Different inserts ?

[wm460]

A while ago I bought an Vicmarc chuck on E bay it came with the M30 x 3.5 insert on the right, I needed a 1 X 8 TPI. So I bought a genuine Vicmarc insert from CWS, the one on the left.
My questions are why the difference size?
The grub screw, is that to stop the chuck coming off when you reverse the lathe?
Why the difference in the size , weight and construction?

[Tim the Timber Turner]

The first insert is the old style.

The second insert has a grove in it. There is a matching grove on the spindle of the later model Vicmarc lathes. This takes a locking collar which picks up both groves and enables the lathe to be run in reverse without the risk of the chuck coming unscrewed.

This is handy when taking the center out of hollow forms on a longbed lathe. You don't have to lean over the bed of the lathe.

Later Vicmarc lathes have a R/H thread on both inboard and outboard. You don't need any L/H thread chucks or faceplates to turn outboard. Pretty smart thinking by Vicmarc.

Cheers

Tim

[Jim Carroll]

You have hit the nail on the head.

Generally smaller lathes do not have reverse so no locking screw needed.

The large ring around the M30 insert is also used on the vicmarc lathes to hold the chuck in place with their locking ring.

Snap Tim

[wm460]

Thanks Tim and Jim.