Hi manualmillandlathe:
As others have pointed out, you will have a very hard time trying to turn something so long, skinny and floppy between centers.
My personal GOTO for getting around this is to do a variant of what cole2534 advocates in post #5 and that is to turn it in sections.
I have had best success on parts in this size range and in this material by using a 6 jaw Set Tru chuck at the headstock end and a live center in the tailstock.
I've been less successful with a 5C collet chuck because stock Delrin bars are often just enough oversized to make them a PITA to try to advance through a collet.
So I stick out maybe 2" at a time...I clock the stock before I begin and get it running as close as the chuck will run...typically better than 0.0005" TIR.
I put in a center before I turn the first 2" end.
I mark the periphery with a Sharpie stripe that I align to the same jaw as I incrementally advance the stock and I put a live center against the free end.
I mark and tighten only the same pinion on the chuck with each clamping, so the scroll will always shift the same way when I tighten it, and I keep the clamping forces light...in other words I don't reef the piss out of the chuck.
When I set the live center I turn on the lathe and then just advance the tailstock barrel until the center starts to rotate...squashing the snot out of the center makes the part inchworm as soon as you stick it out of the chuck much more than 5 diameters or so, so it becomes impossible to hold size and concentricity.
It sounds elaborate but it's mostly how you finesse the process details.
Speaking of which, I use a tool with a small nose radius and dead sharp with positive rake.
Inserts meant for aluminum work well...so does hand ground and stoned HSS.
Typical turning inserts for steel don't work for shit.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
