# Wedged through M&Ts



## dunbarhamlin (1 Aug 2007)

Watched Mr Cosman's M&T DVD last night. Got me thinking. Any rules of thumb for when you'd bore through the bottom end of the kerf-for-the-wedge as a split inhibitor?

(Got a little something from Mr Iles too - can report that lapping D2 not a problem)

Cheers
Steve


----------



## Sgian Dubh (1 Aug 2007)

dunbarhamlin":1e8291im said:


> Any rules of thumb for when you'd bore through the bottom end of the kerf-for-the-wedge as a split inhibitor? Steve



Always. Slainte.


----------



## ByronBlack (1 Aug 2007)

Steve from what i've read, you make the hole a mm or two larger than the kerf to accomodate the width of the bottom of the wedge. I'll be doing this very joint soon - hoping not to pipper it up


----------



## dunbarhamlin (1 Aug 2007)

Thanks chaps
That's what I thought, though in the vid no hole is used. The kerfs are instead cut on the slant finishing just shy of the edge. Different sort of a joint I suppose
Cheers.


----------



## woodbloke (1 Aug 2007)

I've recently cut a whole load of these and I think that you need to be quite careful how you produce them. The saw cut for the wedge I make parallel to the side of the tenon and ending about 6mm from the shoulder, no hole at the bottom to prevent a split (tho' this is a good idea). The mortice is made about 3mm wider that the tenon so that it's splayed into it by the wedge. However the_ critical_ thing is in cutting the wedge as ideally it needs to come to the bottom of the saw cut and at the same time, push the tenon to the outside of the mortice but unfortunatly it's not something that you can do a trial run on as once the wedge(s) have been tapped home it's almost impossible to get the joint apart again. It would be a disaster if the wedge reached the bottom of the saw cut but didn't push out the tenon to the edge of the mortice, ie the wedge has been cut too thin:







These particular ones were left higher than the surrounding leg so that they could be shaped:






What I would recommend is a trial joint to get the proportions of the wedge and mortice exactly right before the real thing is attempted, beware tho', it's quite tricky to get it bang on  - Rob


----------



## ByronBlack (1 Aug 2007)

Hi Rob,

Thanks for the detail and the pics! I like the shaping, very attractive joint. How do you work out the size of the wedge? And finally - do you slope the mortice to match the angle of the wedged tenon, or do you keep the sides parallel?


----------



## dunbarhamlin (1 Aug 2007)

Wow - thanks Rob.
Good job I'm in gung ho mode - the sight of work like that could put me off even trying to replicate in a more realistic frame of mind 
Cheers
Steve


----------



## woodbloke (1 Aug 2007)

BB - saw cuts are kept parallel tho' some people make the saw cut angled....I don't think it makes a lot of difference really. To get the right proportions for the wedge needs a little bit of guesstimation and trial and error. What I did on my practice joints was to make the wedges about 100mm long so that when they're tapped home you at least have got something to hold onto to try and wiggle the damn things out again but it ain't easy. You can also (again on the practice joint) bang in the wedges dry *without* putting it into the mortice. It's then easier to see if the wedge(s) comes to the bottom of the saw cut and at the same time to measure the deflection of the tenon side to see if it's splayed enough. As an example, say tenon width is 40mm, mortice width is 44mm (2mm splay each side) then when the wedges have been tapped home the width across the top of the tenon _ought_ to be a fraction more than 44mm (to ensure a tight fit). Hope this makes some sense  as this is just the way I worked out how to do it so that the joint looked half decent as the aim I think is also to get both the wedges the same thickness at the top - Rob


----------



## Scrit (2 Aug 2007)

woodbloke":zp9vt4jg said:


> BB - saw cuts are kept parallel tho' some people make the saw cut angled....I don't think it makes a lot of difference really.


If you angle them you'll end up with short grain and that weakens the tenon

One thing people sometimes forget is to leave 1/4in or so at the shoulder end of the mortise as a straight piece to guide the tenon into the mortise

Scrit


----------



## David C (2 Aug 2007)

Scrit,

Alan Peters used angled sawcuts if the timber was very hard and brittle.

I assume that he thought , that if the glue joints were good there would not be an appreciable loss of strength.

Would like to confirm Rob's observations, that wedged tennons need careful working out and testing.

Many factors to consider;
saw kerf,
tightness of tennon before kerfing,
compressibility of timber,
things swell up with water based glues,
taper on wedges,
accuracy of wedges,
etc, etc.

Don't let me put you off though!

