Spindle eccentricity ?
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Posted by: Dave B ® 03/11/2006, 01:23:33 Author Profile eMail author Edit

I hope someone with automotive experience can help. I am building a car using a complete BMW 635 drive train.The purpose is to keep the originally designed brake system intact. Because of structure and space limitations I am converting the front McPhearson strut spindles by cutting the strut tube and fitting ball joints top and bottom via adapters. My quandry is this: Upon measuring the spindle diameter where the front outer bearing rides, I found an eccentricity of .0013". Is this an acceptable deviation from round ? Or is it now just a door stop ? Consider, too, that the engine is capable of sustaining 140 mph ( 'continuous running of 6,000 rpm allowable' according to the driver's manual ) ?

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Re: Spindle eccentricity ?
Re: Spindle eccentricity ? -- Dave B	Post Reply	Top of thread	Forum

Posted by: Kelly_Bramble ® 03/11/2006, 09:46:31 Author Profile eMail author Edit

.0013" divided by two is .00065" extra material on each side extra material relative to the axis. The diameter of the spindle, operating load, and rotational velocity will drive your tolerance reqiurements. If I assume you need a ABEC tolerance of 7 (loose), then for a spindle the bearing will have an ID of +.0000 / - .0010. This is a worst case out of roundness (eccentricity)of .001. So, you want your spindle to be approximately as good as your bearing. so, no your spindle is too far aout of round. Keep in mind that your spindle only needs a .0010 roundness at the bearing contact location. Let me put a disclaimer on this, I would determine the original roundness or cylindricity requirements from the maufacturer or local machine shop for that particular original application. It may be higher and your roundness be acceptable.

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