Tenon Size: Is jaw contact area really all that matters?

[Leo Van Der Loo]

Yes, there are two different factors being discussed here (and I've really appreciated the input thus far on both). One is how easily the tenon will break. The other is the gripping power. What if I am confident that my tenon won't break? Speaking strictly on gripping power, does the diameter matter above the minimum external capacity?

Sometimes, for example, I'll use a hefty tenon (.5"-.75" deep) with tower jaws so that I can be more aggressive while hollowing than I would be with a shallower tenon. I'm not concerned about the tenon breaking here.

The holding of dovetail jaws, whatever size you use, is when the jaws have full contact, the problem you run into with roughing a blank that isn’t dry, is that your tenon shrinks, the tenon than is too small for the full contact.

Going with a recess, you have a larger circle to start off with, (outside dimension of the jaws) and when the rough out has dried and shrunk, you can open it up to the original size, best you can do.

I use the Oneway patented proofed jaws, they will have a better holding power if you go to tenon sizes that are larger than the full contact dovetail that seldom have the ideal size for wood will shrink and sizes change.

I have turned many large bowls and use the recess, I don’t have turnings come out of my chuck, and I am not confined to having to use one particulate size recess, but can make them suited to the size bowl I am turning.

[Thom Sturgill]

Some good point have been made here. I agree fully with Michael Mills that if you want a larger diameter tenon - use larger jaws. If turning green to be re-turned - start with larger jaws and expect to re-shape the tenon for smaller jaws when the bowl is ready to be re-turned. I have seen demos of hold failures with over and under sized tenons where the demonstrator pulled the bowl from the chuck and showing the bite marks left by the chuck.

[John Beaver]

I try to make the tenon just slightly larger then the final foot of the vessel. If you have a large bowl that requires a 5-6" base, and you use a 2-3" tenon, then you will have to turn that tenon away later and you lose that wood. Sometimes that is fine, other times you might want that extra wood. I then use the appropriate jaws that fit that tenon the best. That way I am starting off with everything in my favor limiting the potential for problems. Every step you can take that minimizes risk will help you along the way.

I do a fair amount of teaching and I will say the number one cause of bowls flying off the lathe is incorrectly made tenons. Specifically the shoulder not being flat, square and sharp. You can err quite a lot on jaw sizes etc, but if the tenon is not made correctly you are prone to problems.

[Reed Gray]

I mostly use a recess, but for the best and most secure grip, the tenon needs to be just slightly larger than the chuck jaws when they are closed on it. The tenon needs to be sized for the project you are turning. A rule of thumb is in the 1/3 to 1/4 the diameter range.So for a 12 inch diameter bowl, a 3 inch tenon is very secure, a 4 inch is almost unbreakable. A 2 inch tenon would be pretty minimal as in you might get away with it if you don't have any catches, and/or are not coring...

robo hippy

[John Keeton]

Reed, I think there may be another factor and that is the style of turning. You are a brute of a man and I have watched you turn! The forces you exert are way beyond what I could or do - barring any catches.

[Reed Gray]

Fezzig 'I'm on the Brute Squad.'
Miracle Max, 'You are the Brute Squad!'
John, it is deceptive.... I was chatting with Dave Schweitzer of D Way tools after the Oregon Woodturning Symposium last spring and he commented that several people told him 'what that hippy does with scrapers is scarey!' I am thinking, hey, it is just a scraper. After pondering that for a while, I started thinking that it maybe is like me thinking about the skew, which is a 4 letter word do me.... But, I am getting better at it...
robo hippy

[John K Jordan]

Fezzig 'I'm on the Brute Squad.'
Miracle Max, 'You are the Brute Squad!'
John, it is deceptive.... I was chatting with Dave Schweitzer of D Way tools after the Oregon Woodturning Symposium last spring and he commented that several people told him 'what that hippy does with scrapers is scarey!' I am thinking, hey, it is just a scraper. After pondering that for a while, I started thinking that it maybe is like me thinking about the skew, which is a 4 letter word do me.... But, I am getting better at it...
robo hippy

Hey, let's meet 1/2 way across the country. You bring your "Fun with Scrapers" instruction and I'll trade with "The Joy of Skews".

BTW, I'm seeing odd characters in your messages where there is a quotation mark - are you seeing that? Someone else was having similar but different issues. I don't see the problem in the quoted text in my message. I'm still wondering about the editor - which editor are you using in SMC? (Settings/General, at the bottom)

JKJ

[Reed Gray]

<p>
Hmm, I didn&#39;t see those on this end. My computer died last Saturday and I have a new one... Last one was 10 years old... I have some &#39;adjusting&#39; to do... I didn&#39;t see you in KC last year. I will be in Portland next year since it is just down river, or up the road from me... I will have a double space and a lathe to play on. I want to get Mike Mahoney in the booth if he is there to show him how to use scrapers for bowl turning, and for shear scraping....</p>
<p>
After I posted, there it was again. The apostrophy isn&#39;t translating through my new computer and this web site.... Clueless!</p>
<p>
robo hippy</p>

[John K Jordan]

I haven't been to KC for 40 years. Maybe it was the other John Jordan, the famous one.

Your post was full of confusing character codes! The post you just made is also full of "p" codes for some reason. Another guy was having each quotation mark display a code instead of the character. Who knows why.

I still wonder which editor you are using within SMC (under Settings/General). If you haven't tried it, maybe try switching temporarily to the Standard editor and see if it displays the correct characters.

JKJ

<p>
Hmm, I didn't see those on this end. My computer died last Saturday and I have a new one... Last one was 10 years old... I have some 'adjusting' to do... I didn't see you in KC last year. I will be in Portland next year since it is just down river, or up the road from me... I will have a double space and a lathe to play on. I want to get Mike Mahoney in the booth if he is there to show him how to use scrapers for bowl turning, and for shear scraping....</p>
<p>
After I posted, there it was again. The apostrophy isn't translating through my new computer and this web site.... Clueless!</p>
<p>
robo hippy</p>

[Richard Dooling]

Don't mean to hi-jack but as a comment:
One of the odd character sets displayed in Reed's posts is the HTML code for apostrophe. I can't even type it in here without it reverting to an apostrophe.

https://www.w3.org/MarkUp/html-spec/html-spec_13.html

Reed, are you by chance typing in MS word or another program an then pasting into SMC? In advanced reply option the Paste as plain text or Paste from Word options might help. I suspect that when Reply with quote is used the text has all formatting removed. Tech support might know.