Originally posted by Paul in OKC
<br />The main thing is that the stock center doesn't have a 60 degree taper on the end, while your mandrel has a 60 degree 'socket'. The stock center point bottoms out before the taper seats in the mandrel. I have always used the stock center (6-7 years now at least) and what I do is to knock the point off the factory tip a bit. Lets the center seat into the mandrel.
What happens in many cases is the tip of the live center gets buggered up sooner or later and won't seat in the mandrel "socket" exactly centered and will cause an "out-of-round" turning....or at least that is the theory.
Actually it is a little more complicated than Paul suggests and I prefer to use the 60° live center; but if his system has worked for 7 years, I can't really argue with success. This is a little difficult to describe and requires your visualizing some solid geometry. Hope I can do this without confusing you. It is assumed that the centering hole in the end of the mandrel has a standard 60° taper, although I have never seen that assumption actually verified. If you stick a 60° cone(the live center) into a 60° hole(the end of the mandrel), the contact surface is a "flat," truncated cone-shaped surface whereas if you use the original LC tip(which is around 30°) the contact area is just the very tip of the LC point.....a much smaller contact surface. Now, if you grind off the tip like Paul suggests,(assuming you don't mess up and grind off too much) the contact area is no longer a point; but is now a circle. Better than a point but not nearly as good as the truncated cone. No matter how much of the tip you grind off, you will never get a proper fit of the live center and the mandrel if the taper angles are not the same. It would be sort of like trying to use a #1 Morse taper tool in your #2 Morse taper JET spindle.
Unfortunately, this business of using a 60° live center is not something that is intuitively obvious to most turners and it doesn't get mentioned in most books or pen turning instructional tapes and DVDs. Changing to a 60° live center may solve your problem or it may not. There are probably a dozen or more common problems that can cause "out-of-round turning and more and a few uncommon ones. Sooner or later you will certainly figure it out; but the process can be frustrating until it is resolved.
I wish you luck!!