As it usually goes, I was recently 90% done on a project and my grinder (4.5" hitachi) wasn't spinning like it normally does.  One of the brushes on the motor had failed.  The copper wire/brass disk connection had failed and you could see heat marks on the copper wire.  So I cut out a copper disk from some scrap, and carefully melted a blob of silicon bronze onto the center of the disk.  Then I let it cool, and then carefully got the blob molten and stabbed the copper wire into it and let off the pedal, freezing the wire in place.  I think I was running around 45 amps with a .040" tungsten.  The grinder works great, and the customer got their work, and I got paid.