I've tried and failed to embed pics on the post but there are a couple in an album…

Too cack handed to grind tools freehand so I cobbled together a rest a la Mr Hall's book. The angles in the cups to secure the plastic ball at the heart of the design approximate to the drawing but no matter how hard I squeeze the table tends to be looser than I'd hoped. It holds but isn't completely bomb proof and probably wouldn't resist the vibration of my cheap bench grinder for long.

Daresay the problem lies in the geometry of the cups I've created for holding the balls and they will need fettling. Just roughen them up? Pock mark them with a centre punch at the risk of chewing the ball up more quickly? I don't have big ball ended mills or the means to work something 1" or so so need a simple solution.

Option in the book is drill and de burr 12mm through hole and rely on what would then be pretty harsh edge contact to grip the ball but Would a properly formed cup be better? Maybe by trapping some coarse emery between a spare ball and spinning it around with a power drill to improve the seating?

I've got a 1" Steel ball from a bearing which would look better but the file bounces off it so it'll be a pig to drill and tap, and more slippery than a plastic ball, but should I consider that?

Any thoughts gratefully received. It's almost a useful tool and was a good exercise to learn new skills so I'd like to get it sussed.

Andrew

Thanks guys. Food for thought.

I'll turn up a couple of the narrow ring type grips and see if that works. I'll also attempt to heat and drill the steel ball as I think that will be more durable in the longer term.

As ever the guidance of this group is much appreciated.

A