Turning a ring

[Lykle]

Hello good people,

After quite a while just reading, I am looking for some help again.

I want to turn a rind on the lathe.
It is like an O-ring of about 60mm diameter and a "wire" thickness of 12mm.
I will make it from Aluminium.

Now how do I make this?

I was thinking of making two clamping jigs, one for the inside while I turn the outside and one for the outside while I turn the inside.

And use a formed tool to do the cutting.
But this does not look totally realistic. The cutter cannot be much more than a quarter of the circumference (of the 12mm) but I still expect a lot of judder.

Any brilliant ideas?

If I mount it eccentric, I might use my ball turner to make the ring smooth?

Any help would be appreciated.

Kind regards
Lykle

 

[gbritnell]

Turn the front half of the ring, inside and out. Now make a plunge cut to a little below the radius and to the thickness of the ring. Now you can get into the backside to turn the other half of the outer radius. At this point you will have the outside finished and 1/2 of the inside. Now cut the ring off.
Take a piece of round stock and drill it out to the I.D. of the ring. Counterbore it to the O.D. of the ring. Now before you take it out of the chuck make a mark on the stock (magic marker) that lines up with one of the jaws on your chuck. Now take the stock out of the lathe and cut through it with a saw to make a disposable split collet. Stay 60 degrees away from your mark. Now put the round stock back in the lathe and line up the mark with the appropriate jaw. Insert your ring and finish turning the inside radius. The reason for making the mark is because the stock will re-register correctly making the counterbore concentric with the spindle.
gbritnell

 

[rkepler]

You could make a form tool that just does the front half rounding then do the inside gripping in a collet or 6-jaw, flip it around and do the other inside; For the outside you can grip on a mandrel or expanding collet and repeat in reverse on the back. Doing it in 4 passes would reduce the chatter.

 

[desbromilow]

When I was making Titanium wedding rings, I'd turn the ID as a cylinder and the OD as a cylinder, then finish turn the ID surface, and then put the ring on an expanding mandrel (made of delrin so it didn't mark the ID surfaces) and then finish turn the OD surfaces.

I don't know if it would be as reliable for a form tool, but if I was single point cutting (using a radius turning attachment) I would have no problem trusting a similar setup in aluminium.

HTH,
Des

 

[Lykle]

Hello Guys,

Thanks for all the practical advice and ideas.
It is clear that I will need to build some tooling to do this right and repeatable.

I was thinking of starting off with a ring with a square "wire" and then trim it to a smooth round wire one.
But maybe I should use a cylinder as suggested and cut it from that.

Also, because I want to be able to do this again, maybe with different diameters etc, I think I will design a specific single point tool holder that will swing around, like a ball turner. Then I don't have to worry about form tools or chatter.

My Ball turner is an "Over the Top" one, so I can't use that. I will use something like the one Steve Bedair did.

Another little problem I have is the fact that it is not 1 material. It is a combination that is glued together. So I don't want to use an expanding mandrel, afraid that I might split it. So turning the outside completely first and then cutting it off and doing the last bit and the inside sounds like a very good idea.

OK, back to the drawing board.

Once again, thank you guys, you have clearly marked my path for me.

Lykle