When are double tenons needed? (Old Dog trying to learn a lot of new tricks)

[george wilson]

I wouldn't bank on soft wood tenons not getting broken ahead of draw bored holes. If they are too offset,fir can just split on each edge of the hole,and move the slug of wood sideways.

I don't understand "2 tenons in line". I make my double tenons side by side. Maybe you refer to the tall,haunched tenon described above. In that case,yes,2 tenons would decrease the glue surface,but you also must consider the strength of the leg will be badly affected with just 1 tall tenon. At least haunching it provides an extra region of wood in the leg to help it not split.

[David Castor]

For what it is worth, this is what I was trying to describe originally (if this image comes through OK). I thought this might have some advantages over one longer tenon in terms of the expansion of the tenon.


Dave

Double_M_T.png

[george wilson]

Since any form of tenon that tall is still coming from the parent plank,I don't see that it would be less susceptible to expansion,possible glue line cracking,etc. Just pin it too. I had no problem with the tables I've made,but I only ever use pretty old wood that I've accumulated. My walnut was cut in 1941,and is my age! My mahogany is twice as old.

[Wilbur Pan]

I wouldn't bank on soft wood tenons not getting broken ahead of draw bored holes. If they are too offset,fir can just split on each edge of the hole,and move the slug of wood sideways.

When I did a dry run before making these joints, I found that if the holes were offset too much, the main issue was that the peg (I used 3/8" white oak) simply wouldn't go through and stop short. For these particular joints, the size and location of the hole compared to the thickness of the tenon really made splitting a non-issue. And when I did the drawboring, I could see the tenon piece move in towards the mortise, so I'm pretty confident that everything did its job.

I could see splitting the tenon being a problem if the holes were too big or too close to the end of the tenon. Luckily, it's easy to avoid that situation.