Mortise/tennon question

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While at the Woodworking show last week I saw a demonstration for the Leigh mortise/tennon jig. The guy doing the demo pointed out that furniture made with mortise and tennon joints lasted 100s of years.
I can understand why an extremely well fitting joint was required in the "old days" since the glue wasn't great, but with the glue available today do the joints need to be as perfectly fitting? Craftsmanship aside, does a somewhat rough joint significantly less strong than a perfectly fitted joint over time?
Just curious if the $800 they wanted for the jig actually produced a dramatically stronger joint.
Jim
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In rec.woodworking

No doubt. Of course, that was the most common method of joinery hundreds of years ago too.

Nope
It would be better yes because if the glue is softer than the wood, it will compress and the joint will loosen. If the glue is harder than the wood, it may weaken the wood through racking over time. It may also be more brittle and just crack.

Than what? I use a $99 mortiser and a homemade tall fence with a C-clamp and get perfectly fit joints. In any event, while "dramatically stronger" is subjective, I'd have to say no it does not. No way in hell it does really if you take "dramatically stronger" to mean an order of magnitude.
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Bruce responds:

Probably not dramatically stronger, but my understanding is that the jig makes the use of angled and muliple tenons a great deal easier and quicker: I've watched it being used, and the speed is truly impressive, once you learn to set the jig up (not a small chore, though). The second majorpoint in the jig's favor, or so it seems to me, is the possibility of replication. You can make the joint, and come back a week later using the same settings and repeat the joint withint whatever fractional or decimal accuracy is possible with the unit.
Charlie Self "All you need in this life is ignorance and confidence, and then success is sure." Mark Twain http://hometown.aol.com/charliediy/myhomepage/business.html
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I wasn't doubting that it made them easier, I was just wondering about the strength. I've been using mortise and tenons in my furniture quite a bit lately and I was curious if I was fooling myself into thinking it was a stronger joint than it actually was. I just finished up a bed for my oldest daughter and am starting on one for my youngest and I was hoping my work would last long enough for them to be handed down once or twice.
snipped-for-privacy@aol.comnotforme (Charlie Self) wrote in

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"Jim" wrote in message

Obviously haven't lived long enough to see if my many M & T joints will stand the test of time, but I'd bet that most will, with one possible caveat - those in chairs.
Chairs in particular have a lot of stresses put on them, and antiique chairs have exhibited most of the M & T joint failures I've seen in furniture down through the years ... very likely a result of a combination of things besides the stresses, including the "glue" of the period, and the fact that with wood, which moves, joinery is never a sure thing. Inarguable manifestation of this observation is the cottage industry, of sorts, in the guise of the "Chair Doctor" businesses.
That said, I've rarely seen a chair from the same period with _pegged_ M & T joints that exhibits as much joint failure.
Strictly from this unscientifc observation, I'd infer that it may not be a bad idea to peg those M & T joints you suspect might not hold up. It is easy to do, can be a nice design touch, and was done quite frequently before the advent of relying strictly on glue.
FWIW ...
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For a great discussion of round tenons, check Hoadley's Understanding Wood.
For square tenons, as indicated, pegs which register the shoulder to the mortised piece are what the joint is about.

chairs
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That brings up an interesting point... How many of you folks routinely peg (Pin?) your M&T joints. I generally do, but I'm wondering if it's overkill.
Is there a reasony why pegs are not The RULE for chair joinery?
FWIW, My house has some 1860 vintage storm windows made with pinned M&T joints. Where there were failures, it was not the joint, but the wood itself that deteriorated due to 100 + years of harsh New England weather.
-Steve