David Charlesworth


----------



## ByronBlack (2 Aug 2007)

:shock:


----------



## Scrit (2 Aug 2007)

Hi David

I have to admit that many of the joints I've wedged have been in softwoods and I've just followed the practice I was taught without thinking much about it

One thing about woodworking is that you never stop learning  

Scrit


----------



## David C (3 Aug 2007)

That's why it will always be fascinating!

David


----------



## ByronBlack (3 Aug 2007)

I'm still a little confused on one issue.

Should the mortice be tapered to accomdodate the new angle of the tenon that is produce by the splaying from the wedges? Or should the mortice stay square?

I've got two books, both showing different ways. Personally, it's seems logical to taper the mortice to accept the splayed tenon and thus achieving a kind of dovetail effect... any thoughts?


----------



## woodbloke (3 Aug 2007)

BB - to clarify. The tenon is of course cut with parallel sides and parallel saw cuts (or sloping) ending about 6mm from the shoulder line. I always cut parallel saw lines 'cos it's easier. The mortice face adjacent to the tenon shoulder is the same width as the tenon, but the top face of the mortice that shows is wider by a couple of mm (or however much you want to splay the mortice, I wouldn't recommend more than 2mm _each_ side) so this needs to be chiseled out after the main mortice has been cut. The mortice as a sectioned view would look like the bottom half of an isosceles triangle with the top cut away. Has the mud cleared and been replaced by sparking waters?.......probably not, it's me not you :lol: - Rob


----------



## Scrit (3 Aug 2007)

The mortise should be tapered to accommodate the extra material of the taper. Here's a drawing of a foxed tenon which should help explain it:






The tapered wedge is made to fit snugly

OK so these are not through tenons, but the principle is the same.

Scrit


----------



## ByronBlack (3 Aug 2007)

Rob, Scrit - Thank you both, that makes perfect sense! I best mill up some stock for some test cuts!


----------



## Anonymous (6 Aug 2007)

BTW the "foxed" tenon is a way of getting a very firmly keyed fixing in a stopped mortice. For a through mortice a foxed tenon is used decoratively, but is likely to be weakened by virtue of the bending outwards of the tenon edges and risk of breaking. Normal edge applied wedges are going to be stonger and easier to perform.

cheers
Jacob


----------



## bugbear (6 Aug 2007)

Mr_Grimsdale":stmkcth0 said:


> BTW the "foxed" tenon is a way of getting a very firmly keyed fixing in a stopped mortice. For a through mortice a foxed tenon is used decoratively...



I thought the term "fox wedging" ONLY applied to stopped mortices, the implication being a hidden/sneaky method.

Surely a through tenon treated this way is simply a "wedged tenon".

BugBear


----------



## woodbloke (6 Aug 2007)

Bugbear wrote:


> I thought the term "fox wedging" ONLY applied to stopped mortices, the implication being a hidden/sneaky method


It does. If you miscalculate with fox wedged m/t's they are almost *impossible* to get apart - Rob


----------



## bugbear (6 Aug 2007)

woodbloke":6js3dd7w said:


> Bugbear wrote:
> 
> 
> > I thought the term "fox wedging" ONLY applied to stopped mortices, the implication being a hidden/sneaky method
> ...



Dry fitting to test not recommended, I gather  

BugBear


----------



## ByronBlack (6 Aug 2007)

Mr_Grimsdale":3vpcphjj said:


> BTW the "foxed" tenon is a way of getting a very firmly keyed fixing in a stopped mortice. For a through mortice a foxed tenon is used decoratively, but is likely to be weakened by virtue of the bending outwards of the tenon edges and risk of breaking. Normal edge applied wedges are going to be stonger and easier to perform.
> 
> cheers
> Jacob



I have to disagree. In Percy Blandfords 'Practical Carpentry' it states:

"Through tenons may have wedges driven outside them. This tigtens by compressing the tenon, which is not as efficient as spreading it."

It also goes on to explain about 'fox' wedges being applicable only to stubb or blind tenons.

OOh, get me: qouting from a book! :lol:


----------



## dunbarhamlin (6 Aug 2007)

This has been super informative - thanks to all - far better than a frozen reference, whatever the author, as we're getting a melding of styles and ideas from different areas of applied joinery.

Talk of foxes in the same breath as through tennons made me wonder, do blind M&Ts ever get used with a through wedge? By which I mean sort of a fox tenon, but with a square sided through mortice to allow pegs, wedge shaped on their inner part, to be driven into the joint from the other side, so only the wedge is visible on the outside. Don't expect it would have any benefits, but just might be fun as a design element.

