Shouldering a Domino joint - worth the effort?

[smorgasbord]

EnCurtis has a video on making a shouldered domino joint:

It's a bit involved, requiring a jig to accurately cut the domino mortise in a dado, and then being able to cut the matching mortise in the true center of the end of the cross-piece.

The jig has a thickness, naturally, and so one has to compensate when setting the depth on the domino. And dado, too.

Matter of fact, he messed it up on his most recent video:=shared

And had to resort to making decorative mortise end fillers since he blew through the sides of his bookcase.

I get why shouldering the joint makes it stronger than just dominos. My question is under what circumstances is this additional strength needed/worth the effort?

I also think his jig would be better with the bushing option, as that would enable use of other diameter router bits to cut the dado, but I guess he's happy always doing ½" wide dados and cutting the shoulders as deep/shallow as necessary to have a ½" tenon (which he mills after cutting the domino mortises).

If you haven't watched either of these, watch the second one first, where he summarizes the jig and yet messes up. I like how honest he was about the mess-up and his solution, but again I'm wondering about whether I want to consider putting this into my joint repertoire. And if so, what better ways are there to machine it (using a Domino, of course).

 

[woodferret]

None.  Only time haunched tenon is useful is where there's a glueless expansion joint or weak glue line.  Think outdoor furniture and breadboards.  PVA glue is flexible, but limited in how much it can move before failure.  Like his explanation, the tenons and pegs provide the axial pull.  The haunch provides a bit of alignment in-between the tenons (because you can't have an infinite number of tenons).

But I think if you're dealing with outdoor furniture, thinking of unique ways to use the domino instead of concentrating on water ingress and pooling of the joints is misdirected effort.  And if dealing with breadboards, you're going to want a larger haunch.  The dado depth he uses... just stick another domino in there and call it a day.

 

[Crazyraceguy]

I saw that on YouTube this morning. I don't see it as beneficial in that particular case. The stub-tenons really only add "sheer" strength, not much against racking, like a deeper tenon would. As this unit was attached to a wall, racking is out of the picture.
The shoulders are really there to change the direction of the seam. If the tenon does not fit perfectly, it is never seen, which is part of why through-tenons are so much harder to make. Sloppiness of the fit shows.
The addition of the Dominos would do the same as a longer tenon. So why not just make a longer tenon?....since you are already set-up to cut them.
It would have been far easier to just build the thing with Dominos and be done. Both result in the same appearance, which is the same as a butt-joint. 

 

[ChuckM]

None. Snip.

Amen.

You can always complicate things or a joint for any reason other than strength. Some fancy hand-cut joinery does just that.

I've been re-watching New Yankee Workshop, and I can't but be reminded that Norm was able to finish so many different projects including a boat using just a few basic joinery, namely, M&T, dado, dowel, lap. miters, pocket screws, and biscuit (mostly for reinforcement). Of course, in his time, the Dominoes were not available yet.

 

[woodferret]

I'm kinda starting to understand the 'hate' towards the domino.  We did well without it.... same way I feel with a lot of YT jigs.  But I think the difference was that the DFXXX made what we did, easier, faster and with less F-ups.  Who hasn't cut a board with a tenon short? 

These jigs (and techniques) however, seem to be searching for a problem to solve.  It's nothing really new with YT though, as these always cropped up in the 'letters' section of the older mags.

Now, on to the Mafell NFU50.... now that's the way to make these haunched tenons - 100% more hamster bedding, 50% of the time

 

[smorgasbord]

I don't see it as beneficial in that particular case. The stub-tenons really only add "sheer" strength, not much against racking, like a deeper tenon would. As this unit was attached to a wall, racking is out of the picture.

OK, what about the case of a bookcase, where you're joining shelves to the sides in a "T"?

If you use just the dado, you get support across the whole width of the shelf, but not much on "pull-out," which maybe isn't needed unless there's so much weight the vertical sides bend.

If you use just the Domino, you get support whereever there are dominos, so mostly across the width of the shelf. But, now you're dependent on the sheer strength of the domino itself. How many 6mm dominos does one need to support a 3' wide shelf of heavy books?

Of course, the answer in my household is "Who buys physical books anymore?" We stopped about 10 years ago and read everything digitally now.

On a side note, I still think that for 18mm-19mm stock a 7mm domino would be best. But, I'm in the minority on that one.

 

[woodferret]

But, now you're dependent on the sheer strength of the domino itself. How many 6mm dominos does one need to support a 3' wide shelf of heavy books?
...

Festool Aus.
[attachimg=1]

6mm = 220kg
Weight of a casebound book ~1kg to 3kg.

So that'd be 73 of the hardiest tomes a 3' shelf, assuming all load is on the single tenon.  For engineering's sake, let's say 1/3 of the load per tenon assuming tripod load distribution so we'd probably be able to hold ~200 medical books per shelf.  I think you're safe.

 

[luvmytoolz]

When I built our 2.4m high corner units one bookshelf was 1m wide and the other is 1.5m wide, both are 300mm deep and hold at least a couple thousand books by my rough estimate. As we double stack our books there was no way I was end joining 19mm thick boards without a 3mm deep dado for them to sit in for additional strength.

The sheer load for a bookcase isn't just about the amount of weight a Domino tenon can support, the strength factor of the shelf not breaking at the tenon joint is also a big consideration in this case.

