Through mortise and tenon wedge size

[johnfarris]

I making some softwood timber gates which have through mortise and tenons.
Having done some research I have found out the mortice is splayed to accept the wedges which will be fitted at the ends of the tenon. my tenon is 20 x 70mm

What I have not been able to work out is

How do I determine the wedge size?
How much do I splay the mortice?
At what point in the process is it best to splay the mortice as I have chopped them out straight with my morticer to my marked lines?


Thanks inadvance

John

 

[topchippyles]

Rule to thumb john is 1 in 7 so example,7 inches up and 1 inch across,Draw a line and set the bevel which will give the angle required.Depth is normally about a third of the thickness of the joint,I would also dowel through the tennon to give extra strength.

 

[johnfarris]

Rule to thumb john is 1 in 7 so example,7 inches up and 1 inch across,Draw a line and set the bevel which will give the angle required.Depth is normally about a third of the thickness of the joint,I would also dowel through the tennon to give extra strength.

Thanks for replying

When do you chop the splay part of the mortice? Also do you increase the length of the mortice to give wedges a start?

 

[custard]

I'll say at the outset that I've very little joinery experience, so I'll defer to the very experienced joiners on this site when it comes to gate construction!

However, I'm a cabinet maker and I regularly make wedged through tenons like these,

The layout scheme I generally follow is to divide the overall length of the wedged tenon into nine equal parts, it's then 1 part tenon, 1 part wedge, 5 parts tenon, 1 part wedge, 1 part tenon.

The tricky part is cutting the mortice splay to exactly accommodate the wedges, I draw it all out full size or double size and take dimensions and angles from the drawing. In the trade there's an expression for when this goes wrong, they're called "Laurel & Hardy Tenons" because there's one fat wedge and one thin wedge! To prevent this you either use a spacer as you're tapping the wedges in to ensure they go in to the same depth, or you gently tap them home with light alternate taps.

Hope that helps.

 

[johnfarris]

I'll say at the outset that I've very little joinery experience, so I'll defer to the very experienced joiners on this site when it comes to gate construction!

However, I'm a cabinet maker and I regularly make wedged through tenons like these,



The layout scheme I generally follow is to divide the overall length of the wedged tenon into nine equal parts, it's then 1 part tenon, 1 part wedge, 5 parts tenon, 1 part wedge, 1 part tenon.

The tricky part is cutting the mortice splay to exactly accommodate the wedges, I draw it all out full size or double size and take dimensions and angles from the drawing. In the trade there's an expression for when this goes wrong, they're called "Laurel & Hardy Tenons" because there's one fat wedge and one thin wedge! To prevent this you either use a spacer as you're tapping the wedges in to ensure they go in to the same depth, or you gently tap them home with light alternate taps.

Hope that helps.

Thanks custard. Every time I see you name and avatar I hear the theme tune in my head :lol:

When researching on the net for info I have come across plenty of methods detailing how you've shown but on furniture not joinery I wonder what the reason is?

www.geoffswoodwork.co.uk/mortise01.htm

On the excellent site above Geoff says the mortise should be splayed to a ratio of 1:10 but no more than 1:7 . Not sure whether to do this by hand or tilt the stile in my morticer. I am planning on making a jig for my bandsaw to make the wedges.

I am wondering why its the mortice that get splayed and not the tenon surely it would be easier to to splay the tenon.

John

 

[custard]

I am wondering why its the mortice that get splayed and not the tenon surely it would be easier to to splay the tenon.

You’re better off sacrifing some stile strength rather than sacrifing tenon strength. You’ll also gain a smidgeon more glue surface this way. But the biggest reason is that with an angled mortice the tenon can never pull out, if you trim the tenon you defeat the main purpose of wedging.

 

[johnfarris]

I am wondering why its the mortice that get splayed and not the tenon surely it would be easier to to splay the tenon.

You’re better off sacrifing some stile strength rather than sacrifing tenon strength. You’ll also gain a smidgeon more glue surface this way. But the biggest reason is that with an angled mortice the tenon can never pull out, if you trim the tenon you defeat the main purpose of wedging.

Oh I see that makes sense.

Thinking about this splayed mortise a little more. I am thinking you do not chop out the whole width of the wedge out of the mortice as you have to allow for compression of the wood fibres by the wedge?

 

[custard]

I am thinking you do not chop out the whole width of the wedge out of the mortice as you have to allow for compression of the wood fibres by the wedge?

