Double M&T Joints

[spadge]

Mr G,

I think loose tenons are definitely quicker to cut if you use a router and a jig (and have some made up loose tenons). The Festool Domino is just a refinement of this method and I can't see anybody cutting a tradition M&T as fast as that machine can make a joint.

Whether you should be using a machine instead of a saw and chisels is of course another debate!

Never thought of looking at a loose tenon as two M&T. It's a nice explanation of why the joint is weaker.

Cheers

Grahame

 

[Steve Maskery]

Well I just don't get it. Face-grain to face-grain glued joint is stronger than the wood itself, that's why the wood fails. So the only bit that is likely to fails is the cross-grain part, which, as Scrit points out, is the weakness of all M&T joinery.

Jacob is right about loose tenons being rare in trad joinery, but that's becuse it's easier to cut a tenon with a handsaw than it is to chop out a mortice with a chisel. We have easier ways of doing things these days, that's all. I really can't see a quicker way of cutting an accurate M&T joint than the Domino. Of course it has its size limitations, like all tools, but for me, it means that my joints are Right First Time Every Time (now where have I heard that before?). When I suggested loose tenons right at the start, I didn't realize that BB had a bench rail in mind. No, I wouldn't use them in that scenario, except perhaps as locators when the main strength was supplied by a dirty great big bolt. But for furniture-scale joinery they are great, especially as you can double them up just as easily, which is a very difficult joint to do by hand.

You do show some superb traditional joinery, Jacob, stuff I wouldn't attempt, but I do find your dismissal of everything modern difficult to understand. Being traditional is not essential.

Cheers
Steve

 

[Anonymous]

Byron

I never use a rod or batten as I come from an engineering background, l not woodwork. I tend to lay all legs (or whatever) side by side and mark together with a square and rule - will be exactly the same that way and it is even more accurate than a rod.

Also, you need to draw out the bench before starting. Even a simple drawing on A4 is worth its weight in gold, especially if marked up with little notes to remind you of key points

Steve
On your point to jacob about traditional joinery versus loose tenons from a Domino. Advocatinga machine that costs £500 (with the bits) just to cut for loose tenons? Seems like a very high price for a tool that only speeds mortising up slightly when compared to a router with a fence (surely every hobbyist has a router already).
Personally, I (like Jacob?) prefer to do things in a more traditional way and cut the tenon into one piece as time is not a priority for me (hobbyist) and I actually enjoy making the joints.

It is the processof the making that is where the enjoyment lies for me, particulalry cutting the joints, not just the final piece.

 

[Scrit]

Well I just don't get it. Face-grain to face-grain glued joint is stronger than the wood itself, that's why the wood fails. So the only bit that is likely to fails is the cross-grain part, which, as Scrit points out, is the weakness of all M&T joinery.

Yes, Steve, but what I said was that a traditional M&T has only one side of a joint to fail whereas a loose tenon has twice the potential failure area. There's also the issue of the material - aren't Domino biscuits made from beech, a material totally unsuited for exterior use?

Jacob is right about loose tenons being rare in trad joinery, but that's because it's easier to cut a tenon with a handsaw than it is to chop out a mortice with a chisel.

Machine mortise and tenoing has been around since at least the 1860s. Semi-automatic round-end mortisers and tenoners, a type of machine commonly used in chair making appeared in the early 1900s. Casein glues appeared before WWI and the earliest resin glues appeared before WWII. Yet for all that industry never adopted the loose tenon for solid wood products either. For sheet material there's a sort of yes because of the increasing use of multiple dowels from the 1930s onwards, but apart from chair making they are absent from almost all quality manufactured solid wood joinery to this day.

But for furniture-scale joinery they are great, especially as you can double them up just as easily, which is a very difficult joint to do by hand.

Ah, c'mon Steve, you just need more practice! :wink:

Steve

 

[Anonymous]

Incidentally the rod (by other names) is widely used in engineering and other trades, you obviously weren't paying attention :roll: Steel fabricators lay stuff out with chalk lines full size,

Ahh, I meant that I come from a precision engineering background. Very different approach.

