Welcome to ModelEngineMaker !If you have problems registering or logging in, please use the contact menu option to request assistance.
It's not brazing---it's silver solder. Those sprockets are sold as just the outer rim and teeth, but no hub. I make my own hubs "to suit" and silver solder them into place. You're right though, it certainly looks like brazing.--Brian
An executive decision has been made. I'm going to make my own pulleys and use o-ring drive belts.