Wedged through M&Ts

[ByronBlack]

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

 

[woodbloke]

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]

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]

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]

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]

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]

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]

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]

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]

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