Securing m and t joint?

[Fat ferret]

I always use glue but don't use all the way through dowels for exterior stuff and because I struggle to get decent dowel. I have used wedges both either side of the tenon and in the middle but again making wedges is a bit off a faff.

Whenever I have tried drawboring in green oak for instance it can be difficult to judge the offset and can result in me splitting the joint.

So mostly I just stick a star dowel through the joint for insurance and cause it's quickest. Probably just glue is enough anyway it's not going to fail in a door say providing it's exterior grade is it?

What does the everyone else do?

 

[custard]

PVA glue is enough if, and only if, it's really really good joint. The difference between an over tight M&T and an over loose M&T is no more than two or three passes with a shoulder plane, considerably less than a tenth of mill. The way you've been using wedges is just plain wrong.

If you're not confident of jointing every joint in a door to that accuracy you should use Cascamite or Epoxy because they have some gap filling properties (as well as providing gold standard weather resistance). Personally I'd use Cascamite because it's far cheaper and you can clean up the squeeze out with hot water.

Good luck!

 

[Lord Kitchener]

Note you are making stuff in green oak, what sort of stuff, are we talking 8" x 8" posts for an oak-framed house, or something smaller? 19mm oak dowels are customary in oak framed building work.

 

[Fat ferret]

PVA glue is enough if, and only if, it's really really good joint. The difference between an over tight M&T and an over loose M&T is no more than two or three passes with a shoulder plane, considerably less than a tenth of mill. The way you've been using wedges is just plain wrong.

If you're not confident of jointing every joint in a door to that accuracy you should use Cascamite or Epoxy because they have some gap filling properties (as well as providing gold standard weather resistance). Personally I'd use Cascamite because it's far cheaper and you can clean up the squeeze out with hot water.

Good luck!

Custard, what am I doing wrong re wedged m and t joints? I was talking about through m and t joints. I have put wedges into saw cuts in the tenon or put wedges at either end of the tenon, think the latter is called fox wedging maybe someone will enlighten me shortly.

Both well established methods I've seen in textbooks and such. I just find making wedges a bit of a faff is all.

Lord Kitchener just using the green oak as an example as I was my one and only attempt at drawboring. Most of the joints in the gates I was making went together fine but a few split and I felt I would have been as easy just putting the joint together and then drilling through and banging the dowels in after. Live and learn and the project went together fine.

Anyway was interested in how members secured their m and t's or wether glue was enough without needing a mechanical fixing, dowels wedges or what have you.

 

[custard]

[/quote]

Custard, what am I doing wrong re wedged m and t joints? [/quote]

Maybe I misread it, when you said wedges "either side of the tenon" I read that as being against the cheeks of the tenon, which if you hammered them in could split the mortice wide open! Upon reflection maybe you mean at either end of the tenon, so the wedge runs at 90 degrees to the grain?

 

[Steve Maskery]

Neither of the ways you describe is fox wedging.

Fox is very crafty.

It is a one-shot shot. They can be used in a blind tenon, and it is the bottom of the mortice that forces the wedges into the tenon. But if you get it wrong, you cannot take it apart to fettle it.

I've never done it, I've only ever seen it illustrated in books and can see no good reason for doing it. It's far too risky for me.

 

[Fat ferret]

Hi Steve, did that once at college just to see if I could. It worked but as you say it's not worth the effort.

Custard wedges would not split the grain the way I meant.

 

[deema]

Fox wedging is exciting! Done it a few times in doors where I didn't want the tennon to show through on lock side of the door. The Mortice needs to have be angled at either end so that the pocket is wider at the bottom than where the tennon enters. The increased width needs to be slightly less than the width of the edges being inserted. This allows the tennon to spread and allow the wedges to be driven home successfully.

I found the best way to gain confidence that I had the geometry right and created a secure joint was to use scrap to trial and error the joint, and then rip it open to see how the joint appeared after I'd tested it for security. I used glue to ensure a proper simulation. If the chamfer in the Mortice is too wide, the joint is not secure and wobbles, if it's not enough you can't pound the joint home. It really depends on the wood species for the amount of compression that can be created.

 

[Sgian Dubh]

The fox wedged M&T is essentially as below. It has its uses, but can be a bit tricky to execute successfully. I recall an occasion where a fairly thick overhanging solid wood panel top needed to be fixed to cabinet sides, and the top had cupped significantly, where perhaps other joinery wouldn't have sufficed to hold the top flat. The sides could have been attached to the top with through wedged M&Ts, but would have been undesirably visible. The fox wedged M&T was the solution, three per side to top connection: it worked a treat. Slainte.

 

[Sgian Dubh]

What does the everyone else do?

There isn't one configuration of M&T that's appropriate for all purposes, and each situation needs a configuration to suit the end use.

