bowls on a joiners lathe, if that makes sense

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bowls on a joiners lathe, if that makes sense

Postby Follansbee » Mon Apr 19, 2010 3:58 am

It's been a while since I had anything to add to this forum; but here goes. I have been turning bowls lately; mostly my work is furniture. But I got this section of an apple tree that I couldn't resist. I wanted to just try to show some folks that you don't absolutely need a dedicated "bowl" lathe to turn a few bowls. I use this quasi-framed lathe for my spindle turning and sometimes turn bowls on it as well. As a woodworker I used to know once told me, "I didn't know I couldn't do it."

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My tool rest sits on two iron brackets that run through the headstock & poppet of the lathe. the brackets are tightened by wing-nuts, thus gripping the tool rest against the lathe parts. I shim it further out when I am turning bowls. I don't turn really large-diameter bowls; nor very deep. Maybe 4" deep x 10" dia would be the largest I have tackled this way. smaller is easier. I use a mandrel with a turned tenon fitted into a 5/8" hole in the bowl's middle. I think I got this notion from Mike Abbot's book many years ago, then verified by the York archaeology book, I forget what it's called. Some of this was before I knew Robin Wood existed! Then Ned Cooke sent me a postcard of Robin turning a huge nest of beech bowls, and I thought I'd stick to joinery.

here's more shots of the apple bowl today.

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Re: bowls on a joiners lathe, if that makes sense

Postby robin wood » Mon Apr 19, 2010 9:07 am

Nice work Peter and seeing the other pics on your blog you must have your tools sharp and technique very good to get such a clean cut on such gnarly wood. I think it might be worth trying a slightly larger diameter mandrel for a bowl that size.
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Re: bowls on a joiners lathe, if that makes sense

Postby Robin Fawcett » Mon Apr 19, 2010 9:39 am

Follansbee wrote: I wanted to just try to show some folks that you don't absolutely need a dedicated "bowl" lathe to turn a few bowls.


Hear, hear Peter. I've been using my 'ordinary' lathe to turn bowls on for quite a few years and a bowl or spindle gouge instead of a hook tool (for the outside at least).
Is that 10 turns of the cord around the mandrel? - I get away with 3 or 4.
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Re: bowls on a joiners lathe, if that makes sense

Postby Follansbee » Mon Apr 19, 2010 11:45 am

robin wood wrote:Nice work Peter and seeing the other pics on your blog you must have your tools sharp and technique very good to get such a clean cut on such gnarly wood. I think it might be worth trying a slightly larger diameter mandrel for a bowl that size.


Thanks, Robin. What is the function of the mandrel size? I assume I get more revolutions with a small-diameter mandrel - what do I get for increasing its diameter?
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Re: bowls on a joiners lathe, if that makes sense

Postby Follansbee » Mon Apr 19, 2010 12:21 pm

Robin Fawcett wrote:
Follansbee wrote: I wanted to just try to show some folks that you don't absolutely need a dedicated "bowl" lathe to turn a few bowls.


Hear, hear Peter. I've been using my 'ordinary' lathe to turn bowls on for quite a few years and a bowl or spindle gouge instead of a hook tool (for the outside at least).
Is that 10 turns of the cord around the mandrel? - I get away with 3 or 4.


Yes, Robin - I just felt that some folks might be thinking it was not do-able. Once I started using a hook tool, a friend of mine said her chickens liked those shavings the best; (she said they would fight over them, & leave the shavings from spindle work lying around) = so I used to get free fresh eggs in exchange for the hook tool's shavings. she has since moved, and is down to 2 chickens...so the egg-train is slowing down...
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Re: bowls on a joiners lathe, if that makes sense

Postby Spokeshave » Mon Apr 19, 2010 1:37 pm

Thanks Peter! I have been away from the forum for a while with only a distant hope of bowl turning. The last 18 months have been consumed with a job change, 1,000 mile move and a stack of projects to rehab the old house we moved into. I do have my spindle lathe set up and this give me a little hope I may be able to finally use the bowl hook I bought from Robin Wood 2 years ago!

