It's fun to use hand tools to get results similar to those from big expensive tools. I'll share with you how to use a grinder to clean up a bicycle bottom bracket.
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Since the grinder is spinning the part, why does it still take off metal? The trick is to use the part of the wheel that is going pretty much down, so the grinding surface is striking at an angle. Don't use the edge of the wheel that will just spin the part; you'll reach plaid-speed in no time flat. Or pucker-speed. Or whatever means just too darn fast.
There are all sorts of tricks and tips to home bike building that avoid the use of complex jigs and expensive equipment. This bottom bracket is all cleaned up and ready for me to weld it in to the current project bike!