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Roller Bearing Fit

lr172

Plastic
Joined
Dec 10, 2017
I have a question about bearing fit up. I am building something that has a driven shaft with two bearings. I made the bearings to be a press fit on the shaft and left a .001" slip fit on the outer clearance, as I that was the recommendation by the bearing companies. My question is on retaining these bearings. The shaft will be driven by a gear system with a decent amount of backlash, so I am not sure if I will get any axial load. As I spin the shaft by hand, the bearings spin in housing and if I apply some axial load while spinning, the bearings with spin properly.

I set up the bearing retainer to have .001" clearance as well, but now wondering if I should tighten this up to hold the bearing's outer race captive. The housing is aluminum, so I am afraid of the bearing spinning in the housing and fretting/wearing.

I suppose the fulcrum of gear teeth will apply some axial force and this may be enough. Also, the bearing is brand new and therefore a bit tight.

This is my first work with bearings and would appreciate some guidance.

Thanks for your assistance.

Larry
 
Clarifying what specific bearings you're using would help. You are correct that you don't want any rotation of the outer race and housing, you can clean the surfaces and use a low strength Loctite sleeve retention product to prevent this.
 
I have a question about bearing fit up. I am building something that has a driven shaft with two bearings. I made the bearings to be a press fit on the shaft and left a .001" slip fit on the outer clearance, as I that was the recommendation by the bearing companies. My question is on retaining these bearings. The shaft will be driven by a gear system with a decent amount of backlash, so I am not sure if I will get any axial load. As I spin the shaft by hand, the bearings spin in housing and if I apply some axial load while spinning, the bearings with spin properly.

I set up the bearing retainer to have .001" clearance as well, but now wondering if I should tighten this up to hold the bearing's outer race captive. The housing is aluminum, so I am afraid of the bearing spinning in the housing and fretting/wearing.

I suppose the fulcrum of gear teeth will apply some axial force and this may be enough. Also, the bearing is brand new and therefore a bit tight.

This is my first work with bearings and would appreciate some guidance.

Thanks for your assistance.

Larry

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normally one bearing is held for axial movement prevention and the other bearing has float ability for thermal expansion as if floater held and it binds that can cause problems even shafts bending.
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od of bearing normally has .0005 to .0010" clearance as oil/grease will fill this gap and offer slight resistance but not too much. its true if load on shaft is balanced and bearing is floating in housing it can spin in housing and cause problems. normally some shaft pressure on bearing stops this
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dampening grease is a type of grease that comes in different thicknesses. its used in camera lenses to give smooth motion rather that feel rattling from clearances. when pointing lens down it holds lens from sliding from gravity. i have seen too thick a dampening grease applied and it was too hard to move adjust a optical instrument. basically when applied on bearing od it will resists bearing spinning, if too thick it can actually hold too good almost like sticky glue. sort of like grease applied to screw head to help it stick to allen wrench when reaching far into machine. the screw screwed in and allen wrench will come off screw. its sticky but not like glue
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tolerance ring is used on washing machines where load is lighter and vibration causing bearing spinning in housing so its help with a constant spring pressure
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tolerance ring - Google Search
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vibra tite is a type of rubber paint used on screws. not quit loctite. it holds screw from rattling (moving cause of vibration) but you can still turn screw. it just fills clearances
 
Clarifying what specific bearings you're using would help. You are correct that you don't want any rotation of the outer race and housing, you can clean the surfaces and use a low strength Loctite sleeve retention product to prevent this.

Disagree with this, you will get a lot lot more life out of the bearing if its stationary race can slowly rotate to distribute uneven wear, its where that slight magical clearance comes in.The outer race is then free to act like a harmonic drive reduction so turns only a few revloutions a week if that. Its very very comon on electric motors to do this, other wise things like belt drives would kill bearings off pretty fast.
 
.001" clearance is loose feeling. If the shaft is low speed so that bearing heating is minimal, you could Loctite both bearings in. This may create problems on disassembly, akin to having press fits everywhere.

Ideal clearance is .0003". I use this spec all the time for bearings in electric motor endbells: you can still tap it together with a soft hammer and once lined up, it will slide. The tendency to spin in the housing is pretty low at this clearance. That would be why I virtually never have a comeback. Most commercial motor bearing fits are looser than mine, and they help keep me in business :)
 
Thanks for all of the input here. Too bad I didn't post earlier, as the clearances were a bit tight and I sanded them down :-( I am thinking that I can put about - .0005" to -.001" on the retainer to create a light axial load and keep the bearings from spinning. Is this more problematic than loctite to retain them? The grease idea is interesting and will see if I can find some thick grease.

