# Strange Shaped Leg



## WESLEYGC (29 Oct 2021)

Hi Guys,

I'm hoping you guys can settle a bet. I'm making a stool that has a very strange shape leg. Its a 40x40x1000 blank and wants to go from dead square at one end to circular at the other. The leg needs to look like this-

















These images show a section all the way up the leg from top to bottom. Each face has a radius ranging from 22mm at the bottom and increasing as it moves up the leg to the square end. My question is, can this be done on the lathe? I dont think you can achieve this shape and on the lathe you'd get something more like in my next set of images.
















So I think you'd get something like this and you'd lose that elegant changing radius type deal that I show in the first image set. What do you guys think? There is a couple of beers riding on this so I hope you agree with me!

BTW I have done a reasonable amount of spindle turning and a couple of bowls, but I'm looking to learn more and this looks like a great place to do that!


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## Inspector (29 Oct 2021)

I don’t think you can do the first leg on a lathe. CNC maybe because you can make the changing radii. You’ll get the second leg. If you did multi axis or offset turning you’ll get a compromise. Hand working can make the first but doesn’t involve the lathe. Have fun.

Pete


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## WESLEYGC (29 Oct 2021)

Thanks for the response. I agree I think I’ll mark it out and use the trusty no5 . Either that or 5axis cnc. When we tried to visualise it I hadn’t 3d modelled it, so that made it much clearer Option A wasn’t achievable on the lathe!


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## Paul Hannaby (30 Oct 2021)

Yes you can do it on the lathe, it's called therming and would entail turning on multiple axes using a therming "jig".


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## Adam Pinson (30 Oct 2021)

WESLEYGC said:


> Hi Guys,
> 
> I'm hoping you guys can settle a bet. I'm making a stool that has a very strange shape leg. Its a 40x40x1000 blank and wants to go from dead square at one end to circular at the other. The leg needs to look like this-
> 
> ...


Witchcraft


WESLEYGC said:


> Hi Guys,
> 
> I'm hoping you guys can settle a bet. I'm making a stool that has a very strange shape leg. Its a 40x40x1000 blank and wants to go from dead square at one end to circular at the other. The leg needs to look like this-
> 
> ...


Wouldn't you just mount it as a spindle, turn the round end to the desired diameter and taper out the cut towards the square end?


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## Inspector (30 Oct 2021)

Adam Pinson said:


> Wouldn't you just mount it as a spindle, turn the round end to the desired diameter and taper out the cut towards the square end?



That would give you the second example the OP gave. He wants the first.

Pete


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## Adam Pinson (30 Oct 2021)

Inspector said:


> That would give you the second example the OP gave. He wants the first.
> 
> Pete


I need to look again, that's what happens at 4 in the morning !


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## Sporky McGuffin (30 Oct 2021)

Also in the first one the centre of the curve isn't in the centre of the leg, so no, not on a normal lathe.


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## Sporky McGuffin (30 Oct 2021)

Paul Hannaby said:


> Yes you can do it on the lathe, it's called therming and would entail turning on multiple axes using a therming "jig".



I sit corrected - just looked it up. Complicated but ingenious.


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## Lefley (30 Oct 2021)

Art liestman does a lot of therming jig turning. It would not work. On a therming jig you would always get an arc on the top of the spindle not a perfect square like your first picture shows, and also the end of leg where picture is a true circle you would also end up with 4 arcs not a sphere.a therming jig would give you the second picture. But also the top would be closer to square but still be like the bottom of leg.


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## WESLEYGC (30 Oct 2021)

Paul Hannaby said:


> Yes you can do it on the lathe, it's called therming and would entail turning on multiple axes using a therming "jig".





Lefley said:


> Art liestman does a lot of therming jig turning. It would not work. On a therming jig you would always get an arc on the top of the spindle not a perfect square like your first picture shows, and also the end of leg where picture is a true circle you would also end up with 4 arcs not a sphere.a therming jig would give you the second picture. But also the top would be closer to square but still be like the bottom of leg.


This sounds very interesting even if not applicable to my current project. Do you have any useful links to therming related content?


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## gregmcateer (30 Oct 2021)

Lefley said:


> Art liestman does a lot of therming jig turning. It would not work. On a therming jig you would always get an arc on the top of the spindle not a perfect square like your first picture shows, and also the end of leg where picture is a true circle you would also end up with 4 arcs not a sphere.a therming jig would give you the second picture. But also the top would be closer to square but still be like the bottom of leg.



I am utterly inexperienced at therming, but I think Paul is right that it could be done - would it not be possible to achieve it if the blank is offset in the therming jig, so the required square section isn't touched during the turning?

More than happy to be shot down on this one, of course


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## Lefley (30 Oct 2021)

WESLEYGC said:


> This sounds very interesting even if not applicable to my current project. Do you have any useful links to therming related content?


I started private conversation with therming info. Here is a picture of a therming jig. The idea of a therming jig is you turn more than one piece at a time to keep the balance, as you are only turning one side of the item at a time. then rotate a quarter turn and keep turning until you have turned all four sides.


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## peter-harrison (3 Nov 2021)

The reason why you can't do it on a lathe is that the radius at the top of the leg is infinite, it being flat.
I would suggest turning the bottom inch or so on the lathe, to get it circular and centred, and then doing the rest by eye with a hand plane.


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## Sandyn (3 Nov 2021)

I made legs vaguely like these. Not quite round at the bottom. It was about 35 years ago, so I can't remember for sure what I used. I think I planed it to the rough shape then finished off with a hand held belt sander. I took off all the square edges.






The first image made me think of this.


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## Lefley (4 Nov 2021)

Sandyn said:


> I made legs vaguely like these. Not quite round at the bottom. It was about 35 years ago, so I can't remember for sure what I used. I think I planed it to the rough shape then finished off with a hand held belt sander. I took off all the square edges.
> 
> View attachment 121180
> 
> ...


You’re so right. The first image is exactly that. Unattainable.


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