Recommened tenon diameter to bowl/vessel diameter ???

[Glen Blanchard]

Is there such a thing? If so, what is it?

I have a Delta 46-460 midi lathe, which has a 12.5" swing. My largest scroll chuck jaws move (in compression mode) from 3.071" up to 3.898". As jaws are more effective when almost closed, I would make a tenon slightly larger than 3" in diameter to use with these jaws. Would this be sufficient to hold a bowl/hollow vessel that is in the 11" to 12" range?

[Fred Belknap]

Yes, just make sure the wood is sound and the right shape, different chucks have a little different design. I regularly turn bowls that size using 2 to 2.5" tenons. I use the tail stock till I get the outside and part of the inside pretty well done.

[Dennis Ford]

I agree with Fred, you should be OK. I use similiar size tenons for larger pieces sometimes.

[John Keeton]

Glen, that determination depends more on the extension (depth) of the piece than the diameter. For instance, looking at the Nova chuck jaw manual, the specs for the 100mm jaw include a bowl up to 12" x 4" deep, or 6" x 5" deep. As you can see, adding depth significantly affects the integrity of the clamping efficiency of the jaws.

I have a larger set of jaws, but nearly everything I turn is done with 50mm (2") jaws. That includes a few (very few!) bowls that sometimes exceed 12", and all of my urns, etc. However, I always use a steady for extended work, and like Fred, I use tailstock pressure as long as feasible.

[Justin Stephen]

Just make sure you are accounting for tenon warp if you are starting with green wood. If you use a green tenon that is too close to the minimum diameter that your chuck can handle, once you re-round it when dry, it may be too small for your chuck. On the other hand, you want a very firm hold on a green tenon since the blank will weigh so much at that point so using a tenon that is close to the maximum diameter of your chuck is bad too. It's all about finding the happy medium.

[Reed Gray]

I have always heard, 1/4 to 1/3 the diameter of the bowl. So for a 12 inch bowl, you want a tenon in the 3 to 4 inch diameter range. This might be a bit of overkill, but I core, and you do want a little extra. You can turn a 12 inch bowl with a 2 inch tenon, but that is kind of minimal, and if you have a catch, that might just be the straw that broke the camel's back. Like John said, if you are going deeper, then you also want a little extra. I would use a much bigger tenon on a hollow form than on a bowl. Never use a recess when turning end grain.

robo hippy

[Leo Van Der Loo]

On a blank that still has to be rough turned I will use a faceplate to do this, when the outside is shaped I will cut a recess.

I like to go close to 1/4 of the turnings size, depending what I'm turning, like a 20" platter will not get a recess that's 1/4 of it's size, and yes I seldom use a tenon, if at all possible I use a recess.

And I have heard all the opinions of the splitting and breakout etc., I normally go 1/4" to 3/8" deep and make sure the recess is square and clean where the jaws will seat.

I tighten the chuck one-handed with the key, rotating and retightening a few times, a solid piece of wood without splits already present will not split from that and will hold the blank just fine, mind you I seldom have a catch anymore, but even so that was not always the case.

I should add that I use Oneway Talon chucks on my 46-460, and it will open to 4 5/8" in a recess, on my large lathe I use a Oneway Stronghold, it opens up farther.

I really like the Oneway chucks with the profiled jaws, they hold well over the full range of the chucks.

www.oneway.ca:chucks:talon_capacity.htm.


This is a recess in a 20" bowl, turned without tailstock help.
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This shallow bowl shows where the recess was, smaller than the foot is now, and of course that foot can be totally removed if you don't like a foot.
254256

Yes I do have experience turning bowls, this is a load of rough turned ones a hauled to our new place, it shows only a few bowl bottoms, but they have recesses.
254257

[Prashun Patel]

I have the 46-460 too with a Nova G3 chuck which only goes up to about 2 1/4" wide. I make my tenons that big even when turning a 12" dia, 6" deep bowl. I always engage the tail stock when possible, though.

I am amazed at how better things hold when the tenon is properly shaped and the blank is properly prepped and centered.

[Chip Sutherland]

I guess I follow Reed/Robo Hippy's approach of 1/3 to 1/4. My max jaw chuck is 100mm. For green wood I always go for a larger and thicker tenon to accommodate the need to re-turn the tenon to combat warpage. For bowls/platters, the size of the tenon also has to do with the size of the foot I'm planning. I don't use recesses any more. They are so easy in the beginning but I eventually broke out a few sides (launching projectiles) and had some design challenges I am happy to NOT repeat.

My HFs get longer tenons. Seems I have a bad habit of needing just a little extra for the bottom of the HF and that extra long tenon has saved my butt/piece numerous times. I think the longer tenons on HFs also tolerate the hollowing out stresses better but I still use a steady rest too. Looking at some my WIP HF pieces, I would say that my HFs are 1/3 - 1/2 the diameter of the HF.

Ultimately, the final decision comes down to 1) which chuck is available 2) what jaws are available 3) Do I feel like swapping jaws (i.e. how lazy am I).

[Thom Sturgill]

Chip, rather than a longer tenon, think about using a faceplate. I just ordered a small aluminium faceplate for that purpose. I had never used one, mainly because of the size of the stock faceplates. I recently sat through a session with Lyle Jameson who says he never uses a chuck or steady. His demo convinced me to at least give faceplates a try for hollow forms. They can handle more overhang than chucks.

[robert baccus]

I think the focus here has been mostly on the machinery. All good advice. I would add that the very first observation and decesion factor would be the wood. Are we talking dry Osage or green aspen here. Everything depends on this I think. I think you would have a death wish to turn green aspen on any tenon known to man--a piece of any size! I like hollow dovetails but not on green wood. Would a dry hardwood GB qualify here??


I've launched more than NASA has.

[Brian Kent]

On the bottom end of the experience scale, I almost always start with a faceplate, then turn a recess instead of a tenon. I frequently have problems with tenons (because I do have a lot of small catches) and never have problems with recesses. I have a Delta 46-460 with a Nova chuck.

[Leo Van Der Loo]

I think the focus here has been mostly on the machinery. All good advice. I would add that the very first observation and decesion factor would be the wood. Are we talking dry Osage or green aspen here. Everything depends on this I think. I think you would have a death wish to turn green aspen on any tenon known to man--a piece of any size! I like hollow dovetails but not on green wood. Would a dry hardwood GB qualify here??


I've launched more than NASA has.

A green spalted and stained piece of Aspen here, did a couple more, they are held with a recess on my Talon Chuck.

254311



The wood species has not been my deciding factor, more the soundness of the wood, that is no splits or checks to start of with, then choosing the cuts and tool presentation that wil put the least strain on the hold of the piece, hogging is not in my turning vocabulary.

[Brian Kent]

Leo, that is astounding. How thin does aspen need to be in order to be translucent?

[art pfenn]

I agree with John the depth is a huge factor. I launched a piece that flattened my face shield and almost broke my face. The tenon was bad but more important the piece was way too long at least for a beginner. I was using the Delta 46-460 and a Nova chuck.