This is not between a dog and the vet, someone explained that say the spindle turns enough for the roller to turn one circumference, fine we have used that distance on the outer ring and it will take a number of revs of the spindle to have the roller to travel one rev of the outer ring, that is like the spindle in an electric motor or a crankshaft.
What happens when the spindle is fixed and the outer ring turns, move one circumference of the roller but this is less than one rev of the roller on the spindle, something must skid and not roll, that is like a wheel.
Will some genius explain why wheels work except when the bearing is drawn on paper, I can’t explain it to the lad who is asking because his geometry says ‘no’.
Thought I was cleaver but it stopped me!
It’s magic! Just leave it at that and get some rest. I accepted long ago that certain concepts are simply beyond me or make my brain hurt! Peace!
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Mechanical engineer here. I could probably answer your question if I understood it! There is no skidding in bearings under any conditions (unless they’re dead). It doesn’t matter whether one race is fixed and one rotating, its exactly the same as both rotating.
Bearings intended for full rotation can be different to those for part rotation. Full rotation bearings often have a cage to space the balls or rollers to reduce friction and allow more lubrication. Part turn bearings have no cage but extra balls (full compliment) to fill the bearing. This spreads load transfer and reduces wear.
Bearings definitely work (unless fitted without grease).
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Learn something every day.. sometimes! It’s still ‘magic’ to me though!
Glad somebody understands that stuff though.
It’s the geometry that says different, draw two circles, inner and outer race with a roller between. Put a line through the centres, mark off the distance round the outer circle equivalent to the circumference of the roller. This is the distance the outer moves to rotate the roller one revolution. Draw a line from the centre to this point, where it bisects the inner the distance back to the start point is less than the circumference of the roller, simple geometry, therefore, the roller has to skid. Can’t argue with the lad and can’t explain why bearings work when the outer is is the mover. It’s like the old steam engines without a differential, a pin was pulled out of one wheel to go round a corner because the inner and outer radius differed, if they were locked one had to skid.
Sadly I have been chastised by the political correctness police for my reference to a naughty word in my first post, doesn’t matter that it was camouflaged with letters missing. Sorry if I offended anyone but I would advise not watching Clarksons Farm! Difficult to know right from wrong nowadays.
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It is not about political correctness but it is about you abiding by the rules of the forum which you agreed to when you joined. Disguising a word does not remove it.
Please remember that this is not only a one make motorcycle forum but also a window to the world for our club. Try and keep your posts on topic please.
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You’re thinking about it in a strange way. The difference between circumferences is irrelevent to this, you don’t need all three parts to fully rotate at the same rate. Why is it different to a roller acting between two flat bars? It isn’t is it?
Whether the outer is moving and the inner static or the opposite or both is irrelevent. The relative motions are the same.
Sorry, straighten the two races into flat bars, one moves more than the other, what happens to the roller, it skids!
The lad is right, rotate inner race and the roller never catches up on the outer, the opposite, rotate the outer and using your flat bars, one is longer than the other, doesn’t work.
Still can’t explain it!
Sorry Shifty, Steve is correct. There is no skidding between any of the components, that is why they are called frictionless bearings. There is a rolling element between the two races. If you, and your lad can imagine cutting through the inner and outer races and straightening them out you will have two flat bars. One will be longer than the other, obviously. Now put a ball or roller between the two and move one bar relative to the other. What happens? The roller rotates and the bars move in relation each other. It doesn’t matter which bar you move the effect is the same. Obviously the ball or roller will reach the end of the shorter bar ( inner race) before it reaches the end of the longer bar (outer race). I think this maybe what is confusing you both. In the example I’ve given the ball or roller will need an extra length of bar to keep rolling. In the case of a bearing the roller will start to travel on a second revolution of the inner race before it has done one revolution of the outer race. Maybe set up some practical experiments and it will all become clear. I hope this helps, Phil
Exactly, your last sentence says it all, if you put stops on the end of the bars and move the longe, that is, outer race, the roller hits the stop on the shorter bar first, inner race, and something skids, try it, two pieces of wood and a bottle, I have and it skids.
Move the shorter, inside race length, no problem.
but bearings don’t have a stop, they are continuous circular rotation?
Think of the inner and outer races as bars of infinite length, thats effectively what they are.
If there were any skidding in bearings, that would defeat the entire purpose of them. They are capable of operating at incredibly high rpm, ive designed them in to machines running at 20,000 rpm on production lines with reliable success.
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I’ve run machines at 20,00 RPM also but it was the inner rotating not the outer, this works fine.
It makes no difference which is rotating. The relative motion of the two is exactly the same so the mechanics are the same.
The mechanics may work to a degree but the lads geometry lesson proves it doesn’t work, the mechanics say the inner must be the driver so the bike rotates round the wheel and this is the effect that might look like it’s okay but this is maybe say 99.9% of the time. The dominant driver must be the inner even when the outer revolves.
Question why a crank can do hundreds of thousands of miles at elevated revs but during that time wheel bearings will need changing a few times, they skid a little!
Crank shafts are generally on a plain bearing with constant lubrication from routinely replaced lubricant and in the crank cases. Wheel bearings are ball bearings which are sealed for life with a small quantity of grease. Eventually grit and moisture get past the seals and causes bearing failure. Wheels are also subject to shock loading and loads in multiple directions. Thats why they fail much quicker than crank bearings.
Something is wrong with your geometry. You are coming up with something that is contrary to very well understood engineering principles that I can assure you are not wrong. These are the basic principles that all engineering is based on and has been understood for hundreds of years and companies like NSK and SKF base all of their designs on them and if they were wrong, they’d have been sued out of existence decades ago.
Sorry you do not understand basic geometry, go Bach to my instructions and draw the two circles with a roller between, mark the circumference length of the roller round each circle and you will see the roller cannot roll round both at the same time, the lad is correct , his maths teacher is teaching basics as old as Pythagoras. My original question was how to explain the bearing when the geometry says it doesn’t work, no one has answered this yet.
My old bike has roller crankshaft bearings and a separate oil seals but my car has plain bearings, try electric motors if you want long running roller races.
You imply, Shifty, that any given ball stays in place, but it doesn’t. Imagine yourself stamping on an empty beer bottle in a dark garage, what happens? Frictionless movement followed by painful fall… and everything happened as in bearing. There was no friction against the floor, AND no friction against your shoe’s sole. But bottle have moved! So bearing balls/rollers do!
I do not imply the ball is stationary, the ball is rolled its circumference driven by whichever ring rotates it but unfortunately the two rings have a different diameter, therefore, a different circumference , if the inner is the driver the ball or roller never catches up because of the greater circumference of the outer, but tell me what happens when the outer is the driver and has rotated the ball one circumference or revolution, this distance does not exist on the inner, what happens?
It doesn’t matter what the inner and outer circumferences are, the outer one has a radius that is greater than the inner one by the bearing diameter, only one of them moves and the bearings move. The inner and outer do not move together in sinc. one is fixed and the other moves around it or within it.
The distance the moving part travels is the circumference of the bearing per bearing revolution, the distance the fixed part moves is zero.
I hope this explains your connumderum.
Best wishes Chris