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cycleclinic-
How can you measure erd to 0.2mm
Clamp the rim to the 28" face plate on your big lathe and check the runout with a dial indicator. You could easily measure polar coordinates to within 0.05mm and plot the circularity without even having to get it centred properly. Obviously a CMM would be better, but not everybody has one of those, at least not in the size required.
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Home-made ERD measuring tool featuring a digital caliper. It's repeatably accurate to less than 0.1mm if you're careful using it . Not normally a particularly useful ability, I'll admit, but if a thing's worth doing it's worth overdoing.
gbj_tester
Brommers
Oh well, I've got them now so I'll see how they build up. They seem pretty round from my ERD measurements - within 0.2mm. They're going on a winter hack anyway, so I'm sure they'll do the job.