Lathe and concave/bal lturning

[GeorgeD]

Whilst eating my breakfast was watching this clip of an ingenious method of turning a concave or radius,quite uniuqe,as I watched it a second time it suddenly dawned on me...Why make a platform for this turning action? all we have to do is remove the position pin from below the toolpost put a smooth washer on the toolposts spindle,put toolpost back in place but leaving the locking lever loose,fit a square piece of rod in the right hand side and sticking out towards yourself,put a toolin the lefthand side of the toolpost as per normal and the same action can be replicated in the vid.

Simple no?

[irving2008]

Conceptually maybe, but leaving the locking lever loose will give rise to chatter as the hole in the toolpost is not a good fit on the spindle. Also the standard toolpost doesnt put the tool diametrically aligned with the centre of rotation and adjusting the tool length to change the cut radius will be a PITA.

[GeorgeD]

I'll give it a try,Irving...if itworks bad?then I'll make one like that in the vid.

Quite a nifty piece of tooling in my mind.

[John S]

This is known as the Steve BEDair design from the original maker ? although that's probably lost in time.
I dare say if you rear a 1900's engineering book you will see similar.
The point is many have made this and it seems a lot of work and setup, removing compound etc to do a ball.

Look at these setups



Simple cheap boring head fitted to a parallel shank that runs in some form of holder that fits the toolpost. easy to fit and use and accurate in setting.

Another type is the swing type, this is one sold by Arceurotrade for the mini lathe but this one had a simple bracket to allow it to fit many different lathes.



Possibly more limited in use but even simpler to make and use.

I have one that fits my CVA toolroom lathe, a lot like the Bedair design but micro feed, hight adjustment, BBC2 and satellite. Used it once, took ages to setup and it's now in the back of the cupboard.

For 90% of mu work i use the ARC one, the other 10% is done on the CNC.

[GeorgeD]

It wasn't somuch the ball turning that interested me but the concaving method.

I suppose this would take some getting used to as its a two handed advancing of the tool,I was looking to turn pully style beaings on the lathe for running along a round rail.

[irving2008]

Then, depending on the radius, you need a form tool, tho a 60deg threading tool to make a v-shaped pulley would do a perfectly good job...

[GeorgeD]

Hi Irving.

Already made a v-wedge pully for a motorI had,will get some batteries for camera tomorrow and post a pic.

Its as you first said half the radius of a given diameter is what I'm trying to achieve so that the pully sits on the rail like a glove fit.

[irving2008]

Hi Irving.

Already made a v-wedge pully for a motorI had,will get some batteries for camera tomorrow and post a pic.

Its as you first said half the radius of a given diameter is what I'm trying to achieve so that the pully sits on the rail like a glove fit.

Which unless perfect will either increase friction significantly or will be sloppy in the transverse. A v-shape is easier to achieve, provides a point contact which is the lowest friction, and is self-centering.