 

[ChuckM]

Snip.
On a side note, I still think that for 18mm-19mm stock a 7mm domino would be best. But, I'm in the minority on that one.

If one has trust in the Festool manual, 8mm is the common choice for 19mm hardwood (and 6mm for plywood). Yes, I have more 8mm tenons than 6mm in my inventory because most of my projects are done in hardwood:

[attachimg=1]

 

[ChuckM]

Snip.
The sheer load for a bookcase isn't just about the amount of weight a Domino tenon can support, the strength factor of the shelf not breaking at the tenon joint is also a big consideration in this case.

The back board, if there's one, will matter significantly in preventing racking, which in turn, has a huge bearing on the shelf joinery too.

 

[ChuckM]

His approach kinda reminds me of some users who insist that mortises be milled in the (dead, more or less) center of the work. I could only think of two scenarios in which the extra work of achieving centerness makes sense:

1) When you try to use the 4mm tenons on 5mm plywood or stock
2) You're doing exposed joinery on the edge (for whatever reason), and you want the tenon ends to look nice in the center.

I'm afraid that, like this shouldering thingie, all the extra effort spent on dead-centering mortises on 3/4", 1/2" or any other thicknesses carries no material value. Of course, it's not a right or wrong matter as long as one enjoys the time spent. We may have the same tool, but we are free to use it the way we love to.

 

[luvmytoolz]

I almost never dead centre anything, makes things way too tedious and increases the risk of a stuffup dramatically I reckon. Referencing off the same plane face using a default setting is all I do pretty much always.

 

[jujigatame]

EnCurtis has a video on making a shouldered domino joint:

It's a bit involved, requiring a jig to accurately cut the domino mortise in a dado, and then being able to cut the matching mortise in the true center of the end of the cross-piece.

The jig has a thickness, naturally, and so one has to compensate when setting the depth on the domino. And dado, too.

Matter of fact, he messed it up on his most recent video:=shared

And had to resort to making decorative mortise end fillers since he blew through the sides of his bookcase.

I get why shouldering the joint makes it stronger than just dominos. My question is under what circumstances is this additional strength needed/worth the effort?

I also think his jig would be better with the bushing option, as that would enable use of other diameter router bits to cut the dado, but I guess he's happy always doing ½" wide dados and cutting the shoulders as deep/shallow as necessary to have a ½" tenon (which he mills after cutting the domino mortises).

If you haven't watched either of these, watch the second one first, where he summarizes the jig and yet messes up. I like how honest he was about the mess-up and his solution, but again I'm wondering about whether I want to consider putting this into my joint repertoire. And if so, what better ways are there to machine it (using a Domino, of course).

My favorite part of the whole video was when his mom walks in and she says, "That's beautiful, but OH WOW, YOU PATCHED THE HOLE IN THE DRYWALL!!!"

Exactly how my mom would react!

 

[alltracman78]

Maybe I'm missing something, but I don't see the need for a jig to make this joint?
Seems like extra work for no purpose?
Putting aside whether it's useful or not.

Why wouldn't you use the same technique as for a regular shelf?

Cut your dados and shoulders.
Assuming everything is identical "install" one of the shelves into your dado.
Correctly orientate the shelf you want to mortise, then lay against the "installed" shelf.
Clamp the shelf to be cut.
Remove "installed" shelf.
Cut mortises with the normal technique.

If you only have one shelf, cut a thin jig shelf to use as a guide.

The only change would be adjusting the depth of the dado mortise.

And if you want through mortises, do your cuts, lightly mark center of dado on the outside, install and clamp shelves, then cut through both together.

 

[derekcohen]

'''
I get why shouldering the joint makes it stronger than just dominos. My question is under what circumstances is this additional strength needed/worth the effort?
...

Housing ensures:

1. the shoulders are covered and the joint is neat.

2. a shallow housing provides extra strength as it has a ledge upon which the shelf rests.

A simple Dominoed joint (that is, no housing) will be weaker and the shoulders will show once the wood moves (moisture and dryness in the air will do this).

An alternative is a tapered sliding dovetail. Best of all!

Regards from Perth

Derek

 

[smorgasbord]

Housing ensures:

1. the shoulders are covered and the joint is neat.

2. a shallow housing provides extra strength as it has a ledge upon which the shelf rests.

A simple Dominoed joint (that is, no housing) will be weaker and the shoulders will show once the wood moves (moisture and dryness in the air will do this).

1) A simple "T" butt joint is about as neat as one can get, and has the advantage of simplicity in achieving that neatness.

2a) Upthread has established that any additional strength over a dominoed T joint is either minimal or not needed.

2b) Actually, I believe the shouldered joint will be more prone to gaps due to wood movement! A simple "T" butt joint that has the grain running in the same direction should have both boards expand and contract in width the same.

But, the shouldered joint has the potential for the horizontal shelf to get thicker or thinner with moisture changes, while the vertical piece, the one that has the dado, will not have any wood movement in the width of the dado. This probably won't be visible 4/4 stock, but in large 8/4 or especially thicker pieces the differences could create gaps. The non-shouldered assembly might see the shelf get thicker or thinner, but that would just expose less or more of the vertical piece - the shelf won't pull away from the vertical due to wood movement. But, the shouldered joint could see the shelf get thicker or thinner while the dado width won't change, thus potentially creating a gap. Yeah, a small gap to be sure, but there's more potential there than with the simpl domino-reinforced butt joint.