# Newbie questions on tenon length....



## Jim Beam (Oct 10, 2012)

Hi All

Going through the learning curve here...

What is your preference - a recessed tenon that you grab by expanding your chuck, or a protruding tenon that you grab by tightening your chuck? I've done both, and kind of like the protruding tenon because I can make a jamb chuck after hollowing the bowl and then take the tenon off, leaving a nice clean bottom to the bowl. It_ is_ an extra step though.

I have a Nova G3 chuck. The jaws are 3/8" deep. What is the minimum tenon length or depth that is safe? I know this is a subjective question with many variables, like height and diameter of bowl. But the deeper or taller I make the tenon means less wood available for making the bowl deeper.Any input or feedback is appreciated.


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## sawdustfactory (Jan 30, 2011)

I prefer tenons too. As for length you want enough material so the chuck can get a good grip. You don't want it bottoming out in the chuck. You want to make sure the shoulder of the tenon is flat so the jaws can register against them.


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## 9thousandfeet (Dec 28, 2014)

Depends on the situation.

I always use a tenon, never a recess, when rough turning. Always.

I use a tenon much more often than a recess for finish turning, often for the reason you state about being able to remove it later to give a nice clean bottom to a bowl with no real "foot". 

Sometimes I use a foot specifically designed, and sized, to be gripped by a chuck without damaging it (I use smooth dovetail jaws—this won't work with the "profiled jaws") thereby avoiding the extra fixing to finish the bottom after turning the inside. Raffan discusses this approach at length. It does somewhat limit design options, but it's much faster for production situations.

I do use a recess for some platter work, and for "art" pieces intended to be hung on a wall and such. I also put a recess in the center of a large blank if I'm going to core it, so I have the ability to reverse-chuck the extracted core. That recess will eventually disappear in the hollowing of the smallest core.

In general I find tenons faster and less fussy to turn than recesses, so I tend to use them by default, turning to a recess only in more specialized situations.


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## Jerry Maske (Dec 29, 2013)

And I stand on the other side of the street. I like the recessed opening and the expansion process. As long as you dovetail the sides and make sure you leave enough wood outside to prevent the jaws from cracking, you've got an easy grip that cleans up a lot faster than a spigot tenon, in my humble opinion. No problem cleaning up with a jamb chuck and a Nova plug. Then a little hand sanding and I'm done. Also, this method provides a nice base where the bowl comes all the way to the bottom. And it's easy to adapt to another style on the jamb chuck if you want to. Okay, it's personal preference. I don't know many other turners that do it my way, and that alone is good enough reason for me to keep at it.

Jerry


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## NCPaladin (Aug 7, 2010)

I'm on the side of the street with the Rev.
I use a recess if size permits mainly because there is three times the amount of wood to break away with a recess compared to a tenon in the event of an unscheduled launch (at least with the 50mm jaws).

I do use a tenon sometimes but mainly when an item is a smaller diameter. I usually make my tenons about 3/8" but it depends on the wood. 

I have never used a jamb chuck except for boxes. It just seems like a lot of time spent in fitting for what may be a one-off turning.

A friction drive (chuck) is quick and easy, whether recess or tenon, and allows you to reshape the foot. The small nub is removed and sanded off of the lathe. In most cases I think I can return the base and remove the nub before I could even have a jamb chuck made.
Once reworked the recess is maybe 1/32 to 1/16" deep with no indication of how it was held.

I'm not sure what a "Nova plug" is.


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## 9thousandfeet (Dec 28, 2014)

One situation where I personally find there is an advantage to using a tenon, and especially if used in conjunction with what Ellsworth calls a "base cut" but what I've always thought of as a "fudge factor"—basically another tenon somewhat bigger in diameter than the one the chuck will grip—is when I'm designing a bowl as I go along and intend to design the foot last. 

I find being able to see exactly where the bottom of the tenon/basecut combination is at all times to be reassuring when hollowing the interior. 

With a recess I find myself fretting that I'll turn the inside profile of the bowl too thin at the bottom, which in addition to affecting the balance can also cause the bowl to make a "tinny" or otherwise disagreeable sound when one sets it down on a table, instead of a pleasing "marimba" kind of sound. 
When that happens it's woodstove material immediately, because I just hate either of those faults and there's no medicine for them.

With production runs of bowl profiles which are part of my standard output, none of this is an issue because I know exactly what works and what doesn't from having done hundreds of them, but with new designs I really like to be able to see, visually, exactly how much timber I have remaining as I hollow the interior. With a recess I can't visually reassure myself constantly, and that distracts me. 

This is a personal mental thing as far as I can tell, 'cos even though I can't "see" the bottom with a recess like I can with a tenon, since I'm the one who turned the recess I still have a pretty damn good idea where it is, so it's not like it's a big mystery or anything. It's strange, but there it is.


