Centering aid for polygonal stock

[mklotz]

Hi mklotz
Please forgive me if I am missing something here, but why clock a piece of hexagon bar in a 4-jaw chuck? Normally hexagon is used for making nuts and bolts and alike, so why use a four jaw when a 3-jaw self-centring chuck will hold on the flats of the bar and run true. I can understand, if a four jaw is the only chuck you have. Just interested as I have never seen this before and it seems a lot of effort to get a piece of hexagon to run true/concentric.
Thank you again for the posts you upload they are always interesting.

The explanation is much simpler than one might expect.

The original picture showed a piece of square stock held in a V-block. During the recent PhotoSuckIt screw-up, that picture disappeared and I was forced to take a new photo to replace it. The original square chunk of metal had been used for a project and I was deeply immersed in the bookkeeping of restoring all my photos so I simply grabbed the first piece of polygonal stock that would present an edge to demonstrate the action of the flapper.

Yes, I would normally put hex stock in the 3jaw although one of my 4jaws is massive and a real beast to get on and off the lathe so I have used it for what would have been 3jaw jobs simply because I was too lazy to remove it.