Drawbored vs Through-Wedged Mortice & Tenon

[anaminal]

Morning All,

I've just learned about drawbored mortice and tenon in the topic below (cheers Pete M).

I've been using Mortice and Tenon joints for the last few months but have been securing them using a two through-wedges. These feel pretty secure but I really want my joints to be as strong as possible. Does anyone know of any comparisons that have been done between the strength / longevity of these two joints or any comparison of the two? Also if there are any other variations on the Mortice and Tenon I might be unaware of?


Thanks,
Chris

[forum mentioned]
onstruction-tips-for-gate-t70371-15.html

 

[marcros]

I don't know of a comparison on strength, though there will be one. Both are strong joints but I would expect the wedged one to be stronger because it is mechanical- like a dovetail. The tenon cannot come out unless it shrinks.

 

[anaminal]

...particularly, I am concerned about forces applied at 90 degrees to the joint as I used it when I made myself a pair of tonfa for martial arts (like a police baton). There are quite a few designs out there with regards to shape/weight of the length, but the handle really makes or "breaks" this item and I've found very little said about it.

 

[JakeS]

I'm no expert, but my expectation would have been that a drawbored M&T would be more or less as resistant to coming apart as a wedged one, since it's also mechanically locked in place... but probably not so resistant to becoming wobbly if the tenon wasn't a totally snug fit in the first place. Wedging makes the tenon actually physically larger inside the mortice and therefore has less space to wobble, while drawboring just forces it further inside the mortice.

For your tonfa, though, I'd worry that drawboring would also weaken the wood itself and make it more likely to split. Which doesn't necessarily mean "likely to split", just increase the risk as you need to cut two lateral holes in it parting the grain in two axes, rather than just one for a regular mortice. And then you whack a dowel through it, putting lateral pressure on the part of the grain that you drilled through!

 

[marcros]

http://en.wikipedia.org/wiki/Tonfa

If the joint was nice and tight, I dont think that you will have an issue. I think that I would have used wedged here too. I think that it would be a bit small to drawbore, the tenon must only be about an inch wide, and you would have to use 1/4" dowel I would think.

Both methods would likely work, but i think that you chose the better.

 

[marcros]

I'm no expert, but my expectation would have been that a drawbored M&T would be more or less as resistant to coming apart as a wedged one, since it's also mechanically locked in place... but probably not so resistant to becoming wobbly if the tenon wasn't a totally snug fit in the first place. Wedging makes the tenon actually physically larger inside the mortice and therefore has less space to wobble, while drawboring just forces it further inside the mortice.

For your tonfa, though, I'd worry that drawboring would also weaken the wood itself and make it more likely to split. Which doesn't necessarily mean "likely to split", just increase the risk as you need to cut two lateral holes in it parting the grain in two axes, rather than just one for a regular mortice. And then you whack a dowel through it, putting lateral pressure on the part of the grain that you drilled through!

I did read somewhere that on drawbored joints it was not vital if it was a bit sloppy (within reason), as long as the shoulders were tight. I guess that the drawboring pulled the joint in, and in theory the tenon in the joing can do what it likes, because it cannot move anywhere. I presume taht this required a minimum of 2 dowels, and that the joint was more or less as strong as the dowels, and glue being a bonus.

 

[Jacob]

Draw boring isn't about strength it's an alternative to cramping. It is useful for nipping up the joint e.g where the shape makes clamps difficult to apply, such as stair string to newel. If you can clamp it tight a neat drilled through dowel would probably be stronger.
But in any case a wedged through tenon would be stronger stlll IMHO - no holes making weak spots, more tenon and more glued area

 

[Togalosh]

I've just read up on 17th century stool making which relies on drawerboring as no glue is used & those last for 100's of years & an old dowel took 45minutes to extract from a stool being reconditioned - but the stools are obviously not used in combat.

The book discussed axes & battle axes & they are wedged tennons but enter the axe head differently & the axe head being metal takes a lot more expansive force - they also use lag bolts but they are not pretty.

Last week I gave drawboring a go for the first time & it was easy enough but the wood selection for the dowel is all important - very straight grain only.

HTH

Togs

 

[marcros]

Draw boring isn't about strength it's an alternative to cramping. It is useful for nipping up the joint e.g where the shape makes clamps difficult to apply, such as stair string to newel. If you can clamp it tight a neat drilled through dowel would probably be stronger.
But in any case a wedged through tenon would be stronger stlll IMHO - no holes making weak spots, more tenon and more glued area

But if nipped up, in theory it is stronger than non doweled/drawbored because it cannot move anywhere. So the perma-clamping of drawboring must add some strength, even if that is not its prime purpose. I suppose that if it is clamped, then through dowelled, then it is much the same thing.

 

[nanscombe]

Looking at the Tonfa it could almost be thought of as similar to attaching a mallet / hammer head to its handle. The handgrip being the handle and the striking surface the head.

