haunched mortise and tenon

[johnfarris]

Hello people

I have seared the forum & had no luck trying to find the following information
When setting out a haunched mortise and tenon, what calculation do you use to work out the length of your haunch?
I know the width & thickness is a third

Any help much appreciated

j

 

[Dodge]

If you are cutting a square haunch to fill a groove or traditional sloping haunch then I tend to still work on thirds as with the width of the tenon.

So if the overall width of the tenon is 30mm I would make the haunch 10mm and the tenon 20mm wide accordingly. There is no hard and fast rule here its what works for you and makes a strong joint.

Just make sure that you don't get the mortice hole too near the edge of the stile to prevent break out occuring

HTH

Rog

 

[Jacob]

rule of a third is only rough guidance. The thickness is usually down to whatever size mortice chisel you have. So in stuff that's from 1½ to 2" finished you'd find a ½" M&T but it might go up to 5/8" at 2" e.g. if it was a big heavy door. Width depends on other details such as where it is and width of the rail etc. so a third doesn't come into it.
Haunch goes from the tenon to the edge of the rail, so there's nothing to calculate.

 

[Dodge]

Jacob, I think you may have misread what was actually being asked

The query related to the haunch, whether tapered or square and how long the haunch should be

 

[Jacob]

Jacob, I think you may have misread what was actually being asked

The query related to the haunch, whether tapered or square and how long the haunch should be

Oh right. Er - square; 1/2" tenon would have 1/2" of haunch - extending from tenon to the full width of rail but could be tapered off to zero and be out of sight.

 

[Dodge]

:roll: ](*,)

 

[Jacob]

:roll: ](*,)

So what have I misunderstood this time? :roll:

This one shows what I mean though the haunch looks slightly less than square in section as viewed from above.

PS just shows how confusing things can get - the image shows a rebate on the rail but not on the stile. Not my drawing - just lifted it from the net. Here's a few more.

 

[johnfarris]

Thanks for replying

This is the size i am after

 

[Melinda_dd]

I agree with Dodge, I would go for a third as well, a third of the length of the tennon .... that's what I've been taught at college recently anyway!

 

[Jacob]

I'd stick with square i.e. the length same as width. It's a sort of standard, but with variations according to other details such as rebates and slots. If there's slot then the haunch fits in the slot. If there's a rebate the haunch goes past the rebate to about equal to it's width.
A length of a third is too long IMHO and as a rule of thumb "square" would be better.

The purpose of the haunch is to close the gap and also to prevent "lipping" - where the rail twists slightly against the stile and the joint goes out of alignment. To do this you only need a short stub of a haunch.

 

[SBJ]

I'd stick with square i.e. the length same as width. It's a sort of standard, but with variations according to other details such as rebates and slots. If there's slot then the haunch fits in the slot. If there's a rebate the haunch goes past the rebate to about equal to it's width.
A length of a third is too long IMHO and as a rule of thumb "square" would be better.

The purpose of the haunch is to close the gap and also to prevent "lipping" - where the rail twists slightly against the stile and the joint goes out of alignment. To do this you only need a short stub of a haunch.

I'd agree with most of this. It largely depends on what you are making and whether there are rebates or grooves. I suspect that on smaller components (furniture?) the ratios will be different to those on larger components (architectural joinery)-

If you can give more specific info on what you are making, then you will get more specific advice.