Within the course of a few days I've come across two seperate queries regarding turning square stock into PERFECTLY round by using a router on the standard lathe. A while ago (I won't admit how long) I started making this jig with the intention of routing flutes on some of my projects. The steel bar on the bottom is a perfect fit between the ways and the whole assembly slides freely. The outer box gives plenty of course height adjustment whilst the plunge router plenty of fine adjustment. An opening in the rear to allow the tailstock to protrude into the box will no doubt be necessary.