Tenon question

About 4" maximum width Luke

Andrewf in Australia

>Beyond that, use a castellated tenon if it's critical that shoulders are hidden.

I'm just finishing a bench where it isn't critical, so I left 3/8" gap at the end of the mortice and glued the other end only.

Cheers,

Andrew

I don't get it

Adam Cherubini, NJ

>Is there a rule of thumb for what a max length (depth) of a glued in tenon can be without causing expansion problems because of the cross grain relationship to the mortise?

I don't get it. The mortise defines the tenon. Not vice versa. The depth of the mortise is defined by:

1) The size of the peg. The trunnel hole should be at least 1-1/2 diameters from the shoulder, and there should be another 1-1/2 d on the other side (toward teh bitter end of the tenon. That means the mortise must be at least 4 diameters plus something deep. For a 1/4" peg, I'd make at least an 1-1/4" long tenon, 1-3/8" deep mortise. Okay?

2) The length of the mortise. Its difficult for a normal joiner (with a normal joiner's mortise chisel) to cut deep, short mortises.

FWIW, short ,deep mortises are the work of the sash joiner and his specialized sash mortise chisel (which is like a super heavy duty firmer). Modern companies seem to be confusing these tools, the point behind their designs, and their proper use.

Is this why tenons are tusked or pegged when they are pretty big?

I'm not sure where tusked tenons came about or what the original application was. But I see pegged tenons on all sizes of M&T joints from chairs and stools, to tables, to barns. Its uncommon to see tenons simply glued in. This is often a nonstructural joint. (maybe a drawer blade/guide).

Can they be glued for an inch or two near the shoulder to add strength, but left unglued on the rest of the cheek?

I'm not sure what problem you are solving by gluing a little. So the bitter end of the tenon is allowed to move, but not the shoulder end?

Gluing M&T is tricky anyway. If you do glue, you should use something with gap filling properties. I think that means hide glue or epoxy. Polyurethane (Gorilla glue) physically fills gaps, but doesn't structurally fill. If you are really concerned, make your style and rails 1/4 sawn.

If I misunderstood the problem, please write back and tell me to shut it! Say, "Adam, you shut your pie hole, you great fat article!" If you could say that with Irish accent, that would be much appreciated.

Adam

(spent the day yucking it up with my friends from the U.K.)

the whassa, whossa...huh?

Luke Herzberg

>Now I'm confused! : )

Okay, these tenons are cut in a 4 x 4 stick o' wood. (none of the 4/4, 16/4 nonsense...I work with dimension lumber : )

The tenon is cut in the end of the piece and is about 6" long. Since the tenon is quite a bit longer than wide, I was more concerned about the movement of the mortise piece (mortise getting deeper or shallower), then the tenon width changing. From your explanation, maybe what I've done is just make tenons that are way too long to do any extra good. If I used a 1" peg, that would mean a total of 4" tenon length with your formula. Hell, the peg is probably way oversized to boot.

The mortises for these pieces will come from laminating some 2x12's together, face to face, so the mortise would be cut from an interior piece before glue up (like dog holes on a bench), so I wasn't concerned about mortising out their extra length.

The tenons are the bottom of my bench legs, and the glued up 2x12's will be the cross piece...the feet I guess you could say (probably a lot more technical terms that I don't know for all these things).

Well anyhow, I think what I will do is just leave the tenon long, don't glue, and peg it up closer to the shoulder in the spot where a proper length tenon should go (they're such nice tenons I hate to prune them). Besides, I realized later this afternoon that gluing would be practically impossible because of the time required to slip in a whole slew of tongue and groove paneling captured by these pieces...Aaaaaagghhh, why do I feel like I'm reinventing the wheel!!

But seriously, that did help out, Adam.

oh yeah...and ya shoot yer poyhole ya grit fot orticle!!

Thanks,

Luke - forgetting two things for every one learned.

Re: Tenon question

Frank Joseph Mantua NJ

>cut your depth deeper with a deep tennon at 6' IN A SOFT WOOD YOU WILL NEED AT LEAST 1/4 INCH.

I would glue the heel and pin the tennon at 50% with a hard wood square peg. I am assuming its a inside item. if its for out door use I think it shoud be peged only. and give all sides some room to move.

Re: the whassa, whossa...huh?

Adam Cherubini, NJ

>Luke,

I got a real charge out of your accent! Thanks for the chuckle!

I think I�m with you. Sounds like you are using construction lumber to build a bench. 4x4�s for legs with a glued up 4x12 sled foot

thinking out loud (that�s a big foot, or are you going to rip it in half?...hmmm...probably. That would explain the 6� long tenon.)

Was your concern that the differential movement would break the bond? Or that the tenon would protrude out from under the sled foot? I think that's a valid concern.

Since the tenon is quite a bit longer than wide, I was more concerned about the movement of the mortise piece (mortise getting deeper or shallower), then the tenon width changing.

Well, both are going to happen. If you had a dry mortise (not through) the tenon�s end grain would be protected and maybe you�d see less tenon width change. On my bench the sled feet ends aren�t only exposed, they are rounded which exposes MORE end grain. So I agree with you. The mortise WILL change depth.

From your explanation, maybe what I've done is just make tenons that are way too long to do any extra good.

Well not so fast. You need to decide where the rotation will be taken out. Usually, rotation is handled at the shoulder through the intimate contact there. But with construction lumber you could see the sled foot shrinking enough to introduce a gap. In that case, the long tenon in a tight mortise could react the rotation (caused by the force of planing). I�d leave your tenons long and make your mortises as tight as you can without forcing stuff together.

If I used a 1" peg, that would mean a total of 4" tenon length with your formula. Hell, the peg is probably way oversized to boot.

Right! That peg should be no larger than 5/8� dia. 3/8� would probably be fine. You need that guy to bend a little since you must drawbore that joint. Make sure your pegs are dry riven stock and taper one end to help you align everything. If your peg cracks during installation and breaks off in there, you�re screwed. You only get the one chance at it, so turn off the radio and listen to it sing as it goes in. If it stops ringing, drift it out carefully with a smaller peg from the other side.

Well anyhow, I think what I will do is just leave the tenon long, don't glue, and peg it up closer to the shoulder in the spot where a proper length tenon should go (they're such nice tenons I hate to prune them).

Give yourself a little extra room since you�ve got it. We put our trunnels near the tenon shoulders because we have to. Shoot closer for the middle of the joint.

Luke - forgetting two things for every one learned.

Don�t forget what I�m tellin ya! Not enough guys know this stuff now. Must we all make the same mistakes? Thanks to Ellis we can share our experiences with others and hopefully save them the time, money, and frustration blah blah blah ...

Oh shut it Adam, YOU RAGING LOONEY!

Re: the whassa, whossa...huh?

Luke Herzberg

>Alright, thanks again for the help, Adam. Soooo, it's called a sled foot eh? (another thing learned...anniversary and SSN forgotten). You didn't think I was forgetting valuable woodworking knowledge!!??

The 2x12's for the feet won't be ripped in half, just big heavy suckers. The tenons on the bottom of the legs probably would have been the full 12" if I hadn't already needed to shorten the legs because of...ummm, "interperative sawing" for the tenons on the top end. (Yes, there are tenons into the bench top too. Don't bother correcting me on that one, it's too late to change it ; ).

As far as my concern about the wood movement, it was fear of breaking the glue bond that prompted that. I originally was thinking glue only, no pegs. Now I'm thinking pegs only, no glue...problems solved.

Anyhow, recent progress has been good on this eternal bench project. Hopefully have some pictures to post soon.

Thanks,

Luke