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## Maylar (Sep 3, 2013)

I like a recess because it wastes less wood and I can completely turn and finish the outside and bottom of a bowl. I have an arbor that mounts in the tailstock, allowing me to mount the recess to my chuck and center it before removing the faceplate from the lathe.


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## Jim Beam (Oct 10, 2012)

Thanks to all for the replies! I didn't quite get what I was looking for though.

What is the shortest tenon that you are comfortable with? I know this is subjective and varies between people and the size of the work piece.

I have a bowl on the machine now with a tenon that is 7/32" tall. It seems to be holding fine? Can I go shorter, or would that be pushing my luck?


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## sawdustfactory (Jan 30, 2011)

I think you answered your own question, really depends upon the piece. Smaller piece, short tenon with good shoulder, sharp tools and light cuts no problem at all.


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## hwebb99 (Nov 27, 2012)

On a small piece an 1/8 tenon would be fine. On a larger piece I would go with the longest tenon your jaws can hold without bottoming out. I wouldn't turn a bowl bigger than about 8 inches with 50 mm jaws. Most turners say that a tenon that perfectly fits the jaw is the strongest. With properly sized jaws they might be right, but after breaking several 50 mm tenons I decided a larger one is stronger.


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## 9thousandfeet (Dec 28, 2014)

Jim Beam said:


> I have a bowl on the machine now with a tenon that is 7/32" tall. It seems to be holding fine? Can I go shorter, or would that be pushing my luck?


 The smartass answer is that if the chuck loses its hold and the piece starts racing around on the floor terrifying the shop cat, then the tenon could well have been too short.

But just to muddy the waters a little more, the diameter of the tenon is a big factor too.
A tenon much smaller than 1/3 of the diameter of the workpiece (this is not a rule, just an observation arising out of my own work) can be problematic no matter how tall it is. 

It's _possible_ to hold a 10" salad bowl on a 2" tenon maybe 3/16" tall or even 1/8" tall if the wood is strong and sound, but vibration and other instability problems can cause chatter and difficulty getting a clean cut, and those problems can persist even if the tenon is taller. 

So possible is not the same as optimal. A 10" bowl held on a 4" tenon which is only 1/8" tall can actually give more stable performance than the same bowl on a 2" tenon 3/8" tall—assuming both are fitted to chuck jaws of appropriate size.

In general, I'll use a tenon and matching chuck jaws which are as large in diameter as possible consistent with the design of the piece, and if I do that, any tenon more than 1/8" tall will almost always give me a hold that won't fail.


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## NCPaladin (Aug 7, 2010)

I tend to go longer with a tenon than most, typically at least 3/8" but it all depends on the wood and the size. With a shallow bowl I may go 1/4". If the wood is strong and dry I may even go down to 1/8" on smaller items.

Hwebb mentioned going to a larger diameter after "breaking" several. Two things can happen. Either you can break a tenon, usually sheared off along the grain, or leveraged out with the tenon in tact. Most that I have seen have broken off and I don't think the length of the tenon has much effect. 
Several months back my daughter was tuning about a 10-11" bowl and had a catch; the tenon held but it was leveraged out on one side at least 1/4". If it had been <1/4" it would have launched.

Hwebb is correct that a larger tenon decreases the probability of the tenon being sheared off. The 70mm is one of the least expensive sets of jaws and my go to for most items ($35 on amazon). Going from 50mm to 70mm you are _doubling the area_ of wood that has to shear off for a launch. 
Many times I may rough turn with the 70's and drop down to the 50's for finish turning.

To answer you question of "I have a bowl on the machine now with a tenon that is 7/32" tall. It seems to be holding fine? Can I go shorter, or would that be pushing my luck?"
If I need to preserve wood I would go with a recess rather than a tenon but that's just me.

Nova does define spigot (tenon) mount as endgrain, nence the smaller diameter and length of the item. On page 20 & 21 they list _maximum_ recess of 1/4" but _minimum_ length of spigot at 5/8".
http://www.teknatool.com/products/Chuck_Accessories/General/downloads/Accessory Jaw Manual_Nov07.pdf


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## hwebb99 (Nov 27, 2012)

I was experiencing both problems with it levering out and shearing off with the grain. I sent my SN2 chuck back to woodcraft, and I bought a Oneway stronghold chuck. That chuck has completely fixed both problems.


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## Jim Beam (Oct 10, 2012)

Thanks to all for the discussion. As I said, I'm new to this and am only now turning my 4th bowl. Have not had anything fly off the lathe yet.

One thing I have learned - turning is fun, sanding is not.


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