Aren't a lot of them wedged tenons?


Looking at various images in Google some seem to be a wedged tenon, like this one, and some seem to have a peg through the side of the weapon, like this one.

 

[anaminal]

For your tonfa, though, I'd worry that drawboring would also weaken the wood itself and make it more likely to split...as you need to cut two lateral holes in it parting the grain in two axes, rather than just one for a regular mortice.!

Sorry, I'm not understanding this. How does it split the grain in 2 axes?

Looking at various images in Google some seem to be a wedged tenon, like this one, and some seem to have a peg through the side of the weapon, like this one.

Yeah - I've looked at a lot, both online and those used in my class and there are a great variety of styles. My instinct was that the wedge would be stronger as it braces the tenon against the mortice laterally, rather than just pulling it in vertically.

The only way to know would be to make a series of samples and then measure the breaking force required... but that'd be time consuming and (assuming I used the same quality oak I would in the tonfa for accuracy) - expensive! I think I'll go with the forum's instincts on this one. Thanks all!

Kind Regards,
Chris

 

[Jacob]

[..... ...
The only way to know would be to make a series of samples and then measure the breaking force required... ......

Do they break? If so have a look at broken ones and see if you can spot the weakness.

 

[G S Haydon]

I think this one is mainly down to context rather than strength. A basic rule of thumb would be something like..........

Drawbore would be more common on large joints, for instance on oak framing, gates, the frames of windows and doors or Medieval type work. The pegs keep a nice pressure on the joint and it is well suited to the larger joints

Wedges are more common on joinery like caesments, sashes and doors. I like to wedge by driving the wedge into two slots cut into the tenon. The wedge is then glued inside the tenon rather than just putting pressure on the outside (just my preference though)

As with most things the edges blur as to what is best.

 

[JakeS]

For your tonfa, though, I'd worry that drawboring would also weaken the wood itself and make it more likely to split...as you need to cut two lateral holes in it parting the grain in two axes, rather than just one for a regular mortice.!

Sorry, I'm not understanding this. How does it split the grain in 2 axes?

To insert the handle via a wedged mortice-and-tenon joint, you have to cut a hole in the main shaft of the tonfa perpendicular to the main axis, right? So you're parting the grain in one axis - inserting something which, should it swell or have a lateral force applied on it, could encourage the entire shaft to split end-to-end along the grain.

To insert the handle via a drawbored M&T you would have to cut the mortice, which parts the grain in one axis, and then drill another hole perpendicular to the mortice and also perpendicular to the shaft for the drawbore dowel, which means a second something inserted between the fibres of the grain which could inadvertently cause a lateral force which may split them apart right the way down the shaft in a second axis. This could happen with expansion if the tonfa gets wet or left on a radiator, it could happen with a sharp knock.




I don't think it's a major concern, but it's something to bear in mind! In my limited experience it seems to me that wood is more likely to split parallel to growth rings than perpendicular to them, so presuming that's true, if you're only cutting the one hole you can make sure to do it perpendicular to the growth rings in the shaft and mitigate the risk of splitting. But that's more difficult to do when you're cutting two holes which are at right-angles to each other!

 

[Phil Pascoe]

You don't have to split your tenon at all - flare the mortice slightly at the back, drop a spot of glue in and stick your wedges down the outside of the tenon.

 

[Jelly]

I think this one is mainly down to context rather than strength. A basic rule of thumb would be something like..........

Drawbore would be more common on large joints, for instance on oak framing, gates, the frames of windows and doors or Medieval type work. The pegs keep a nice pressure on the joint and it is well suited to the larger joints

Wedges are more common on joinery like caesments, sashes and doors. I like to wedge by driving the wedge into two slots cut into the tenon. The wedge is then glued inside the tenon rather than just putting pressure on the outside (just my preference though)

As with most things the edges blur as to what is best.

That was my impression too, in fact I was under the impression that draw boring was originally a technique for building frames in green wood, pulling the shoulders of the tennon tight to the mortice so the shrinkage as the wood dried eventually locked the joint.

 

[Fromey]

I've found drawboring fun and really effective, but have you seen the prices of drawbore pins!

 

[Jacob]

I've found drawboring fun and really effective, but have you seen the prices of drawbore pins!

You don't need them. A long well shaped dowel will do it in one. But if there are several it's good to pull them up with a pin, or a pair of. Any old bit of iron will do, if the right diameter and tapered. They were often blacksmith forged to a taper - not filed or machined

 

[powertools]

I've found drawboring fun and really effective, but have you seen the prices of drawbore pins!

Cheap long taper punches are very effective for this.

 

[G S Haydon]

+1 to Jacob and Powertools,

The proper pins are really nice and I would not dissuade against anyone purchasing them but as has been pointed out nearly anything similar can do the job.