A point worth addressing.....
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Old 03-25-2014, 04:44 PM
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Default if my memory

If my memory serves me correctly I thought these bearings should be in teh 5206 family? Is there a difference between the 32xx and 52xx?
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Old 03-25-2014, 05:18 PM
Alan_Cheatham Alan_Cheatham is offline
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This is from the SKF site:

http://www.skf.com/us/products/beari...ngs/index.html


"Bearings in the 52 and 53 series, in accordance with ABMA standards, are no longer available from SKF and have been replaced with 32 and 33 series bearings in accordance with ISO. With the exception of size 3200, 32 and 33 series bearings are dimensionally interchangeable with bearings in the 52 and 53 series. Size 3200 has a width of 14 mm instead of 14,3 mm."


SKF owns MRC I believe. MRC bearing info is on SKF's site here:

http://www.skf.com/us/products/mrc/index.html

http://www.skf.com/us/products/mrc/d...ies/index.html

According to this document the 5000 series of which the 5206 is a member used:

"Ball Cages and Types
The cage supplied with C-type and M-type bearings is
a one-piece crown-type of heat-treated pressed steel. It
is snapped into place after the full quota of balls has
been introduced between the inner and outer ring."

http://www.skf.com/binary/30-97834/519959-.pdf


.
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Old 03-25-2014, 11:52 PM
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Mike
I was tempted to recommend solid brass cages but didn't because I didn't feel they were really necessary for this application. They would be nice but IMHO not necessary.
I spent the last 10 years of my career sitting on the American Petroleum Institute (API) task force writing, among other standards, API 610, the world-wide Oil and Gas Industry standard for pumps in hazardous service. One of the major discussions was about rolling element bearings and API 610 always required solid brass cages.

I was also responsible for writing my company (the 5th largest oil non-state oil company in the world) standards for rotating machinery and wrote pressed steel cages out of our specification because of the cage failure mode which put lots of fragments into the bearing whereas solid brass cages didn't tend to break up into small pieces and were far superior. I also wrote out the 6.6 polyamide cages but that was more a temperature concern. Don't forget I was writing specifications for machines that were expected to run for 3 or more years non-stop and the bearings were often loaded to as near maximum load and temperature as possible so we're not talking about the same sort of service.

Gyro rotor bearings are not very highly loaded and do not run at high temperatures or speeds or for long periods but if you want a Rolls Royce bearing then go for a solid brass cage so it would be 3206 A 2-RS1M MT33.

If I had a concern about this bearing application it would be that there isn't very much side (or radial) load, most of the load is axial. These bearings do have a minimum radial load requirement,
http://www.skf.com/us/products/beari...oad/index.html
this side load is needed to reduce the risk of the balls skidding but again this is more a high speed problem that shouldnt be of concern to us.

At the end of the day this is all pretty hypothetical because Bensen gyros have been operating for years now with these bearing and probably steel cages and any bearing failures that have occurred are most likely due to maintenance failures than bearing being badly selected.
Mike G
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Old 03-26-2014, 02:47 AM
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Thanks again Mike. Its good to have the definative, qualified answer to the question of, what is the ultimate rotorhead bearing?
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Old 03-26-2014, 07:38 PM
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Very well said Mike G. I learned.
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Old 03-27-2014, 05:35 PM
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Mike I wouldn't call the 3206 the ultimate bearing for a rotorhead application. In fact IMHO it's a pretty poor choice.
I would have preferred a matched pair of 40 angular contact ball bearings mounted in a back to back (called "O") arrangement with brass races and a built in pre load. That would be something like 2 off 7206BEGB 2-RS1M MT33. This arrangement would 8.6 mm longer and 4 ounces heavier but could absorb much higher axial loads and would be stiffer in the rocking mode. The pre load would also prevent/reduce brinelling during transport and taxying.

However Bensen's choice was a reasonable, pragmatic, low cost, easy to purchase solution that has done the job for years so I can't really criticize it.

Mike G
PS You can't put pre load on a 3206 bearing but you could go for a reduced clearance (C2) to help combat Brinelling so my Rolls Royce 3206 would be 3206 AC2 2-RS1M MT33.
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Old 04-28-2014, 04:29 PM
Flyonnawall Flyonnawall is offline
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Default Bearing the Frustration!

Quote:
Originally Posted by mikeconcannon View Post
Hello, I believe that this is about the best that can be got, for use in a Bensen style rotorhead on my Campbell Cricket. Do I have that right??
Also does it have to be mounted writing up or down, or does it not matter on this kind of bearing.
Thanks in advance, mike
Hello! Noobie here :

I need to find a place to purchase the : 3206 AC2 2-RS1M MT33 bearing.
In Vicinity of S.E..Texas......Or else online.

Since I fear the material quality of foreign purchase points, West of the Pacific......

I went to the SKF website and filled out the form for finding a distributor,

And those undecipherable "Captcha" codes that even someone with 20/20 vision needs an interpreter to figure out!!!
and got nowhere!!

I Filled out form to have them email me... The info
And again with the frakin "Captcha".

Still zilch!

What a runaround for a single purchase!


Thanks!
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Old 04-28-2014, 04:51 PM
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Hello Charles (Flyonnawall). Welcome to the forum, it may be a good idea to go to the Welcome Mat forum and introduce yourself. We have a very active chapter in Anahuac, it would do you a lot of good to come and visit us. Take a look around on our website at gyrosaway.com for more information. Download and read some of our newsletters at http://www.gyrosaway.com/newsletters.php. We have 18 gyros in our three hangars, two more are in another hangar at the same airport. You can probably catch a ride with someone and get a lot of information about gyros. Who knows, we may even have the bearing your looking for. We are usually there every Saturday.
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Old 04-28-2014, 10:45 PM
Flyonnawall Flyonnawall is offline
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Quote:
Originally Posted by Mike484 View Post
Hello Charles (Flyonnawall). Welcome to the forum, it may be a good idea to go to the Welcome Mat forum and introduce yourself. We have a very active chapter in Anahuac, it would do you a lot of good to come and visit us. Take a look around on our website at gyrosaway.com for more information. Download and read some of our newsletters at http://www.gyrosaway.com/newsletters.php. We have 18 gyros in our three hangars, two more are in another hangar at the same airport. You can probably catch a ride with someone and get a lot of information about gyros. Who knows, we may even have the bearing your looking for. We are usually there every Saturday.
Thanks Mike,
I am aware of Anahuac, that's PRA 62 no?? I have had an email with Mark S.
who also invited me.
Saturdays are a slight problem for me to travel. Most of my customers are only available weekends.... And being retired.... Or trying to be, gets tricky.
I have already trip planned the route in my GPS...and it is a two hour trip for me. That's one way. Not a big deal for a Texan.... But I have relocated from a much smaller state where in two hours you could travel the entire length, and breadth of the state... well..... Almost!

But I would certainly love to catch a ride...
Will certainly go feet dry, at the Welcome mat, and introduce self.

Charlie (flyonnawall)
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  #15  
Old 04-29-2014, 04:20 PM
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Charles (Flyonnawall)
My selection of a 3206 AC2 2-RS1M MT33 bearing was really an academic exercise to try to help members understand a little more about bearing selections. As I wrote earlier the original Bensen choice was not the best but was perfectly adequate for the job and easy to find, the ultimate bearing I specified may be very difficult to find and hence expensive.
Don't forget most bearing failures are due to poor lubrication, corrosion or poor installation not poor selection of the bearing for the service.
Mike G
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