Mortise *or* tenon

[Deadeye]

I can cut really accurate tenons on the table saw... but then have to cut rectangular mortises.
Or
I can cut really accurate mortises with the router... but hen the tenons have to be round-ended.

Which is the lesser evil?

At the moment I'm favouring the router and rounding off the ends of the tenons.

 

[MikeG.]

Buy yourself a mallet and chisels, and you won't need to ask the question.

 

[Deadeye]

I've got a mallet and chisels. Slower.

 

[MattRoberts]

I'd always recommend cutting the mortises first, and then cutting the tenons to fit. Much easier to trim / sand a tenon to fit than a mortise, in my view

 

[custard]

Depends what you're making, but for many furniture scale M&T's you can drop a square ended tenon into a round ended mortice without suffering any serious loss of strength. If you think about it, the glue bond you'll get on the rounded end part of the tenon will be pretty crepe anyhow, so why bother?

If you're making something like a chair, where you need to squeeze every possible bit of strength out of your joinery, then just suck it up and put square ended tenons into square ended mortices, but for most everything else you can relax.

Incidentally, IMO consistently accurate tenons are harder to cut than consistently accurate mortices, so one resolution of the dilemma is to just follow whatever course of action gives you the best tenons.

 

[g7g7g7g7]

Split a dowel in half to fill the cavity?

 

[custard]

I'd always recommend cutting the mortises first, and then cutting the tenons to fit.

That certainly accords with the old furniture making advice..."first make the hole, then make the thing that goes into the hole".

The practical problem you run into when hand fitting tenons is this, once the tenon has been cut all the layout lines are lost, so how do you know where to remove material in order to get an acceptable fit?

On traditional carcase work you may be helped by having the rails set back about an 1/8" from the legs or stiles. But on more contemporary designs with flush aprons, or when making a cabinet door, you don't have that luxury. The worst outcome is if, during that tenon fitting process, you accidentally introduce a tiny bit of twist into the tenon, then you can easily end up with the entire cabinet door being in wind.

That's why I believe tenons are harder than mortices.

 

[Deadeye]

Depends what you're making, but for many furniture scale M&T's you can drop a square ended tenon into a round ended mortice without suffering any serious loss of strength. If you think about it, the glue bond you'll get on the rounded end part of the tenon will be pretty crepe anyhow, so why bother?

If you're making something like a chair, where you need to squeeze every possible bit of strength out of your joinery, then just suck it up and put square ended tenons into square ended mortices, but for most everything else you can relax.

Incidentally, IMO consistently accurate tenons are harder to cut than consistently accurate mortices, so one resolution of the dilemma is to just follow whatever course of action gives you the best tenons.

That's interesting - thank you. So is the strength primarily the glue? rather than the wood?
I ask because my current project needs to be dismantleable (if that's a word), so wasn't going to glue it.

 

[custard]

I ask because my current project needs to be dismantleable (if that's a word), so wasn't going to glue it.

Ah, well, that changes things a bit!

A square ended tenon in a round ended mortice will likely result in a bit of up and down float. So for "dismantleable" stuff (in the trade it's called KD or Knock Down furniture) you may well need a tenon that fits better on all four sides than would be the case with glued up work.

There's no point in being too prescriptive, a lot will depend on the particulars of your project and the tools you have at your disposal. But my initial position would be to cut round ended mortices with a router, cut the tenons to fit on your table saw, and round the ends with a file.

 

[sunnybob]

But if it needs to be KD, then how many KD's will it take to loosen the joint enough that its no longer strong enough for the job?

I freely admit I'm the worst "joint maker" on this site, but surely a bolted plate joint will be stronger in the long run?
I have a "oak furniuture land" type dining table with bolt on legs. Its 20 years old and has been disassembled at least 5 times. I doubt a M&T would survive that.

 

[ED65]

So is the strength primarily the glue?

Assuming a plain M&T (not pegged/dowelled, drawbored or internally wedged) the tenon is held in entirely by the glue bond, the majority of which is provided by the largest surface areas: the cheeks. So slipping a rectilinear tenon into a mortise with round ends doesn't matter that much. The joint is already stronger than it needs to be, assuming everything is done well naturally (tight fit, enough glue used), so this small loss is no biggie; if in doubt try pulling a test joint apart and seeing what happens!

