Mortise or Tennon

[Dan Wiggin]

Hi all, I slid my headstock down on my Powermatic 2014 to rough turn this 18” behemoth of green Mahogany. I always use tenons but have never turned one this big on my lathe. Would I be better off to use a mortise instead? It seems it would be stronger. It’s very wet and heavy. Thanks in advance!

 

[Alan Weinberg]

Your tenon should be 30+% of the diameter of the piece. Yours is too small. Mortise isn’t necessarily stronger. Good luck.

 

[Dean Center]

Tenon vs. mortise seems to be one of those personal preferences topics, and you'll get recommendations for both here on the forum.

Personally, for an 18" rough blank, I would use a 4" tenon in my large chuck. Some folks can get away with a smaller tenon, if it's really well made. If so, I would suggest you keep the tail stock up as long as you can. Maybe that's not feasible on a 20" bed.

 

[Richard Coers]

My advice, stop trying to true the black from the outside diameter. Start cutting on the face and continue onto the O.D. Much less shock on your hands and the lathe. The answer to your question is do what you prefer. I use larger diameter jaws with my Oneway chuck when I do that size bowl. A stack of 18” bowls in soft maple.

 

[Bill Blasic]

I hardly ever use a mortise as I don't think they are as strong as a tenon. As most of my work is started on the Nova screw and I turn the piece and clamp to the 2"+ tenon size of the nova chuck the only time I use a bigger tenon is when I'm coring. The 30% tenon size is a good idea but for 25+ years I've got away with that 2"+ tenon.

 

[Dan Wiggin]

Thanks for all the advice guys! I think I’ll make a new tennon of the larger size. I think I can get close to that 30 % with my largest jaws

 

[Doug Freeman]

I use tenons 99% of the time. For 18” it would be ~6” dia. The initial tenon does NOT have to determine the shape of the lower part of the work. A smaller tenon can always be cut once the heavier load cutting is done. At times I may cut 3 tenons of reducing dia, depending on what shape I want to achieve, and/or if coring a bowl (which I would do with your blank).

 

[Dan Wiggin]

Thanks for the info Doug! Unfortunately I can’t core this one as I’m turning a18” blank on a 14” lathe using a lowered bed extension. (A first for me)