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Discussion Starter · #1 ·
When you mount a bowl to a chuck do you create a tenon to clamp down on or do you create a recess to spread the jaws into to hold the bowl?

I there a reason for each?
Is knew particularly better than the other?
The rationale for each would be greatly appreciated.

Merry Christmas and New Years to all.
 

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A tenon is much stronger and safer than a recess. Using a chuck in expanding mode risks splitting the rim by prying the wood apart. The advantage though is the bottom can be finished, where with a tenon you have to reverse the bowl and cut the tenon off. It's a judgement call.
 

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Whether a tenon is stronger than a recess depends on the wood.

I recently was attempting to core a large walnut bowl blank about 14in dia x 9 in deep. Took 4 attempts. In the first 2 attempts the tenon broke off when we had a catch. The walnut at the tenon location was softer than other areas of the bowl.

My friend glued on a large base from dried heartwood walnut. Round 3 broke the tenon. We recut the tenon and it broke again. In hindsight we should have cut a recess and tried the jaws in expansion mode.

Round 4 my friend screwed a face plate to the large base. This was strong enough to hold up against the few catches we had.

I normally start with a tenon. If this breaks it can be fixed. As Maylar stated, in expansion mode you need to be careful you do not cause the blank to split.
 

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Discussion Starter · #4 ·
In some of the YouTube videos (Quality turners) I have seen they almost always use a glue block.

Is a glue block as safe as a tenon connected to the bowl?

My other question would be does the tenon need to be "dove tailed" or straight circular?

Had a bowl come off the lathe a few days ago. It scared me.... Lucky I was not standing in its line of fire (always try practicing that) , had all my safety gear on, face shield etc. Just trying to pinpoint what I did wrong... Thanks.
 

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I usually use a recess but occasionally a tenon. Most often if I use a tenon it is in dry wood.

I have to disagree with Maylar that a tenon is stronger. Work through your "pi X R Squared".
As 50mm jaws as an example, a recess with 1” surround provides three time the amount of wood to break away in the event of an oops as a tenon for the 50mm jaws.

Most of my items are functional so I tend to have the base about 1/3 of the diameter for bowls.
Tenons do leave more room for smaller bases if you wish a more artsy base. Of course you always use a tenon for spindle type mount.
Sometimes I use both; maybe my 70mm jaws in recess when green and 50mm in a tenon when dry.

Folks have excellent results with either if the wood is sound and the mounting proper.
Here is a link to Stuart Batty videos in which three which address tenons/recesses and chucking in great detail.
http://vimeo.com/woodturning/videos/page:1/sort:alphabetical/format:thumbnail
 

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Tenons don't have to be dovetailed although if you have Vicmarc chucks or chucks with dovetail jaws it helps. The most important thing is to have square shoulders at the bottom of the tenono for the jaws to sit on and the tenon should be short enough not to bottom out in the jaws. this shoulder not only aligns the bowl but helps prevent it from rocking while your turning. It's the rocking and vibrations and soft wood that makes the bowls come out of the chuck.
A recess is only as strong as the wood surrounding it. If you don't leave enough and get a catch it will break. A tenon can also break along the grain lines with a good catch. So the rule of thumb is to use the thickest tenon you can and if you do a recess keep as much wood as possible outside the tenon.
I generally reverse turn all of my bowls so I can leave the tenon or recess any size I want because I will be altering that area when I reverse turn to make the size foot or recess that I think is appropriate for thet bowl.
 

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Is a glue block as safe as a tenon connected to the bowl?
I would say it depends on the size of the glue block surface area.

My other question would be does the tenon need to be "dove tailed" or straight circular?
As John said, it depends on your chuck and jaws.
quote]

If you can state your chuck and jaws and a picture of the item it will probably help a lot.
 

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Discussion Starter · #8 ·
Not near my shop for pictures but I have the Nova G3 and I believe the Nova Super 2.... It may be called the Supernova2. Both by teknatool. I believe you guys may be familiar with that brand. I appreciate all the advice.
 