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Re: bowls on a joiners lathe, if that makes sense

Postby robin wood » Mon Apr 19, 2010 5:11 pm

Follansbee wrote:
robin wood wrote:Nice work Peter and seeing the other pics on your blog you must have your tools sharp and technique very good to get such a clean cut on such gnarly wood. I think it might be worth trying a slightly larger diameter mandrel for a bowl that size.


Thanks, Robin. What is the function of the mandrel size? I assume I get more revolutions with a small-diameter mandrel - what do I get for increasing its diameter?


Mandrel size related to bowl size will alter the gearing. At the moment you are in a high gear so it will take quite an effort to set it spinning but then it will be going at high speed (good for getting a good finish) but will also be easy to stop if you start taking heavy cuts. Turning a mandrel maybe 1 1/2 times the diameter of the one you have will make it very easy to spin the bowl back and forth, much more like spindle turning. The speed of the wood at the rim passing through the tool will still be high due the larger diameter of the bowl if that makes sense. Having a larger mandrel will decrease the number of revolutions but I find 2 revs is plenty.
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Re: bowls on a joiners lathe, if that makes sense

Postby arth » Mon Apr 19, 2010 7:14 pm

robin wood wrote:
Mandrel size related to bowl size will alter the gearing. At the moment you are in a high gear so it will take quite an effort to set it spinning but then it will be going at high speed (good for getting a good finish) but will also be easy to stop if you start taking heavy cuts. Turning a mandrel maybe 1 1/2 times the diameter of the one you have will make it very easy to spin the bowl back and forth, much more like spindle turning. The speed of the wood at the rim passing through the tool will still be high due the larger diameter of the bowl if that makes sense. Having a larger mandrel will decrease the number of revolutions but I find 2 revs is plenty.


Currently trying to build a bowl lathe. What would the optimen diameter be for a mandrel?
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Re: bowls on a joiners lathe, if that makes sense

Postby paul atkin » Mon Apr 19, 2010 9:25 pm

start with one around the fifty mm size ish and work on bowls 6-8 inch dia
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Re: bowls on a joiners lathe, if that makes sense

Postby arth » Mon Apr 19, 2010 9:51 pm

Thanks Paul, going to try and make one tomorrow.
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Re: bowls on a joiners lathe, if that makes sense

Postby Steven J » Fri Apr 30, 2010 3:15 am

Peter,

Thanks for the encouragement to give it a go. I am building a new workshop and one of my first projects planned is a lathe. Your photos are great and really make is so much more enjoyable to view this post. Thanks.

Steve
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Re: bowls on a joiners lathe, if that makes sense

Postby jrccaim » Mon May 24, 2010 4:06 am

Really impressive, Peter (coming in late as usual). It reminds me of a Robert A. Heinlein novel. "The Cat who Walked through Walls," wherein there is a cat called Pixel, who walks through walls. Nobody bothered to tell Pixel that he couldn't. So he did.

The comments on mandrel size are interesting. The circumference of the mandrel is 2 pi R where R is the radius of the mandrel. As you push on the treadle, the string (or rope) goes at a speed S (meters/sec, ft/sec, whatever). So the speed of the rim of the mandrel is S. The angular velocity (rpm) is Om = S/R. Sorry about that but I can't think without greek letters; Om is Omega). So, the larger R the smaller the angular velocity. S is more or less constant because your muscles really can't be tuned like an electric motor! So it comes down to mandrel radius. Big radius, low spin rate; small radius, fast spin rate. There are so many variables it ain't worth calculating : is the wood dry? Is it gnarly? Is it soft? How fast is fast? What's an "optimum" mandrel size? How big is a piece of string?

That said, we resort to experiment. It would be worth having a few mandrel sizes and if you think the speed is too slow use a smaller mandrel; if you think it's spinning too fast, slow it down with a fatter mandrel.
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