So far - so good. I've had no problem with either one snapping off. The reduced shaft into the collar is 1/2". You could put a steel ring around the shaft to keep from chewing up the wood but I didn't. I don't tighten it all that tight, just till I feel it bite. It has never come loose during use and has never rattled. It is a fairly good fit through the collar so it doesn't need much to hold it in place. I really like being able to change the sound of the bass by swapping endpins. I turned down about a dozen before I found what I liked.
While your buddy has the lathe running have him turn some hickory for you. It worked better than oak on my bass (yours may be different). I would like to find some osage orange to try, I've heard good things about it.
Good luck, let me know how it turns out.
Jazz is not a list of tunes, it's an attitude.