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Not near my shop for pictures but I have the Nova G3 and I believe the Nova Super 2.... It may be called the Supernova2. Both by teknatool. I believe you guys may be familiar with that brand. I appreciate all the advice.
I've got the Supernova2, it's jaws are interchangeable with the Nova G3.

The Nova standard bowl jaws are dovetailed, and Nova recommendation is to make the sidewall of recesses dovetailed to match the jaws.

They also make some jaws that are much deeper and have serrations on the inside faces -- these are designed to clamp around longer tenons without a dovetail.

(edit: removed erroneous content ... sorry for misleading information ...)
 

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Ack, you still don’t say what jaws you are using?
I have seven Nova’s (G3’s,SN’s, and SN2’s) All came with the 50mm bowl jaws. Nova/Teknatool may have changed but none of my 50mm bowl jaws have an interior tenon; they all have what Nova calls a lip. Of my eight different sets of Nova jaws none have an interior dovetail until I get to the 100mm jaws.
Below is a pic of my 50mm jaws with a machinist square. Note there is only a small lip at the top and most is straight on the interior. The lip is only 1mm wide so it can only bite into the wood 1mm deep. The exterior of the jaws do have a full dovetail.
If you have jaws like mine the drawing shows what can happen if you cut a dovetail on the spigot. You would have to crush the tenon at the bottom before the top edge even makes contact.
Here is a link to Nova for forming a spigot for most of their jaws. Scroll down to page 12 on Forming Spigot. Attention should be given to last line which is in all capital letters.
http://www.teknatool.com/products/Chucks/Nova/downloads/Nova%20Chuck%20Manual.pdf
 

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Discussion Starter · #11 ·
NCPaladin,

Oh! Haha. Thanks for pointing out whether it's 50mm or something different. I am assuming it's 50mm because of the picture you posted. But we all know what happens when you assume...

Any who... Thanks for posting that link. This has given me more insight into mounting in a chuck. Still have lots of practice ahead of me.

Anymore suggestions/tips from anyone is greatly appreciated. Thanks.
 

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I just edited my earlier post removing the comment about jaws having an interior dovetail.

However ... while that's true for the jaws that came with my SuperNova2 chuck, the 100mm jaws (JS-100) that I recently bought do have a dovetail on both inside and outside ...

The "standard" jaw profile ...



The JS-100 jaw profile ...

 

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Discussion Starter · #13 ·
I usually use a recess but occasionally a tenon. Most often if I use a tenon it is in dry wood.

I have to disagree with Maylar that a tenon is stronger. Work through your "pi X R Squared".
As 50mm jaws as an example, a recess with 1” surround provides three time the amount of wood to break away in the event of an oops as a tenon for the 50mm jaws.

Most of my items are functional so I tend to have the base about 1/3 of the diameter for bowls.
Tenons do leave more room for smaller bases if you wish a more artsy base. Of course you always use a tenon for spindle type mount.
Sometimes I use both; maybe my 70mm jaws in recess when green and 50mm in a tenon when dry.

Folks have excellent results with either if the wood is sound and the mounting proper.
Here is a link to Stuart Batty videos in which three which address tenons/recesses and chucking in great detail.
http://vimeo.com/woodturning/videos/page:1/sort:alphabetical/format:thumbnail
I watched almost every video of Stuart Batty on the link you put up.... This guy is so good it almost makes me angry haha!! Thanks for posting that.
 

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In some of the YouTube videos (Quality turners) I have seen they almost always use a glue block.

Is a glue block as safe as a tenon connected to the bowl?
My answer to this would be "no", for the simple reason because a person is creating more breaking points. Plus the person is allowing for more human error, is the fit good and tight, is the glue piece a decent piece of wood, is the glue up to the challenge. Now with that said, I use the glue method quite often simply because I don't like wasting my main piece of wood. I've had a few pieces not work out so great but 90% of the time no issue's.