As you're making something KD (knock-down) are you planning a tusk tenon, where a wedge or folding wedges hold the projecting tenon, or were you going to use a bolt?

 

[dzj]

"... but hen the tenons have to be round-ended"

Knock off the corners of the tenon with a chisel or rasp and make a card scraper
with a semi-circle. The diameter should be that of the mortising bit.
Pencil a center line on the tenon and when you reach it with the scraper, it's done.
For the odd m&t, a small shop might make, it's quick enough.

 

[Just4Fun]

But if it needs to be KD, then how many KD's will it take to loosen the joint enough that its no longer strong enough for the job?

You also have to consider how many times the piece needs to be knocked down. Is it KD for ease of initial transport to site, after which it will be undisturbed? Or is it a portable item that will be dismantled on a regular basis?

I have a "oak furniuture land" type dining table with bolt on legs. Its 20 years old and has been disassembled at least 5 times. I doubt a M&T would survive that.

It is an interesting question. I would contrast your table with some display cabinets that we have. I don't know how old they are because my wife owned them before we were married 30 years ago. They have been dismantled for 10 house moves, plus for various furniture re-arrangements & re-configurations. They show no signs of becoming loose even though they are only held together with dowels into veneered chipboard. Of course they are not subjected to the racking forces your dining table may have to face. So the nature of the piece and its use must also play a part.

 

[Phil Pascoe]

I only once went down the rounded tenon route (on a bench frame) and wished I hadn't. I'm sure it's far quicker and much more accurate to square the mortices.

 

[MikeG.]

I've got a mallet and chisels. Slower.

If you think squaring the rounded corners of a mortise, or rounding the edges of a square tenon is slow, then maybe woodwork isn't for you.

 

[thick_mike]

You neeed to build a pantorouter!

Pantorouter demo

 

[Deadeye]

So is the strength primarily the glue?

Assuming a plain M&T (not pegged/dowelled, drawbored or internally wedged) the tenon is held in entirely by the glue bond, the majority of which is provided by the largest surface areas: the cheeks. So slipping a rectilinear tenon into a mortise with round ends doesn't matter that much. The joint is already stronger than it needs to be, assuming everything is done well naturally (tight fit, enough glue used), so this small loss is no biggie; if in doubt try pulling a test joint apart and seeing what happens!

As you're making something KD (knock-down) are you planning a tusk tenon, where a wedge or folding wedges hold the projecting tenon, or were you going to use a bolt?

It's a bed frame - and I'm just a hobbyist so much of the technical talk in the thread ges past me. The joints need to be strong enough for 2 adults (who might not always be keeping still...) :wink:

 

[custard]

It's a bed frame

Blimey Deadeye, why didn't you say that in the first place!

Bed frames are almost always made knock down, because otherwise you couldn't get them up the stairs in most houses. Consequently there is a fairly unique form of joinery that's evolved just for bed M&T's. These specialist bed joints are simple to make and are well proven over time. Just Google "Bed Mortice And Tenon" or "Making Bed Joints" or something like that and it'll all be laid out for you. As far as furniture making is concerned beds really aren't that hard, and all the specialist hardware is cheap and widely available, stuff like this,

https://www.ebay.co.uk/i/202331295926?c ... 379&crdt=0

You can even do a quick and simple job with some hefty dowels (along with the above bolts) instead of M&T's, 16mm dowels are specially made mainly for beds, making your own dowel jig for this isn't particularly hard either,

https://www.ebay.co.uk/itm/HARDWOOD-MUL ... R_g0UZaIYg

 

[Woodmonkey]

See my purpleheart bed wip which I just bumped by accident, the bed bolt fittings are shown. Was trying to link to it but couldn't work out how.

 

[dzj]

Or do away with tenons all together.
Notch the posts to accept the bed rails or route a 1/2" deep mortise that will
fit the entire bed rail end. Some sturdy bed bolts and you're in business.