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Probably because the joints are too small to pin without weakening them.
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"Stephen M" < snipped-for-privacy@primelink1.net> wrote in message
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Leigh
made
a
Depends partly on the glue you are going to use. If your are using aliphatic resin glues (TiteBond Yellow Woodworkers Glue, for instance), is is not gap filling. I will resist moisture better and hold stronger than hide glue, but if your joint doesn't fit, it won't improve your joint. Gorilla Glue, a polyurethane glue, purports to fill gaps, but the small print is that the gap filling property is a very weak foam. So, if your joints aren't well fitted, it's actually WORSE to use Gorilla Glue. Plastic Resin glues, as used by David Marks on Woodworks, dry very hard (and ridgid), are nearly waterproof, are gap filling, and have a very long open time. So, if your are going to make bad joints, this may be the stuff for you.
OTOH, you don't need an $800 machine, which BTW, requires another $150 - $350 machine to even make it work (the router). You can make perfectly good joints with hand saws, planes chisels, drills and such. You can also make perfectly good joints with just a tablesaw and a router. I saw a demonstration by Yeung Chan on Chinese joinery. He disassembles and reassembles a replica Ming Dynasty chair he made from a post card picture and knowledge of Chinese joinery techniques. All the joints in the chair but one he demonstrates in his book how to make primarily with table saw and router, with very little hand work. When reassembled, he sits in his chair and takes questions. No glue, no nails, no screws. Very solid. Important point - He contends that a joint should not be too tight, or there will be no room for the glue. That does not mean the joints fit badly, merely that you can slide them apart and back together by hand (if you can figure out which piece is not locked in by the other joinery). No malletizing required.
Cheers, Eric
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I looked at this jig pretty good before passing on it. Its price is just ridiculous when you look at other methods of making the same joint. A decent mortiser is anywhere from $175-250 and tenons are easily made on the table saw, router etc. I shop built a very very simple tenon jig that if all my tools and equipment worked as good as it does Id be delighted. Its just a right angle fixture that slides on my table saw fence with a toggle clamp. Took me about 20 minutes to build. That and a mortiser makes the joint quick and easy.
Jim

today
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You don't need to glue a tenon. If the joint is properly loaded, all it needs are a peg or two. Post and beam architecture, much less furniture, attest to this.
When designing, your assembly should stand, as it will, without glue or mechanical fasteners. Then the rest is gravy.

Leigh
made
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Most jigs are not devised to only make joints more precise, but for repeatability, and EASE most of all. Why would you want to spend more time making a joints thats sloppier than if you'd used the jig.
You can't afford NOT to buy that $800 contraption !
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Now that's just plain silly. If you aren't doing this for a living, I can think of a lot of things to do with $800. How about taking the family on vacation this year and getting some perspective on life in general. I would suspect the average audience in this forum is non-professional, so the jig has no way to pay for itself. That doesn't mean it's not worth the $800. It just means that it's not worth that much to me and a lot of other people. For a professional, it is quite possibly a serious time saver, and whether you like it or not we are all, in the end, paid by the hour. For a tool junkie, it's a status item. For an amateur whose more interested in the result than the journey, it may be worth the $800.
I, for one, CAN afford to NOT buy it.
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Well I do make my living doing this kind of work along with being a general contractor and builder of log homes. Cabinet work has been something I've done on and off for about 20 years now. Now I'm not stating that to say I've been doing it longer than anyone else. My point is that that overpriced jig is not that much faster to justify the cost. And if you know what you're doing you can make the joint just fine using one or more of many methods. I've seen the demos, I got the video and I watched and helped a fellow cabinetmaker use the Leigh. Its just not worth the cost. If it were to substantially add time or quality to my job then fine its justifiable. If it doesn't offer me either one of those things, its useless to me no matter what kind of tool it is.
Jim

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You must own one.

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Or work for the company.

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Dave, you OBVIOUSLY have not met either my wife or my wallet ;)
I agree that it would make the job faster, and if I did this for a living I could probably justify it. For the work I do though, I think it will be a long time before I can make the case to the CFO.
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I was joking of course. I agree with most of the posters that this can be done with basic home-made jigs. I would hesitate to pay $800 for anything without a power cord, even a miracle jig...
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Also, it stands to reason if you have one or two jobs to do, its never going to be worth the $800 jig. If I did this day in and day out, or made a living at fine furniture making, perhaps I'd throw down $800 for said jig... But for hobby use, my delta mortiser is plenty, and I can use the router, or bandsaw & chisels for the tenons.
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Jim wrote:

I'm biased, since I have the Leigh mortise/tennon jig. It is as good as advertised. I don't have a lot of time to handcut joints, nor do I want to settle for joints that are *almost* right. The Leigh jig makes it easy to make perfect mortise/tennon joints the first time. The manual that comes with the jig is excellent. Setup time is minimal. Repeatability is excellent. If you're serious about making mortise and tennon joints, you'll want to at least try out the jig. It comes with a thirty-day return priviledge.
(By the way, I have a Jet Mortiser, a Delta tennoning jig for my Uni-saw, and about a dozen jigs that I've made for my routers over the years. The Leigh Jig does the best job in the least amount of time.)
As far as a dramatically stronger joint is concerned. If you have the skills/tools to make a tight fitting mortise/tennon joint, then you've already achieved the ideal; however, if you need a tool that *helps* you make a tight fitting m/t join quickly and repeatably, without the need to clean-up with a chisel, consider the Leigh.
Mike
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