 

[Johnboy]

I think Grahame came up with a good point. All the tests I have seen have been ultimate strength tests on new joints which all seem to show the glue joint is stronger than the wood. Why then in nearly all the joints that I have seen that have failed in service is it that it is the glue that has failed? I think it is because that in service the joints get continual small loads that fatigue the joint and make the brittle glue fail rather than the wood. No data to confirm this just based on my experience of testing automotive components where repeated application of service loads is used rather than ultimate strength tests. This often results in failure in unexpected places. Be very interesting if somebody (one of the mags perhaps) could do these tests. MIRA (motor industry research association) could do this but at a price.

John

 

[Scrit]

BTW though I say it myself, the rod and how to do it is probably the single most useful thing you could learn from the whole of this site, if you don't already know it.

Amen to that! Rods also have other uses, such as taking installation dimensions without the inaccuracies of measurement and calculation (kitchen/bedroom installations) and can be stored and retrieved for the future (useful if you want to install identical doors in a house over a 12 or 18 month renovation project but don't want to make and store the doors all in one batch).

Scrit

 

[Anonymous]

snip
Jacob is right about loose tenons being rare in trad joinery, but that's becuse it's easier to cut a tenon with a handsaw than it is to chop out a mortice with a chisel. We have easier ways of doing things these days, that's all. I really can't see a quicker way of cutting an accurate M&T joint than the Domino. snip

I bet my way is much faster - mortices with a mortice machine, tenons with band and/or table saw. What is a "domino" BTW? I bet it makes lots of noise and dust like a router and is similarly a PITA to use :lol:

You do show some superb traditional joinery, Jacob, stuff I wouldn't attempt, but I do find your dismissal of everything modern difficult to understand. Being traditional is not essential.

Cheers
Steve

Thanks for that Steve. No I don't dismiss everything modern - just almost everything. I just have a great respect for the golden age, the great tradition etc. and yes traditional is just about essential for quality woodwork IMHO

cheers
Jacob

 

[Steve Maskery]

Yes, Steve, but what I said was that a traditional M&T has only one side of a joint to fail whereas a loose tenon has twice the potential failure area.

This is my point Scrit. I don't think that is true, simply because face/face joints with a good glue are stronger than the wood, therefore it is not twice the risk. OK it's not, perhaps, zero risk, but minimal.

There's also the issue of the material - aren't Domino biscuits made from beech, a material totally unsuited for exterior use?

Now there you make a very good point we haven't covered. But loose tenons don't have to mean Domino, and slots cut with the Domino tool don't have to take beech dominoes, it's a doddle to run up miles of loose tenon stock. Half an hour in the workshop milling up scrap will yield enough stock to last me for yonks. I know it's different for a commercial enterprise, but I see things from the point of view of the home woody (OK a home woody privileged enough to own a Domino). Also I'm coming at this from the furniture-making perspective, not architechtural joinery exposed to the elements.

Ah, c'mon Steve, you just need more practice! :wink:

You've got me there, Scrit, can't argue with that one!
S

 

[ByronBlack]

I think for the price of the domino, I would rather spend the money on some quality hand-tools and some instructional courses/DVD's, or even a bandsaw

I'm with Jacob on the traditional side of things, I think there is something quite soul-less making furniture with almost all powertools - it's too easy, it's just assembly, with hand-cut joints you are adding soul and spirit to the piece. You're adding hardwork, concentration, and in my case; a learning process. As great as the domino is, for the home-woody, i think time/money can be better spent elsewhere.

Today, I shall be taking my rough sketches and turning them into a decent scale drawing and making a rod for the rest of the project. I think it's a good time to do it as all i've done so far is milled the wood, no joints have been cut yet, so it's a good time to re-evaluate and plan the next stage, appreciate all the help so far!

 

[JFC]

I also do what Tony does but i use the first part as my template so in effect it is a rod , just one that gets used as part of what i'm making .

