Wedged through tenon question

[Aram]

My latest project will have through tenons. They will look somewhat like this, but will be better crafted, no blood on them, and they will be wedged. I stole this idea from a Krenov piece. The wedges will, of course, be vertical. Two of them per tenon.



I've made wedged through tenons before. Usually I cut saw kerfs in the tenon, and give the outsides of the mortise a slight bugle shape so that when the wedges are tapped in, the outer edges will have angled surfaces to register against. But that would look terrible here. The top tenon is not wedged, just the bottom two, and I don't want them wider than the top.

In theory cutting wedge shaped kerfs in the tenons, matching the wedge angle, should work. But they are tiny and I don't see a reasonable way to do that, even with the thin blades of my dozukis. I could cut straight kerfs and just kind of jam the wedges in there... I guess. 

I thought of one more way. Putting a slight taper on the left and right sides of the tenons, using a file or a hand plane. In theory, they might flex outward just the right amount when the wedges go in, and sit flush against the sides of the mortise. I'm not convinced. I might try it on a test piece though.

What's the right way?

[rayknight]

I don't think there is a uniform answer to you question.  I have always "bugle tapered" the outside of the mortise, BUT BARELY so, few draws with  med tooth file. I usually taper the tenon, slot cut the tenon down about 3/4 of the depth, again only mild taper. I usually use the bandsaw & and the taper is limited to dragging against the blade as I exit the cut.  I'm sure others have other approaches, but I agree a widely splayed tenon is not necessary, riskier & less attractive. others would argue ( possibly with less hard wood) that no taper is needed, but when I try that the wedge is so skinny you risk braking it as you tap it in.
Ray

[Aram]

I don't think there is a uniform answer to you question.  I have always "bugle tapered" the outside of the mortise, BUT BARELY so, few draws with  med tooth file. I usually taper the tenon, slot cut the tenon down about 3/4 of the depth, again only mild taper. I usually use the bandsaw & and the taper is limited to dragging against the blade as I exit the cut.  I'm sure others have other approaches, but I agree a widely splayed tenon is not necessary, riskier & less attractive. others would argue ( possibly with less hard wood) that no taper is needed, but when I try that the wedge is so skinny you risk braking it as you tap it in.
Ray

Thanks! Great points. I heartily agree about the "but barely" part.

Another thing, I went back to James Krenov, Worker in Wood (p.65 "Details"), and the lower tenons might be a little wider after all. I'll try it on a test piece. Maybe it would look ok.

[adamcherubini]

On Philadelphia chippendale chairs, the seat rails are through tenoned into the rear legs. This is an extremely highly stressed joint, maybe one of the most demanding of any joint I know including carpentry.

The mortises are cut square, typically from both sides in toward the center. The tenons are fit as always, straight. Saw kerfs were cut in the tenons top and bottom about 1/4-3/8” in. The joints were always glued, then (guessing) while still wet, wedges were driven in from the back. No tapers anywhere.

I think the saw kerfs need to be deep, possibly the full depth of the tenon.

I’m personally on the fence regarding glues. The pressure inside that mortise is uniquely high. Ditto, the wedge pressure. This theoretically could cause hide glue to extrude out of the joint, starving it of strength. On paper, this sounds like a good case for PVA.

These chairs have survived intact for over 250yrs. I don’t see why you couldn’t do the exact same thing.

[Aram]

On Philadelphia chippendale chairs, the seat rails are through tenoned into the rear legs. This is an extremely highly stressed joint, maybe one of the most demanding of any joint I know including carpentry.

The mortises are cut square, typically from both sides in toward the center. The tenons are fit as always, straight. Saw kerfs were cut in the tenons top and bottom about 1/4-3/8” in. The joints were always glued, then (guessing) while still wet, wedges were driven in from the back. No tapers anywhere.

I think the saw kerfs need to be deep, possibly the full depth of the tenon.

I’m personally on the fence regarding glues. The pressure inside that mortise is uniquely high. Ditto, the wedge pressure. This theoretically could cause hide glue to extrude out of the joint, starving it of strength. On paper, this sounds like a good case for PVA.

These chairs have survived intact for over 250yrs. I don’t see why you couldn’t do the exact same thing.

Thank you, Adam. Great information.

[jcousins2]

here is a link to rob cosman's video on doing wedged tenons - it's a very detailed description
https://www.youtube.com/watch?v=VE11nB4pnhM
jc

[Arlin Eastman]

This idea might make it harder but why not make a cross in the wedge to make it look different?   You would have to hand cut the wedges and shave the 4 ends to a taper but it might look great

[adamcherubini]

This idea might make it harder but why not make a cross in the wedge to make it look different?   You would have to hand cut the wedges and shave the 4 ends to a taper but it might look great

Sometimes people did that when wedging on a hammer handle. The problem with the cross shape is potentially blowing out the cheeks.You want the wedge action to work against end grain, not long grain. Or maybe I misunderstood

[Arlin Eastman]

Sometimes people did that when wedging on a hammer handle.  The problem with the cross shape is potentially blowing out the cheeks. You want the wedge action to work against end grain, not long grain.  Or maybe I misunderstood

No did not misunderstand buddy.  I meant the end grain of the tennon to look like a cross which would make it look different and not Phi look.

I did not know or think there would be a problem.  I am not much good at flat woodworking but a great turner.  



One of the reasons I come and read and see what others like you do.  

[Bill_Houghton]

No experience with this, but, if your concern is consistent dimensions at the exit side of the tenon, why not make the tenon that will be wedged a little narrower than the others, cut your mortise with tapered walls so that the visible (exit) dimension is consistent with the other mortises, and call it good?