MB33

I have a front hub with some light pitting on the bearing surface area of both cones. I see posts on here about people using a lathe and a special bit to get rid of the pitting. Has anyone done this by chucking the cone in a hand drill and using sandpaper? I would think it would work. I have every grade of sandpaper under the sun up to 2000 grit, Simichrome, and 4 grades of steel wool, I'm just not sure what grades of to start and end with.
Any tips would be greatly appreciated.

fietsbob

More than sandpaper.... (have you tried your Idea yet, how did it work ?)

how it has been done ... 2 drill motors 1 has a cone shaped, grindstone bit, the other spins the cone on an axle..

don't let the heat of doing it take the temper out of the steel .. keep or cool, dipped in water often

noglider 

I don't think this is practical. Good cones are hardened very hard. If you make any progress at all, it will be with huge amounts of materials and labor, and they would exceed the cost of replacement cones. And you might not get anywhere. Or if you get somewhere, you might go through the hardened layer and end up with a soft outer layer, and that's no good. I have never heard of anyone succeeding at this, though I've heard the idea over the years.

dabac

noglider 

OK now I've heard of one person succeeding at it. I'm glad to know I'm wrong.

dedhed

https://www.hemmings.com/magazine/hs...e/1282111.html

https://www.brownells.com/gunsmith-t...prod27119.aspx

Velo Mule

With only light pitting the technique that i use is to clean out the race of any grease and debris, clean the bearings and cone. Then repack the race with lapping compound. Re-assemble with the old ball bearings, assuming they were good. Then connect a drill motor to the axle and hold onto the hub. Run the drill for a few minutes in both forward and reverse. Then dis-assemble and throw away the ball bearings. Clean everything real good and re-assemble with new ball bearings.

The technique described in the original post would be for for more serious pitting. I don't see why it wouldn't work, This diameter of the grinding tool must be real close to the diameter of the balls. It might be good to follow up with the lapping compound afterward.

Let us know how it goes. With pictures please.

randyjawa 

I won't say that you are wrong, noglider. Simply put, the cones and the cups are case hardened, not completely hardened. With that in mind, once the hardened surface where the balls run, is gone, wear rate will accelerate. Yes, one might get away with it but not forever. Of course, I might be wrong also but, were it me and were I riding a long way away from home, my bearing cups and races will always be in good shape - before heading out.

All that said, I have dressed bearing races and/or cups but only if a proper replacement set, in good shape, was not available at the time. And, I stayed close to home on any such steed. And, I never sold a bicycle with damaged bearings, just in case anyone is wondering.

cinco

I've heard that most are only case-hardened to minimize distortion since they're machined before hardening. The exception to that is classic Campy, which are rumored to be hardened all the way through and machined afterwards. I have no actual evidence of any of that, however.

I've re-cut several Campy cones using a toolpost grinder on a lathe, but can't speak to the relative success of any other method. I tend to avoid messing with cones from other brands except in times of desperation.

MB33

Thanks for the advice so far folks. I'm going to give it a go, but it might be a couple days before I can get my "redneck lathe" set up. My plan is using a 3/16 drill bit for a block, start with 1000, then go to 1500, then 2000 (all with water), then 0000 steel wool with simichrome as the final polish.

eom 

[QUOTE=dedhed;20813017]https://www.hemmings.com/magazine/hs...e/1282111.html

"But the advantages to Cherry Red compound are that it's not a cyanide-based compound"

A good thing, helps with repeat sales.

Headpost

I thought I would bump this old thread:

I came across this page on the web:

https://bicycleobsession.wordpress.c...ted-hub-cones/

And tried the technique with a pair of cones that were only slightly less pitted than the ones shown on the website, using a slightly simplified (and totally low budget dirtbag) setup:



Even so, I was amazed at how well it worked. The only other thing I did was to spin them against this 3M metal polishing cloth I have. I wish I had taken "before" pictures, but they weren't really very old cones, just abused, with some mild pitting. Are they slightly out of round now? Possibly, but the reassembled wheel seems to spin quite smoothly. Not new-wheel-smoothly, but good enough so that, giving the axle the "hand test" now, I wouldn't feel the need to repack the bearings. Anyway, I'm really psyched to know about this, thanks.

WGB

Headpost
Very impressive work!
Perhaps you should add to the "Hints and Tricks" thread on the mechanics forum. Might encourage someone else to try and save an irreplaceable part, especially during covid.

oneclick 

Um, no.

The race surface has a larger radius than that of the balls, but how much larger does not (within limits) matter, except that larger is marginally better [1]

What matters is that that the line between the points of contact on each side of the balls both
a) runs on a hard smooth surface; and
b) is at an angle correct for the kind of load expected. All you have to do is grind so that line is in the same relative position.

[1] Larger is marginally better because the balls do not make a perfect point contact, there is some elastic deformation, and so there is "skidding" of the parts in contact at the edges of the line of contact; this skidding is the source of wear, and a flatter base reduces the width of the line and the resultant wear.