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Recess or tenon again. (Read 162 times)
 
George Stratton
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Recess or tenon again.
Oct 8th, 2019 at 10:04am
 
seems like not a lot of posts going on so i'll throw this in. My only chuck is the Nova with standard 2" jaws. Works great for what I can turn in this Delta lathe anyway, up to about 10" bowls. I'm fine with that. My questions are is a tenon a better hold or a dovetail recess? In a recess it seems that a diameter that allows the center of the jaw to locate would be best? On a tenon it seems that it would be better for the ends of the jaw to locate and dig in? Is my thinking right. I have only used a tenon on small 5 or 6 inch items and a recess on a few 10 inch bowls. Whats the safest way to go. Thanks in advance, Geo.
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robo_hippy
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Re: Recess or tenon again.
Reply #1 - Oct 8th, 2019 at 10:06am
 
There are many ways to do it..... Here is an old video:

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Ed Weber
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Re: Recess or tenon again.
Reply #2 - Oct 8th, 2019 at 10:42am
 
With "standard" 2" or 50mm jaws, a 10" bowl is too big for a tenon IMO
I would use a recess and leave an inch or more around the recess..
There is no difference in the holding capabilities between a recess or a tenon, providing they are cut properly to match the profile of the jaws.

That being said, the wood is the next place your connection could fail.
With a recess, the connection relies on a larger area (square inches of wood). A tenon is quite small in comparison
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Glenn Jacobs
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Re: Recess or tenon again.
Reply #3 - Oct 8th, 2019 at 10:53am
 
So much depends on the wood. Tenon for harder woods, Recess for softer woods. Not necessarily talking about the species. I have had soft (spalted) rock maple that needed recess and pine that could use a tenon.

Glenn J.
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George Stratton
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Old Delta 12" 46-701 in great condition. Had it about 20+ years and turned 1 part.
Re: Recess or tenon again.
Reply #4 - Oct 8th, 2019 at 2:45pm
 
The jaws on this 50mm chuck will actually hold a 2 3/8" dia. tenon even though they are made to only about a 1 3/4" actual diameter inside. Does it hold better on a larger tenon with the jaws digging in at the corners or the smaller tenon seating all around? Based on the same wood, it seems the larger tenon is best?? I'm kind of wondering where you guys have had failures??
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Ralph Fahringer
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Re: Recess or tenon again.
Reply #5 - Oct 8th, 2019 at 3:29pm
 
The theory I was taught was that the more closed the jaws are, the better the hold as more of the surface of the jaw is contacting the wood whereas the wider they are, as you state, only the corners of the jaws are in contact.
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Ed Weber
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Re: Recess or tenon again.
Reply #6 - Oct 8th, 2019 at 4:59pm
 
George Stratton wrote on Oct 8th, 2019 at 2:45pm:
Does it hold better on a larger tenon with the jaws digging in at the corners or the smaller tenon seating all around?


Too large a tenon and you have eight points of contact and no real benefit from the dovetailed profile.
Too small and it's a loose fit.
The Goldilocks zone is where the tenon matches the inside curvature of the jaws exactly. This way you are getting almost 360 degrees of contact and benefiting from the mechanical connection of the dovetail.
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Glenn Roberts
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Re: Recess or tenon again.
Reply #7 - Oct 8th, 2019 at 7:22pm
 
Darn! I make a recess for hard wood, tenon for soft. Doing it wrong again! My theory is that the hard wood has a less chance of splitting with the recess, the tenon should hold the softer wood - compression.
Hey Glenn, what am I missing?
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« Last Edit: Oct 8th, 2019 at 8:28pm by Glenn Roberts »  

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Ed Weber
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Re: Recess or tenon again.
Reply #8 - Oct 9th, 2019 at 8:56am
 
IMO
The wood species, hard or soft, is less important than cutting the blank properly for the jaws being used. Also the jaws being used should be the correct size for the blank being cut.
Jaws that are too small are more prone to loosen and/or snap off a tenon.

Those who cut green wood know that the recess or tenon distorts much more than dry wood when the chuck is tightened. Therefore, it's more important to cut dry blanks to the proper size and profile than it is when using green or very soft woods that have more give.

Please remember, it's not against the law to stop and check occasionally to be sure that the chuck is tight.  Undecided
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robo_hippy
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Re: Recess or tenon again.
Reply #9 - Oct 9th, 2019 at 10:18am
 
I don' think it can be over stated that you can over tighten a recess or a tenon, which can cause all sorts of problems. Mostly it is putting your grip under stress, and any added stress, like a catch can cause it to fail, especially if you are turning at high speeds. Harder woods are more brittle, and just like when you drop them, they are more prone to breaking under stress than softer woods which will tend to bounce rather than break. There are exceptions...... Every piece of wood is different. Rule for tenon: it should be 1/3 to 1/4 the diameter of the bowl.

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Ed Weber
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Re: Recess or tenon again.
Reply #10 - Oct 9th, 2019 at 11:06am
 
robo_hippy wrote on Oct 9th, 2019 at 10:18am:
I don' think it can be over stated that you can over tighten a recess or a tenon, which can cause all sorts of problems.


Thanks Reed, That's a whole other issue that I wasn't prepared to get into this morning.  Grin
Just to add a little more
There are static forces and many dynamic forces at play when you're turning.
Static force is basically limited to how much you tighten the chuck, it usually doesn't change.
Dynamic forces (forces that change) can be speed, friction, pressure, lateral force, rotational force, moisture content, internal structure of the wood and many, many more.
Turn safe
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Al Wasser
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Re: Recess or tenon again.
Reply #11 - Oct 9th, 2019 at 1:13pm
 
One also should consider design.  Generally speaking a tenon will create a small foot than a recess.  On say a 6-7" bowl a  smaller foot  will allow for a more curve  and I think look better.   Using the same 2" jaws a larger foot will look better on larger bowl or platter.  The ability of the turner to properly  create a recess comes into play.  I think it is harder to properly do a recess.    In both cases the jaws of your check should never dig or press directly into end grain.  If you just put the wood into the chock and don't pay attention to the grain you are doing  what  I call Russian roulette chucking
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Glenn Jacobs
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Re: Recess or tenon again.
Reply #12 - Oct 9th, 2019 at 2:33pm
 
Glenn Roberts wrote on Oct 8th, 2019 at 7:22pm:
Darn! I make a recess for hard wood, tenon for soft. Doing it wrong again! My theory is that the hard wood has a less chance of splitting with the recess, the tenon should hold the softer wood - compression.
Hey Glenn, what am I missing?



The area of a tenon circle (PI * R^2)  has the potential of being less than the area of the base of a bowl minus the diameter of the recess.

Glenn J.
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George Stratton
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Old Delta 12" 46-701 in great condition. Had it about 20+ years and turned 1 part.
Re: Recess or tenon again.
Reply #13 - Oct 9th, 2019 at 5:37pm
 
Thanks for all that guys. I think i agree with Eds "Goldilocks" zone and i'll shoot for that from now on. Most of my tenon work has had the corners of the jaws digging in. Thanks.
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