We replace our bellville washers yearly. It's part of the PM program here. It just needs to be done on occasion. They make a tool to check the tension of the springs. Command makes one, a bit pricey though. I found one significantly cheaper somewhere. If I find it I will add it to this post. Of course it's too expensive for us to own one. Spindles are cheap though (sorry I've been surly lately).:boxing:
I take a pry bar and periodically try to leverage the toolholder while in the spindle. I insert the bar between the spindle nose and the flange on the toolholder.This checks for a loose condition before it gets catastrophic. Don't ask me how I finally figured this all out.
Found it; http://www.clamprite.com/productinfo.asp
Don't know anything about it, just ran across it.
Still working in the "D".