tap tap tap... The secret to it is backing the head, and being good enough with a hammer to have the tip of the ballpeen hit where you want it to. It's more like hammering than tapping. Wifey came out to the shop to see what the hell was going on. Some of the guys have used an airhammer. Anyway, the idea is that you beat down and roll over the end 'till it cinches up tight. It's more of a feel. Once you get it you got it...really pretty easy. Steel is definitely a lot tougher than brass or bronze. I once built a clinker planked skiff that had the plank lands riveted together with copper rivets. On that you could hear when they were getting tight.