Cheers
Steve


----------



## woodbloke (7 Aug 2007)

BB wrote-


> It also goes on to explain about 'fox' wedges being applicable only to stubb or blind tenons.


which is what I was referring to as in Scrit's diagram. Fox wedged tenons is the term used when blind tenons are wedged and the wedges can't be seen when the joint is driven home - Rob


----------



## Anonymous (7 Aug 2007)

ByronBlack":2sa1s52z said:


> Mr_Grimsdale":2sa1s52z said:
> 
> 
> > BTW the "foxed" tenon is a way of getting a very firmly keyed fixing in a stopped mortice. For a through mortice a foxed tenon is used decoratively, but is likely to be weakened by virtue of the bending outwards of the tenon edges and risk of breaking. Normal edge applied wedges are going to be stonger and easier to perform.
> ...


OK then whatever you call them - the wedges tapped into saw kerfs; yes, make a tight locked joint but fail due to likelihood of breaking. I know this having seen it on failed joinery ocasionally - the tenons drop out in 2 pieces.
The ordinary through wedged tenon is just about indestructible unless acted upon by external forces such as weather and poor maintenance.
An odd thing is that if not painted and subject to seasonal wetting and drying, then wedges and also dowels through tenons, once the glue is loosened, will work their way right out very slowly, by a sort of slow ratchet action. The dowels too are tapered i.e. square dowels knocked into round holes, which gives them a taper.

cheers
Jacob


----------



## Scrit (7 Aug 2007)

woodbloke":1t14w9bf said:


> BB wrote-
> 
> 
> > It also goes on to explain about 'fox' wedges being applicable only to stubb or blind tenons.
> ...


The diagram happened to be one I had to hand - and I was given to understand that the wedged tenon is a foxed tenon. whilst a wedged through tenon is just that, a wedged through tenon. Sorry if I (unintentionally) misled anyone, the diagram was the only one I had to hand at the time to explain the need for a straight "neck" to the mortise and the way in which wedges work.

Scrit


----------



## Paul Kierstead (7 Aug 2007)

This discussion is wonderfully confusing. I am expecting that some of the "wedged" tenons being spoken of here are what we might called pinned tenons or perhaps more specifically draw-bored pinned tenons.

Mr. Grimsdale, I don't think wedged one are inherently prone to breakage, it is just that they might be easy to make poorly.


----------



## Anonymous (7 Aug 2007)

It started off with Steve's "wedge into saw kerf" M&Ts as per Rob's very nice examples earlier. Not the same as the more usual "wedges in the side of mortice" (no saw kerf).
I just mentioned pins to confuse everybody!
BTW I don't think the hole as split inhibitor would work as the grain carries the stresses around the hole, unlike a homogenous material such as perspex.

cheers
Jacob


----------



## ByronBlack (7 Aug 2007)

Paul, pinned and draw-bore an entirely different beast - using dowels to mechanically fasten through the tenon rather than increase external resistance via a wedge. Good thread though!


----------



## Paul Kierstead (7 Aug 2007)

ByronBlack":30wvpfec said:


> Paul, pinned and draw-bore an entirely different beast - using dowels to mechanically fasten through the tenon rather than increase external resistance via a wedge. Good thread though!



Well, yes. 

The problem was, I did not even remotely understand:



> The ordinary through wedged tenon is just about indestructible unless acted upon by external forces such as weather and poor maintenance.



as being different from the diagram. Only just now I think I figured out that he was talking about wedges driven in the direction of the long grain (of the tenon), but alongside rather then into the long grain. Without figuring out that, the discussion was extremely confusing, especially calling this sort "ordinary", whereas around there they would be very very rare and ordinary would be the sort driven into a saw kerf. Doh. This is a case where a single diagram would have greatly clarified things.


----------



## Anonymous (8 Aug 2007)

Paul Kierstead":1o76ory1 said:


> snip
> Only just now I think I figured out that he was talking about wedges driven in the direction of the long grain (of the tenon), but alongside rather then into the long grain. Without figuring out that, the discussion was extremely confusing, especially calling this sort "ordinary", whereas around there they would be very very rare and ordinary would be the sort driven into a saw kerf. Doh. This is a case where a single diagram would have greatly clarified things.