The bearings are 6202-2RS ball bearings. The spinning assembly is pretty well balanced and there is no load other than the bearings themselves and an oil seal. I probably wouldn't be as worried if there was a belt drive or something creating a side load, but it is gear driven.
 
The spinning assembly is pretty well balanced and there is no load other than the bearings themselves and an oil seal. I probably wouldn't be as worried if there was a belt drive or something creating a side load, but it is gear driven.



What's the pressure angle of your gearset ?
 
Thanks for all of the input here. Too bad I didn't post earlier, as the clearances were a bit tight and I sanded them down :-( I am thinking that I can put about - .0005" to -.001" on the retainer to create a light axial load and keep the bearings from spinning. Is this more problematic than loctite to retain them? The grease idea is interesting and will see if I can find some thick grease.

The bearings are 6202-2RS ball bearings. The spinning assembly is pretty well balanced and there is no load other than the bearings themselves and an oil seal. I probably wouldn't be as worried if there was a belt drive or something creating a side load, but it is gear driven.

Make a couple of "rasp teeth" inside the housing. There used to exists a special knurling tool for a similar purpose. You do not want the bearing lose in the housing.
 
SKF, Timken, and other reputable bearing manufacturers have engineering data available online. That would be my starting point for bearing fitting recommendations. They also have field engineers available to assist you.
 
A lot of bearings are set up as you did it, rotating member (shaft) solid fit and stationary mount can float. I've seen this set up many times in machinery design, automotive timken wheel bearings were always that way and many out lasted the car. Harley transmission main shaft support bearing slides into the chain case housing and is installed with loctite on the shaft, chain case is aluminum and have seen those 40 years old and still in service.
Unless there are needs not apparent your set up should be fine, if it is some high precision machine tool spindle and your looking for next to zero play then there will be trouble.
Dan
 
A lot of bearings are set up as you did it, rotating member (shaft) solid fit and stationary mount can float. I've seen this set up many times in machinery design, automotive timken wheel bearings were always that way and many out lasted the car. Harley transmission main shaft support bearing slides into the chain case housing and is installed with loctite on the shaft, chain case is aluminum and have seen those 40 years old and still in service.
Unless there are needs not apparent your set up should be fine, if it is some high precision machine tool spindle and your looking for next to zero play then there will be trouble.
Dan

Thanks for the input. Play is not an issue. The difference may be that the installation is dry. There is no oil or grease present in the housing. The examples you listed are typically bathed in oil or grease. I am concerned that a spinning bearing would quickly wear the aluminum.
 
What's the pressure angle of your gearset ?

Not sure that I fully understand your question. All gears are flat cut and installed parallel. The gear backlash is about .002 - .003", so the only pressure is from one gear tooth pushing flat against the adjoining tooth.
 
Not sure that I fully understand your question. All gears are flat cut and installed parallel. The gear backlash is about .002 - .003", so the only pressure is from one gear tooth pushing flat against the adjoining tooth.

They don't "push the flat"

There is a "pressure angle" and that angle will create a force
vector of the 2 gears trying to be driven apart.

One of the members more versed in gears should be along shortly
to clarify it better than I can.
 
Hello everyone, my first post.
Look up Limits, Fits and Tolerances on Google or contact your bearing manufacturer, in your situation you require an interference fit on both the outer and inner bearing races, the rolling elements (balls) are there to rotate and take the load radially and axially. Tolerances change with diameter size, if heat is involved or the shaft is mounted vertically you may require C3 bearings. As you have stated that there is clearance on the outside diameter you could simply put a wave washer in behind the bearings to stop them from spinning (defeats the purpose of having bearings if the outer and inner bearing races spin) or as already mentioned, use a low grade Loctite product.
HTH,
Jacko.
 
Not sure that I fully understand your question. All gears are flat cut and installed parallel. The gear backlash is about .002 - .003", so the only pressure is from one gear tooth pushing flat against the adjoining tooth.

The point is that most if not all gear trains do produce a side load, so there will be some side load present.
 
The clearance specified on the OD prevents allows for thermal expansion of the shaft or housing without exceeding the axial load capacity of the bearing. You should have at least one of the bearings free to move axially in its housing. Most radial ball bearings like to have some axial preload for best life. It keeps the load path consistent and prevents the skidding of the balls. A wave spring on one side can provide the needed preload, and also prevent excessive outer race rotation. For internally preloaded bearings (duplex pairs for ex.) you can use an O-ring in a groove in the housing to provide for antirotation.
 
Not sure that I fully understand your question. All gears are flat cut and installed parallel. The gear backlash is about .002 - .003", so the only pressure is from one gear tooth pushing flat against the adjoining tooth.

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