Brake drum skimming

[worntorn]

Sticking the self-adhesive abrasive pads on the brake drum surface to radius the shoes works well, but sticking the pads to the shoes to cure brake drum ovality or warping sounds dubious.
It would some abrasive to remove 10 thou+ of work-hardened cast iron..

That's would be an assumption.

I've done this on 3 machines now, the worst of which was my A10. It was almost unrideable, the pulsation was so severe. If I recall correctly, it measured 7 thou out of round.
Took an hour or two to correct the drum. There is lots of mechanical advantage to work with. Almost too much going the other way on the linings. That only takes minutes.

Glen

[berger]

did the emery trick on my back brake that was non existent because the lever is only short compared to a std lever. did  the shoes and drum and now have a brake that can lock the back wheel ---- if I put my big heavy boots on.

[Rex]

That's would be an assumption.

Glen

If I'd known that I could whack  seven thou off a piece of cast iron so easily I wouldn't bother with so many lathe tools, but just keep a stock of this modern abrasive paper to hand.
My existing rolls of emery cloth in various grades don't alter the work piece dimensionally to any appreciable degree.

[worntorn]

The reason the Emery works for this is due to the mechanical advantage available with both the wheel for rotation and clamped brake arm /cam for pressure.
It's quite a different thing than just rubbing some emery over some metal, or even doing so in a lathe.
I wouldn't advise selling your machine tools and investing the proceeds in abrasive rolls.
I still use my lathes and mill for lots of things, just not this. 
If it was much more than 7 thou I would likely use the mill as it's large enough to leave the tire on a 20" wheel and still reach the drum face. With the lathe I have to take the tire off and then remount, plus jig up.
 It's quicker just to use the Emery if the out of round is a just few thou or so. More importantly, the end result is a perfect brake with the absolute minimum amount of material removed from the drum.
You can feel when all comes smooth.

Glen

[Butch (cb)]

Gonna try it on the front of my SP370 anyway.

[Rex]

I finally found a reasonably local person to skim the A7 front drum. He has an industrial-standard workshop in the grounds of his house, complete with lathes, milling machine etc and the remnants of his days building (and sponsoring) race bikes, namely a couple of semi-built Goldie engines, self-built frames etc.
He trued the drum in less than 30 minutes (we went to the local cafe for a cuppa while he did it)  on the biggest lathe using a roller on the tyre to spin the wheel. Sadly through age he's now selling his equipment and taking it easy, and won't be doing many/any more wheels, so I got in just in time.
Shame that, not too many old-style machine shops who have an understanding of bikes still left now.
 

[Jules]

I agree Rex, I did the same a few years ago with the worn headstock on my frame, found a guy with a machine shop in his backyard about 2 hrs away in a country town. Dropped the frame with him in the morning then we had an explore and lunch in town, went back at the end of the day and picked up the frame and drove home..  ...again he was "retired" with a restored Goldie, but was about to shut it all down to look after his wife  ...