Right, I didn't know that; it would be confusing, sorry.
Wedges in saw kerfs are very rare in my experience infact I've hardly ever seen them done like that except as decorative feature like Rob's examples. I've found them ocasionally in joinery work but usually I think they were hammered in as an afterthought when somebody had forgotten to cut the sloping sides of the mortice.
So that's the norm in Canada? In ordinary joinery too or just cabinet making?

cheers
Jacob


----------



## andy king (19 Aug 2007)

I was taught that in joinery the wedges are applied to the outer faces of the tenon, putting it in compression. The split tenon with the wedges in kerfs was discussed, and we were told because joinery tends to be heavier duty pieces of work, the joints need to be firmly locked, and if a kerfed wedge was applied, it was all to easy to drive them ovely deep and in doing so, split the rail.
The other consideration with external wedges is that the joints can be knocked up tight to shoulderlines which, if your initial setting out and cutting is sound, should ensure a square joint, but its still good practice to check the diagonals etc.
The principle is to glue up and push the wedges in finger tight, then tap the very outer wedges in lightly, forcing the rails up tightly to the mortice shoulderline, before driving them all fully home. Middle rails still need to be positioned to marked lines, and knocking the top and bottom rail wedges to drive the rail up tightly to the mortice shoulder only moves it by a fraction of a millimetre (unless your mortice is cut too wide!) but it's good technique.
If you have a deep bottom rail with twin tenons, the principle is still the same, tapping the outer ones in first, so if the right hand wedge is the outsde one, the other righthand one on the second tenon gets tapped as well to nudge the joint. (does this make sense?)

Hope this helps.

Andy


----------



## David C (20 Aug 2007)

Yes,

Joiners and cabinetmakers have different techniques.

David Charlesworth

Big thanks to Charley, a bit more signal and bit less noise would be most welcome.


----------



## Jake (20 Aug 2007)

David C":1kfns3w6 said:


> Big thanks to Charley, a bit more signal and bit less noise would be most welcome.



The thing is this isn't a book, or a lecture or a tutorial, it's a discussion forum and it encompasses all sorts of characters and views, and if it doesn't, it loses something - even if individual members are relieved not have to have those views shoved in their face. One man's noise may just be another man's iconoclasm.


----------



## David C (20 Aug 2007)

Jake,

Good point, mine was not aimed at anyone in particular!

best wishes,
David


----------



## j (21 Aug 2007)

Scrit":16ua45z8 said:


> The mortise should be tapered to accommodate the extra material of the taper. Here's a drawing of a foxed tenon which should help explain it:
> 
> 
> 
> ...



Just incase anyone didn't get how that works, there's a video demo in episode 2613 on this page.

J


----------



## David C (22 Aug 2007)

Jake,

Iconoclasm;

Act of breaking images: opposition to image worship.

Iconoclast; one who assails old cherished errors and superstitions. (Chambers)

The latter would definitely seem to be signal not noise?

David C


----------



## Jake (22 Aug 2007)

David C":2ou5afdh said:


> The latter would definitely seem to be signal not noise?



I'll counter your Chambers with a Concise OED:
_iconoclast / 'knklast/

→ n. 
1. a person who attacks cherished beliefs or institutions. 
2. a person who destroys images used in religious worship, especially one belonging to a movement opposing such images in the Byzantine Church during the 8th and 9th centuries.
- *DERIVATIVES iconoclasm n.* iconoclastic adj. iconoclastically adv. 
- ORIGIN C17: via med. L. from eccles. Gk eikonoklasts, from eikn ‘likeness’ + klan ‘to break’. _

So I guess that if the iconoclast isn't perceived as noise, nor is his iconoclasm.

As to definitiveness, well, in the general, and if it is true at all, then one man's iconoclasm is equally capable of being another man's noise, which is unfortunate - but I don't think it means we should shoot everyone we each perceive as an iconoclast in order to shut them up. Put some earplugs in, or ignore them or something.


----------



## ByronBlack (22 Aug 2007)

Getting back to subject for a second. Is there a definitive angle that should be used for the wedges? Does it have a big impact, or is it a case of just guessing a suitable angle?

And finally, does the wedge always have to be a harder timber? For instance, I wish to use Walnut wedges in beech tenons - is that a no go?


----------



## woodbloke (22 Aug 2007)

BB - glad to get back on topic....getting a bit lost amongst all the clever words :? Here's a pic of the spare wedges I cut for the Elm Chest a while back, you can see the sort of angle I used for them. These are in ebony and I would always use a harder, close grained, timber for the wedges if possible as they are less likely to deform as they are tapped home...no excessive force should be needed if you've got all the sums and measurements correct :wink:






Hope of some help - Rob


----------



## ByronBlack (22 Aug 2007)

That does help a bit Rob, thanks for posting that. Much apprecited. Would rosewood be hard enough to wedge beech do you think?