My other question would be does the tenon need to be "dove tailed" or straight circular?
I believe this would fall under what type of chuck is being used, how big is the tenon and what type of wood is being turned. I'm sure others can answer this question much better than I :icon_smile:

Had a bowl come off the lathe a few days ago. It scared me.... Lucky I was not standing in its line of fire (always try practicing that) , had all my safety gear on, face shield etc. Just trying to pinpoint what I did wrong... Thanks.
You're an official turner now :laughing:..... stuff happens. Were you turning with a tenon or did you use a glue block? Either way I have had this happen (especially when I was green) with both. My scenario was not learning to "read" the piece I was turning and BANG got a nice catch, then it's ZING, BOOM, BOP and hopefully no one or thing gets in the way. What you did wrong, I think you should be happy for what you did right, standing out of the line of fire ;)

I was turning a beautiful piece of maple a few weeks back, stopped the lathe just to check my progress, everything looked nice, solid piece and smooth cuttings. Started the lathe back up taking real nice shavings and all of a sudden a piece about 6" long by 1.5" flew off and stuck straight into the ceiling above me. It had an old nasty spot deep inside the piece that could not be identified from simply looking at it, there was no way to tell it was going to be a loaded wooden bullet. My point being is that sometimes stuff happens, that's why standing out of the line of fire is so important.
 

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I use a glue block a lot. I use a good quality piece of wood. Turn a tenon on it with a shoulder just like I do on solid bowls. I glue it using a good quality glue and let it sit long enough to know the glue is dry. I haven't had a failure that I can remember. Usually if you have a failure of the glue block it's because you didn't get a good glue joint or the wood wasn't good quality.
 

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I have to disagree with Maylar that a tenon is stronger. Work through your "pi X R Squared".
As 50mm jaws as an example, a recess with 1” surround provides three time the amount of wood to break away in the event of an oops as a tenon for the 50mm jaws.
My comment stems from an engineering perspective, that wood is stronger in compression than in shear. You need to have enough thickness in the recessed lip to assure that the wood won't split.

And as for contact area, the outside circumference of the jaws will have full contact only at one specific diameter.

JMO, of course.
 

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“Using a chuck in expanding mode risks splitting the rim by prying the wood apart.”

I agree 100%. So I don’t do it (pry the wood apart); I just snug it up good. Never lost one in a recess mount.
I have also heard that it is almost impossible to crush a tenon. I also agree with this 100%. If the tenon is proper size you would have to physically crush the steel jaws of the chuck to crush the tenon and….nope :no: .…just checked… no red S on my chest.

“You need to have enough thickness in the recessed lip to assure that the wood won't split.”
Agree 100%, which is why Nova suggests an inch of wood surrounding a recess. Sometimes the size/design can not be achieved with the 1" surround and I go with a tenon instead.

And as for contact area, the outside circumference of the jaws will have full contact only at one specific diameter.”
I agree, and the inside only contacts at the corner of each jaw. Which gives more contact in circumference as the jaws are expanded into the wood I leave to the engineers as neither are ideal imho.

But that area was not what I intended by “area”. Sorry miscommunication on my part. Using a glue block as an example.
If you take a 2” diameter glue block and attach it in tenon mount there will be 3+ square inches of adhesion area. If you take a 4” diameter glue block (12” total area) and attach in recess there will be 9+ square inches of adhesion. (Thinking as a donut, 12” sq inch minus the 3” sq inch hole.) Three times as much whether it is a glue joint or the natural area of the wood. To me 3X area equals 3X strength. Most pics I see on damaged tenons are where the tenon itself sheared off and is still held in the chuck.

However, if you are going to have a 4” base you may as well have a 4” tenon and have the full 12” of area. Which brings to point; I do think there is some point of diminishing returns where a recess has less area than a tenon.

I think we agree in basic usage and sorry for my miscommunication.
 
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