Centering aid for polygonal stock

[thehomeengineer]

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 Home Engineer