----------



## woodbloke (22 Aug 2007)

BB - I would have thought rosewood more than adequate for the wedges. Might be worth degreasing them with a bit of acetone (from LLoyds chemist) before gluing as it can sometimes be a bit greasy - Rob


----------



## andy king (22 Aug 2007)

Hy Byron,

I was taught (as a joiner) that you work to a one third, two third ratio, much the same as the mortice/tenon/shoulder ratio. (bearing in mind my previous post of external wedging, not kerfed)
So for example, a door rail of 95mm finished width would have a wedge taper chopped into the mortice two thirds deep, or approx. 60mm deep, the width at the top being about 10-12mm. This give a ratio of around 1:6, so introducing dovetailing parameters once the wedges are driven home. Don't know whether this is relevant for kerfed or cabinetry tenons, but the principle meets traditional angles and ratios used in both.

hope this helps.

Andy


----------



## andy king (23 Aug 2007)

Following on from this, I was also taught that a kerfed wedge for structural purposes rather than decorative is likely to fracture the thinner outer edge of the tenon once the wedge is driven, as it will snap at the bottom of the cut as it is forced over. On cabinetry this is not such a problem, but one heavier joinery applications, the strength and integrity of the joint can be compromised. Not such a problem in flexible, forgiving timbers as they should flex to accomodate the forces involved but brittle hardwoods are more likely to sucuumb, hence the outer wedging of joinery rather than the decorative wedging of cabinetry.

Andy


----------



## ByronBlack (23 Aug 2007)

Rob, Andy - thanks for that, much appreciated.

So, Andy, if you were making a heavy duty pair of trestles for a workbench out of beech, would you use kerfed wedges or outside wedges to join the trestle top to the trestle legs?


----------



## andy king (23 Aug 2007)

Hi Byron,

I would still go for an outer wedge, although if the top is say a 100x50mm on its flat, so the wedging depth is only about 30mm, I might consider a kerfed one, although i would more than likely not even use a tenoned set up and go for a splayed housing the same as a sawing horse, using a shouldered joint below the 100x50mm for support.

Hope this helps.

Andy


----------



## ByronBlack (23 Aug 2007)

Cheers Andy, much appreciated, I'll have to have a think on this. It will however have been a tenon setup as I've already cut the mortices; so I just need to decide to go for internal/external wedges.

To connect the trestle foot with the legs, i'll be using bore-drawed tenons whic I assume will be ok


----------



## Paul Kierstead (23 Aug 2007)

I'd admit I have never tried the outside wedges, but have used the kerfed ones a few times. One of the great advantages of the kerfed wedges is that the joint is self-clamping. It would _seem_ to me that outside wedges would tend to drive the tenon back out of the joint rather the pull it up snug. Now I gotta figure people wouldn't use it if that was the case. What am I missing here?

Incidentally, the Autumn 2006 edition of _Woodworking Magazine_ had an extensive article on the "kerfed" method. In the woods they used (can't recall which ones right now), splitting of the tenon was not an issue in a well formed joint. It is an interesting read. I don't doubt that in very brittle woods the situation might be different.


----------



## andy king (23 Aug 2007)

Hi Byron, 
The use of drawboring for tenons is usually reserved for situations where you can't get clamps on successfully or easily, such as newel posts.
A dowel through the mortice to pin it is often seen though, usually in situations where the removal of a horn leaves a bridle joint or a very short piece of end grain. I would opt for clamping up and simply drilling a hole clean through the joint and driving a glued dowel through. 
In painted situations the alloy star dowel was always a favourite, but I haven't seen these for years. I suppose they are still out there somewhere!
Paul, the outer wedged method doesn't drive the joint apart, it simply knocks it sideways, tightening the tenon against the mortice wall. Once they are driven home they compress the outsides of the tenon, so that in theory, should the timber dry out beyond its original moisture content, the fibres should re-expand and remain tight in the joint.
You need to have your sash clamps on first of course, but these only need to nip the joint up, as is the case in any joint. 

Hope this helps/makes sense!

Andy


----------



## woodbloke (23 Aug 2007)

BB - Andy is quite correct on draw boring as this method is used when there's not enough room for cramps. The two holes are offset tho', the hole in the tenon is closer to the shoulder line than the mortice hole by about 1mm or so (depending on the timber) and the peg is usually riven and very slightly tapered so that as the joint is tapped together, the wedge action of the tapered pin and the offset holes bring the shoulder lines up tight onto the mortice edge - Rob


----------

