# Needle roller bearing tolerances/fit



## picclock (Jul 4, 2012)

This is the first time I've ever contemplated using a drawn cup needle roller bearing and I'm a little unsure of the process and problems/issues. I'm intending to use it in Aluminium and I'm puzzled about the housing tolerances. My intended size is 10mmx14mmx10mm. The table on the right specifies an R6 or R7 tolerance for alloy, which when I looked it up on the net, appeared to be exactly the same as H6 H7. Can anyone tell me the reason for the change of letter (H to R) ? I sort of planned on getting a 14mm H7 reamer and then just pressing them in (although I have no idea of the force needed), possibly with bearing lock or epoxy to retain, depending on insertion force. I intend on using silver steel for the running shaft. 

Any help or advice about these bearings much appreciated.

Best Regards

picclock


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## mzetati (Jul 4, 2012)

The letter offsets the zero line

http://www.tribology-abc.com/calculators/iso_holes.htm
http://www.tribology-abc.com/calculators/iso_shafts.htm

Marcello


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## picclock (Jul 4, 2012)

@ Marcello

Thanks for the links - looks like I might need two reamers (if I can get an R7 one) or I may have to do some accurate boring on the lathe. I looked at quite a few pages but none of them clearly identified the issue as those links did.

Many thanks

picclock


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## Dave G (Jul 4, 2012)

HI Picclock, few things I have learned about neeedle roller bearings over the yrs. The shaft that the rollers run on should be at least RC 56 - 58. Chrome shafts don't last as the chrome will fatique. Full compliment needle rollers work best in high load slow moving applications. Needle rollers with a separator work best at handling rotational speeds. 

The bore that the roller bearing presses into should be round, reamed holes normally aren't round, I would bore then hone to size. The bearing if pressed into a bore that isn't round will take the shape of the unround bore limiting roller contact. Ream a hole some time and then sweep it with a tenth indicator and watch what the indicator says. 

Hardened inner races are offered that fit the needle roller bore from the bearing makers. There is case hardened polished rod available that we called Thompson rod, it is used for linear bearings and can used here also. It must be cut with an abrasive as the case is RC 62. Hope this helps, Dave


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## mcostello (Jul 4, 2012)

Tried Silver Steel once, failed miserably.


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## picclock (Jul 5, 2012)

@mcostelo

Why did it fail - what was the problem? Was the rod hardened ?

Commiserations

Best regards

picclock


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## mcostello (Jul 5, 2012)

Rod was supposed to be marginally hard enough. It was not. Lasted about a month or 2 on a riding mower gearbox.


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## picclock (Jul 6, 2012)

@ mcostelo

Had you hardened the drill rod or was it used as is ?. Unhardened its only around mid 20's rockwell C, but hardened its supposed to be over 60 - which as far as I know - is pretty hard.

If it was hardened and broke it may be that it needed more tempering or material with more give. It might be worth trying to case harden mild steel with Kasenit or a similar hardening material, assuming that the core would be tough enough for your application.

As I'm planning to fit the roller bearing in Aluminium and the recommended press fit tolerance is R7 ~ -0.5 thou, I'm thinking of making the hole about 2-3 thou smaller then heating the Aluminium part to say 150C and shrink fitting the bearing. As its operating temperature will never exceed 35-40C. This seems like a better way to ensure a good fit. The surrounding metal is only 3mm thick and will stretch to accommodate the bearing as it cools. Seems like a plan at the moment, will post pictures if it succeeds.

One of the things I have to sort out is a way of tempering the silver steel after hardening it. Domestic ovens don't seem to get hot enough, which is a pity, so I think I will have to bite the bullet and brew something up. I suppose what I really need are 36 hour days .. . :

Best Regards

picclock


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## mcostello (Jul 6, 2012)

Used as it arrived. Was told by another machinist it would work, but did not.


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## rkepler (Jul 6, 2012)

picclock  said:
			
		

> As I'm planning to fit the roller bearing in Aluminium and the recommended press fit tolerance is R7 ~ -0.5 thou, I'm thinking of making the hole about 2-3 thou smaller then heating the Aluminium part to say 150C and shrink fitting the bearing. As its operating temperature will never exceed 35-40C. This seems like a better way to ensure a good fit. The surrounding metal is only 3mm thick and will stretch to accommodate the bearing as it cools. Seems like a plan at the moment, will post pictures if it succeeds.



I would double check the amount of shrink - if the press fit is .0005 that's what you should use whether you shrink or press the cup in. More shrink would reduce the cup and remove any chance of the shaft getting into the needle bearings.



> One of the things I have to sort out is a way of tempering the silver steel after hardening it. Domestic ovens don't seem to get hot enough, which is a pity, so I think I will have to bite the bullet and brew something up. I suppose what I really need are 36 hour days .. . :



If you're trying to get drill rod up to RC58 you really need some skill or proper HT equipment, you're quite close to the top hardness in oil hardening drill rod and it will likely not need tempering. Also, drill rod can come out of the centerless grinding process with a non-cylindrical shape, I have some 1.375" O1 that has a .0015" tri-lobe. If the bearing is small enough you might use a hardened dowel pin as a shaft, they're quite round and on size. Another possibility is to buy a liner with the OD needed for the needle bearing ID, the liner will have the right hardness and the shaft may be simply loctited into place (with appropriate care not to lock the bearing). Don't be tempted to use anything chromed and ground to size - if it's spun the bearing needles will work the chrome off in a short while no matter how good the plating.


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