Same as Clive, not totally convinced about clamping tool like that but top marks for the flywheel effect of the chuck.

I’d be concerned about the cutter being flung out too. A bit of round bar with an angled slot milled in it and two or 3 set  screws would not be hard to make and more secure.

Robert.

For the 40 plus years I have been model engineering I have regularly seen that method suggested as a way to hold work in the lathe so don’t see any more risk of a tool flying out as there would be with a workpiece. Many here seem to suggest Spary’s book to beginners and he was up for using that method.

Used that method to grip work a few times myself

As for plastic gears I’m inclined to think the opposite. A lightweight flycutter will stop and start as the tool enters and leaves the cut which loads and unloads the gears. As mentioned by others the innertia in the heavy chuck will go some way to damping out that stop start load.

The, very experienced, machinist who introduced me to such canter wise clamping of square or rectangular stock in three jaw chuck was adamant that the material should sit back tight against the chuck body and not project more than the external jaw depth. He said that if that advice was not religiously followed it was certain that a workpiece would self eject sooner or later.

He considered this an undesirable occurrence.

I guess it’s like so many things. You can push the envelope a bit if you know what you are doing and take appropriate care in setting up. Going in all gang ho and willy nilly is asking for trouble. Which may, or may not, ever find you.

For sure its easier to get a secure, well aligned hold when the chuck is in the lathe with a secure base to work against than when its pointing down on a mill spindle or just a loose chuck and arbor.

I’ve only every used the idea for squaring up smallish material or sorting out rodent nibble quality cuts on an end. Always gone fine for me but I made sure to take that extra bit of care setting up and verify tightness after the first three or four cuts. Whether or not I ever encountered things actually working loose has long faded from memory. For sure I’ve never used the technique this century.

Clive

On 9 October 2026 at 13:23 JasonB Said:

For the 40 plus years I have been model engineering I have regularly seen that method suggested as a way to hold work in the lathe so don’t see any more risk of a tool flying out as there would be with a workpiece. Many here seem to suggest Spary’s book to beginners and he was up for using that method.

Used that method to grip work a few times myself

As for plastic gears I’m inclined to think the opposite. A lightweight flycutter will stop and start as the tool enters and leaves the cut which loads and unloads the gears. As mentioned by others the innertia in the heavy chuck will go some way to damping out that stop start load.

I was thinking about the start up not the cut.

A left handed lathe tool would enable normal forward spindle rotation. I would be concerned about the sideways uneven loading on the poor chuck.

My effort on the subject of flycutting was a 20mm lefthanded boring bar with a WNMG08 or WNGT08 insert with a 30mm shank to fit in an R8 to er40 collet.