Correct, although in reality it's actually compression of the weaker long grain of the wedge by the tougher end grain of the stile. Another thing to note (which I see you've already figured out in your sketch) is that the slope doesn't extend right through to the inside of the stile, I usually arrange for the slope to terminate about 6mm from the inside opening of the mortice.

I'll say again, I'm a furniture maker not a joiner so don't take my methods as gospel when it comes to gate construction! For one thing furniture makers almost always have the wedges set in from the edges of the tenon and use contrasting wedge timbers, both are done that way for decorative reasons. But joinery construction doesn't faff around with any of that, same timbers and the wedges on the outside of the tenons.

 

[johnfarris]

I am thinking you do not chop out the whole width of the wedge out of the mortice as you have to allow for compression of the wood fibres by the wedge?

Correct, although in reality it's actually compression of the weaker long grain of the wedge by the tougher end grain of the stile. Another thing to note (which I see you've already figured out in your sketch) is that the slope doesn't extend right through to the inside of the stile, I usually arrange for the slope to terminate about 6mm from the inside opening of the mortice.

I'll say again, I'm a furniture maker not a joiner so don't take my methods as gospel when it comes to gate construction! For one thing furniture makers almost always have the wedges set in from the edges of the tenon and use contrasting wedge timbers, both are done that way for decorative reasons. But joinery construction doesn't faff around with any of that, same timbers and the wedges on the outside of the tenons.

Point noted about being a furniture maker and thanks for the helping anyway

 

[HOJ]

Don't make the wedges over long as they are likely to snap off if you miss hit them when you drive them home, and put plenty of glue in, will help seal the end grain on the stiles.

From you drawing, I dont see the need for the haunch as you are not on an outside face edge, I would probably consider a draw bore dowel in there as well, depending on how wide the gate is.

 

[Racers]

I cut the tapers in the mortice with a chisel and put the wedges in like Custards picture to lock the rails in place.

And don't forget a diagonal brace pointing towards the bottom hinge.

Pete

 

[space.dandy]

I am wondering why its the mortice that get splayed and not the tenon surely it would be easier to to splay the tenon.

You’re better off sacrifing some stile strength rather than sacrifing tenon strength. You’ll also gain a smidgeon more glue surface this way. But the biggest reason is that with an angled mortice the tenon can never pull out, if you trim the tenon you defeat the main purpose of wedging.

Ok, now I’m confused. The sketch shows the wedges on the outside of the tenon. Doesn’t this also defeat the main purpose of wedging, in exactly the same way as angling the tenon in a straight mortice? I thought the whole point was that the wedge forced the tenon apart to conform to the angle of the mortice?

 

[custard]

Ok, now I’m confused. The sketch shows the wedges on the outside of the tenon. Doesn’t this also defeat the main purpose of wedging, in exactly the same way as angling the tenon in a straight mortice? I thought the whole point was that the wedge forced the tenon apart to conform to the angle of the mortice?

I'm second guessing the logic of the joiners here, but if I was aiming for functionality rather than appearance then I'd do my wedges in exactly that fashion.

Here's why. There's little cramping pressure in mortice and tenon work, you're basically relying on the friction fit between the tenon cheeks and the mortice wall to deliver pressure. It generally works out okay because the glue surface is so very large, rather than the glue strength per square centimetre is particularly high. But when you pound in those wedges on the outside of the tenons then there's a lot of pressure between the wedge and the tenon. Which in turn means a very good glue bond.

Consequently even if the mortice to tenon glue bond fails it's unlikely that the wedge to tenon bond will ever let go.

 

[space.dandy]

Ok, now I’m confused. The sketch shows the wedges on the outside of the tenon. Doesn’t this also defeat the main purpose of wedging, in exactly the same way as angling the tenon in a straight mortice? I thought the whole point was that the wedge forced the tenon apart to conform to the angle of the mortice?

I'm second guessing the logic of the joiners here, but if I was aiming for functionality rather than appearance then I'd do my wedges in exactly that fashion.

Here's why. There's little cramping pressure in mortice and tenon work, you're basically relying on the friction fit between the tenon cheeks and the mortice wall to deliver pressure. It generally works out okay because the glue surface is so very large, rather than the glue strength per square centimetre is particularly high. But when you pound in those wedges on the outside of the tenons then there's a lot of pressure between the wedge and the tenon. Which in turn means a very good glue bond.

Consequently even if the mortice to tenon glue bond fails it's unlikely that the wedge to tenon bond will ever let go.

Ok, I can understand that. But wedging into the tenon, not only do you have cramping and glue but you also have geometry itself on your side, which is surely the best result. Unless it’s just seen as overkill.

 

[Bradshaw Joinery]

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