One week down on the new website and it’s time for a little R&R.
I’m heading into the workshop to fix a chair (see link). I built it a year ago, and after one winter next to the heater, the joinery failed.
The joint in question is a bridle joint with an ebony loose tenon and ebony pegs. Unfortunately, the tenon didn’t hold and one of the joints broke along the miter. I think it had to do with racking on the front legs.
If you have any repair advice, please post it here.
http://www.taunton.com/fwn/gallery/galleryimage.aspx?id=23975
Matt Berger
Managing Editor
FineWoodworkingNetwork.com
Replies
Hi Matt,
I saw this chair on the front page of the site and then couldn't find your post in the myriad of tabs/locations on offer now.
Just an aside here, but I'm finding, on using the setup, that it's too long-winded and I don't have the time to read all the folders now, so I'll probably end up only reading one or two tabs - General and one other.
Anyway, to your chair. Stream-of-consciousness writing below, so things may be a little disjointed.
One joint can't fail without another failing also here. I'd check the opposite joint in the side for looseness (back leg/stretcher rail.) When you sit on the chair, the design of this chair has all weight trying to push the back leg away from the chair, with the single round mortise on the side stretcher being the only thing that stops it from moving away. In time, the glue here will fail by shear and then the 'bridle' joint will be loaded, causing failure.
I suspect that this has happened in this case.
[edit] I put 'bridle joint' in inverted commas as what you have here is a predominantly end-grain mitre joint with a pegged loose tongue providing the only structural strength, with the joint under shear in the design.
Ebony is a difficult wood to glue in any case due to it's density, so this could have contributed to the failure.
If the set based on this 'prototype' has to be built to this design, I'd be wary - wedged through tenons would be desirable [edit: on the joint between the stretcher rail and the leg,] but the leg thickness isn't sufficient to maintain structural strength with a through tenon.
Blind fox wedged tenons may work, but a bit fiddly and uncertain.
Let me know what you find please.
Cheers,
eddie
(a cabinetmaker who teaches schoolkids full time and builds studio furniture as a sideline business.)
Edited 11/18/2005 3:12 pm by eddiefromAustralia
Edited 11/18/2005 3:14 pm by eddiefromAustralia
<<< "...Blind fox wedged tenons may work, but a bit fiddly and uncertain..." >>>
Eddie: Please, what is a blind fox wedged tenon? Thanks-
Hi Yogi -
blind = not through the full thickness
fox wedged = similar to wedged tenon in US parlance. The only way to glue a fox-wedged tenon is to put the wedges loose into the tenon as you glue up and then, the action of clamping the joint home is what also drives the wedges into the joint.
I don't see too many pinned M&T joints here in Aust - more probably, the fox wedge was the method of choice, even though it's a bit of a pain in the proverbial to cut, glue and repair.
A google search brought up a few articles. Here's a reasonable description and illustration:
Cheers,
eddie
Eddie- Thank you muchly- I was aware of the joint, not the name- But I've always wondered (since I've never made one) how to be sure the insde of the mortise will actually accomodate the tenon once it's been fully seated and the wedge fully lodged- Sounds as if even a dry fit would be impossible to pull apart?
"Sounds as if even a dry fit would be impossible to pull apart?"
Hi Yogi,
You've got that right!
Unless you're willing to chop an identical through-mortise in a piece of scrap to test the joinery, you've only got one chance to assemble a fox-wedged M&T joint.
I have often thought about, but never followed through on, a variation of a fox-wedged M&T joint that starts with a flat-bottomed through mortise, and ends with a relatively thick piece being glued on to close the bottom of the mortise after the test fitting has been completed.
-Jazzdogg-
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
Sounds like we need some clarification from Eddie- Wonder if his experience can shed some light on other ways to approach the problem of fit?
HEY, EDDIE!
Hi Matt,
I notice that you also had chair next to the heater. If the glue was thermoplastic, it could have softened and contributed to failure.
Cheers (again)
eddie
Hi Matt,
If it were me, I'd seriously consider a more mechanically tenacious joint; the existing joinery appears (it's hard to tell from the photo) to be rather delicate, despite the pinned ebony spline. Perhaps a fox-wedged tenon, if you want the joinery to be invisible, or a simpler dovetail would suffice. Or you could emulate Sam Maloof and conceal a large screw behind a plug.
Your chair is similar to the ones built by Yeung Chan; have you considered asking for his opinion? I attended a three-day seminar conducted by him a few years ago and came away with respect and admiration for this world class craftsman.
Good luck,
-Jazzdogg-
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
Edited 11/19/2005 10:12 pm by jazzdogg
Edited 11/19/2005 10:14 pm by jazzdogg
Thanks everyone for the input. I took Jazzdog's advice for fixing this chair in the fashion of Sam Maloof: driving screws through the arms into the front posts to shore up the joints, and then plugging the holes.
However, I doubt this is going to solve the problem long term, so my next step is to take the seat off and replace the front stretcher with a larger stretcher that attaches to the legs with tenons. Right now, the front stretcher joins to the legs with round tenons, which allows the chair to rack side to side.
I think I'll go back to the drawing board on the joinery before making another.
- Matt
MBerger,
While your in that drawing room...maybe you might think about adding ####cross stretcher underneath....mine has sliding dovetails into the other two stretchers.
Old post but for what it is worth.. I KNOW Ebony a bit expensive but..
If it were me I'd 'think' like the metal worker in me.. Carefully cut out the 'spine' and drill out the 'pegs'..
Make it a bit longer and thicker and extend some of the Ebony 'under' the arms/legs..Hard to tell from the photo but sort of looks like it extends down a bit now??? Not sure... Oh and yes.. USE some of the Marine type glues.. They sort of like 'welding!'
Hey Matt,
When you get up from the chair, you probably push off right at this joint. The design is beautiful, but strength at this joint may haunt you a little bit. My first thought was that maybe the spline isn't large enough-i.e. not enough glue area for the stresses it's under. But that's a balancing act , you don't want to remove too much material from the leg and arm. For this prototype chair , I would fix it as is and see if it happens again.
For prototype #2 you may want to consider using a bridle joint, but eliminate the loose tenon. Have the tenon on the leg and the mortise (slot) on the arm. I've never really been a fan of loose tenons because it introduces a third piece of wood where two is usually enough. You could still peg the joint in a contrasting wood to achieve a similar design effect.
I think Hank Gilpin uses this type of joint on his "Blip" arm chairs. Check 'em out.
Best of luck,
-Paul
P.S. I'm not a long time poster here, but I don't mind the changes all that much. Keep up your hard work, I appreciate it.
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