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Arthur.Marks
05-22-2012, 02:43 PM
I have a nice french crank for a bicycle that uses cotters to secure the axle. These axles are not the most prevalent to find used. I recently found a couple that might work of sufficient length, and the Post Office plain lost them in transit. While they may arrive in the undetermined future, there is no certainty of that. In the interim, I figured it would be a nice project to, "see if I could do it." The crank profile is simple enough as well as the cotter flats. The bearing races for 1/4" loose ball bearings was my hopeful challenge. i.e. how smooth or rough would the crank feel when completed given my skills. This would also give me needed practice with my toolpost grinder. I intend to use 304 or 316 stainless.

I began measuring my sample spindle of insufficient length to copy the bearing profile. To my initial surprise---it quickly made logical sense---the race profile is not r-1/8". The closest I've matched it to is a surprisingly metric r-4.5mm. The sensical portion of me has determined a race cannot equal the ball bearing's radius because it would then have no room to rotate as it should. Instead, it would sieze. Can anyone point me to a formula used to dictate a simple, straightforward, loose ball bearing race radius given the bearing size? Thank you for any pertinent information you may be able to add as well.

Barrington
05-22-2012, 03:36 PM
I think the relevant term to Google is 'Raceway Curvature' or 'Track Curvature'

e.g. http://www.dynaroll.com/raceway-curvature.asp

Cheers

.

tdmidget
05-22-2012, 04:36 PM
Why would you make a bearing race out of something that cannot be hardened and is famous for galling?

pixelated
05-22-2012, 04:39 PM
This table may help;

http://sheldonbrown.com/velos.html#dimensions

Arthur.Marks
05-22-2012, 04:49 PM
Thanks, Barrington. My axle doesn't seem to match the f figure of 0.56 +/- 0.03. That would work out to be Ri= .133-.148 inches. Using my inch radius gage, I know it is between .1719" and .1875"; although, it probably doesn't matter that much. If I make it a mean radius of .180" it would likely work just fine. I'm not a bearing manufacturer, after all, just some guy with a home shop trying his best ;)

tdmidget: It is just what I have on hand. What would you recommend, 410, 416, 440C or something else? I didn't want to make this a dent in my wallet, and I've never heat treated a SS. All I've got is an Oxy/Acet. torch and a home oven :o