Struggling to squeeze my balls hard enough

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

If you can get the 1" steel ball red hot for a couple of minutes it may soften it enough to let you drill it

Roy

Fully in the style of the thread title, can I suggest that a set of blue balls might assist. Scribble marker pen over your ball and then clamp up. Where chafing occurs, that will indicate the line of contact and guide you where attention can best be focussed

Looking at the album, could the pillar/piece of metal on the other side of the clamping screw be too long? If it is over long, and ridgidly connected to the clamping plate, turning the screw will just be trying to bend that plate rather than squeezing the ball. Maybe remove the capscrews holding those parts together, mill a semi-circular or vee groove in both and use a round rod as a pivot.

Break through the steel ball surface with a carbide tipped drill, or grind a flat to drill through

Edited By Ady1 on 20/09/2023 19:41:52

It is best not to try and create a full concave recess that closely matches the ball surface, rather make a recess where most of the central area is relieved so the the ball is gripped just by an annular ring at the largest possible (for that size) ball diameter.

IanP

You could let the ball down by heating to red heat and covering in insulting material to let it cool slowly then you can work on it. For the female make internal form tool. For a perfect match run them together with a little abrasive paste.

+1 for what Ian P says.

Grip it between two fairly narrow rings with tapered insides. Probably aranging to work at something like 1/3 rd of the diameter off set from top and bottom would be fine.

All the successful ball based tilt holders I've used seemed to grip on narrow rings.

Clive

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

And re DV31k's comment re "Looking at the album, could the pillar/piece of metal on the other side of the clamping screw be too long? If it is over long, and ridgidly connected to the clamping plate, turning the screw will just be trying to bend that plate rather than squeezing the ball. Maybe remove the capscrews holding those parts together, mill a semi-circular or vee groove in both and use a round rod as a pivot."

Yup - I worried about that too. I'll reduce the length a bit.

I had to drill 3/8" holes in 2" hard steel balls used 2 myford face plates and 3 bolts to hold them together, trapped the ball in the hole in the middle and used a 3/8" carbide tipped drill in the tailstock on an S7. Noel.