 

[George_N]

What is a "domino" BTW?

A Domino is similar in use to a biscuit joiner, but uses a moving drill rather than a rotating blade. The name comes from the domino-shaped loose tenons that fit the sockets that the machine drills.

 

[Scrit]

What is a "domino" BTW?

A Domino is similar in use to a biscuit joiner, but uses a moving drill rather than a rotating blade. The name comes from the domino-shaped loose tenons that fit the sockets that the machine drills.

So it isn't a new brand of choccy biscuit, then? Oh, well......

Scrit

 

[Anonymous]

I just checked the price; £500+. Amazing. :shock:
You can buy real woodwork machinery at that sort of price, my morticer was only £600ish and it's a proper heavy industrial quality tool made of cast iron. And it will last forever.


cheers
Jacob

 

[Scrit]

.......and it's a proper heavy industrial quality tool made of cast iron. And it will last forever.

Ah, but it isn't green and black and emblazoned with the Festool name......

Seriously though, this is one tool I'm still not certain about, possibly because like you I've invested in static machinery and have the space for it, but for someone working in an 8 x 6ft shed it could have advantages - for one thing it is a heck of a lot smaller than a morticer. But for £500 you could actually extend the shed and buy a second-hand Sedgwick. Hmmmmm......

On the other hand if you start looking at ways of jointing boards I think the Domino might well be out-performed by either a biscuit jointer, a Duo-Dowler or even the humble black carcass screw - depending on the project, of course :wink:

Scrit

Who isn't sponsored by amyone, worse luck

 

[Anonymous]

I've done this once or twice - slotted screw joint. It's a bit of a fiddle but it makes a very strong joint, and need no special tools. Trad joinery as a whole needs no special tools - though there are things which can come in handy sometimes.

This sample I might not have discovered had it not been left in a damp cellar which softened the glue and then dropped on it's corner, which sprang the joint.

cheers
Jacob

 

[Benchwayze]

For my money, the weakest part of a traditional mortice and tenon is at the root of the tenon, especially if the worker has skimped on thickness. (one third was the rule I was taught).

I use slip-tenons a lot and I use marine ply for the tenons. I machine off runs of the most common sizes I use.

My jig for routing the mortices is just the fence that comes with the router. I lay the workpiece in the vice, so it projects far enough out to accomodate the router base. I always work from the face edge. Morticing the opposite end of the stile just means I pull the work along the vice, and machine the other mortice, on the other side of the vice, pulling the router toward me.

For morticing the rail ends, I do the same thing, but I mark the mortice with a gauge, and cut to the lines by eye, making sure I don't make the mortice too wide.

The largest bit I use is 1/2" (I don't do metric unless I have to.) If the mortice has to be wider I just make extra cuts after I have machined all round.

If I want to make side by side double M&T's, I complete all of the 'face side' mortices first then adjust the router, when necessary and repeat for the others.

I don't square off the mortices, but round the tenon stuff when I make it.

If I am going with hand work, then I stick to traditional methods, and usually employ through tenons and wedges. But that's another story, more suited to arts and crafts maybe!

John .

 

[spadge]

Spadge, have you got a reference for that, please, I'd like to look it up?
Thanks
Steve

Steve,

Have you ever heard the Alan Sherman record "Camp Granada"? Well like that record mother father kindly disregard my last post.

The test of comparative joint strenght is in FW no 111 (April 1995).
It compares loose tenons with trad M&T and double and treble biscuited corner joints. The strongest joint was the treble biscuit, next came the two biscuits and equal in strenght were the loose tenon and the trad M&T.
However, the biscuit joints failed completely whilst the loose tenon and trad M&T remained intact even after the joint had failed.

The loose tenon was voted the overall best joint but they stressed the importance of straight grain in all the joints.

So sorry for the misleading info, it's either my prejudices overcoming my memory or more likely just my age.

Grahame Allan, News at Ten, specialist subject, talking boll*cks

 

[JFC]

Did they knock the wedges back into the trad M&T and try again ?