If you're splitting the wood when driving in the dowel or trunnel something is not set out right, probably the offset of the hole bored through the tenon, or perhaps even the size of the dowel. Exterior woodwork made out of green or partially dried wood nearly always benefits from mechanical locking to supplement any adhesive used, so I think you probably need to look at potential causes of the splitting, establish what it is, and adjust the set out or dowel size used. Trunnels are frequently roughly square in section and tapered in the length, not round, and the sharp corners bite usefully into the wood when driven into a tighter round hole. Slainte.

 

[Fat ferret]

Probably just me being a bit out with drill. It was no big deal and the project turned out fine just seemed more trouble than it was worth drawboring to get a tight joint, the joint was already tight!

 

[Paddy Roxburgh]

PVA glue is enough if, and only if, it's really really good joint. The difference between an over tight M&T and an over loose M&T is no more than two or three passes with a shoulder plane, considerably less than a tenth of mill. The way you've been using wedges is just plain wrong.

If you're not confident of jointing every joint in a door to that accuracy you should use Cascamite or Epoxy because they have some gap filling properties (as well as providing gold standard weather resistance). Personally I'd use Cascamite because it's far cheaper and you can clean up the squeeze out with hot water.

Good luck!

Custard, I have always believed what you've written above to be true. However I recently read an article by Mathias Wandel where he found a 0.3mm gap to give a stronger joint using yellow glue, which is essentially pva http://woodgears.ca/joint_strength/glue_methods.html


Fat Ferret, whst do you find to be a faff with the wedges? Are you doing them by machine? I just mark them on a piece of wood and cut them with a fine saw (I use a jap saw but a fine toothed dovetail saw would do the same thing). No faf at all, and believe me I know how to faff. The biggest hassle of wedged tenons is cutting the dovetailed mortice
Paddy

 

[Fat ferret]

No machine. By hand when I bother, which is seldom. It's just one extra thing to do and customers don't know the difference anyway although the wedges can look lovely on something that's not getting painted.

 

[Sgian Dubh]

Probably just me being a bit out with drill. It was no big deal and the project turned out fine just seemed more trouble than it was worth drawboring to get a tight joint, the joint was already tight!

Draw boring has a very useful role in green or partially air dried woodworking, especially on large frameworks, but in smaller constructions too, such as garden furniture. In most cases there will be appreciable wood movement (usually primarily shrinkage in the first instance, but also expansion over seasons) after the project is assembled and in service. The draw bored dowels or trunnels help through pulling the joints up tight, mechanical locking, compensate for likely longer term glue failure, and shrinkage of the morticed part (as both parts dry) shoulder line away from the shoulder line of the tenoned part. Slainte.

 

[custard]

I recently read an article by Mathias Wandel where he found a 0.3mm gap to give a stronger joint using yellow glue, which is essentially pva http://woodgears.ca/joint_strength/glue_methods.html

Thanks for posting that, it is an interesting article. However, the author himself says he's confused by the findings and I can understand why! In a nutshell, I'm just not buying it. Gappy joints are bad joints, and with PVA they're weak joints too.

The most authoritative account I've come across on gluing is by Bruce Hoadley, and I think I'll continue to be guided by his advice,

1. Optimum gluing pressure for temperate zone hardwoods is in the range 100-250psi, dense tropical hardwoods may require up to 300 psi. Which basically means outside of an industrial workshop we'll always be well below optimum clamping pressure, for example the 14 psi that I rely on for vacuum pressing is just barely making it into the lowest acceptable category. Given that we're inevitably going to be so far below optimum clamping pressures we need to do everything else that Bruce Hoadley advises as well as we possibly can in order to stand a chance of achieving decent joints.

2. The wood should be smooth, flat, and freshly worked. Glue surfaces should mate as perfectly as possible.

3. Glue should be spread in a thin film on both mating surfaces to ensure adequate wetting.

4. Use clamping cauls to evenly distribute the puny amount of pressure we are able to generate.

5. Keep your clamps in good condition, Hoadley points out that a rusty clamp will only deliver half the pressure of a clean, oiled clamp.

 

[Paddy Roxburgh]

Custard, to be honest I completely agree with you and always try to make make my joints as accurately as possible, a good joint in my opinion should need to be knocked in with a mallet but only with light taps, edge joins should be square and straight enough to see no light through.
just for interest check out this article by the same guy, he repeated his tests also using polyurethane (gorilla glue). http://woodgears.ca/joint_strength/gorilla_glue.html . This time the pva still came out stronger with a gap but the poly was useless. I sometimes hear a guy at work saying how great poly is for filling gaps (and believe me his work has some gaps to fill!!), I've always thought it was nonsense, nice to see some empirical evidence.
Paddy