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Best joint for 3 way joint

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Spoonboy

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Hi all. Looking for expert advice on the best joint for 100mm timber for porch frame. Thanks in advance
 

custard

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Take my advice with a pinch of salt because I'm a cabinet maker rather than a joiner, but when it comes to a three way joint there are two obvious options.

First is a three way mitre joint, the joint that you sometimes see at the corners of wooden framed, glass display cabinets. It's also popular for furniture, in particular side tables and desks. If you're equipped to cut a flawless mitre (and it really does have to be flawless) then this isn't a difficult joint, you just cut sequential mitres and then it's reinforced with loose tenons or splines which drop into mortices that you cut on a router table. There's no reason why it couldn't be scaled up to 100mm square timbers. The only question I'd have is the long term weather resistance of loose tenons?

And the other option is a straightforward pair of mortice and tenons at each corner. Just think for example of a sturdy table, where the two apron rails joint into the leg, so effectively a three way joint. You could always then peg the tenons for added security and less reliance on the glue bond.
 

MikeG.

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The normal thing, Custard, is to design the joint out. You don't find 3 bits of wood meeting at their ends at a corner in traditional framing. At a porch, the post would generally meet the wall plate (which overhangs slightly) with a M&T, and the tie (across the front of the porch) is raised using a half-lap, or dovetailed half lap. The rafters then sit on the tie if you are being really traditional.
 

custard

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You don't find 3 bits of wood meeting at their ends at a corner in traditional framing.
I take your point. Interestingly I seem to recall some Chinese furniture that was built much the same way.
 

MikeG.

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He's been given the correct answer. This has to hold up the roof. Any variation on a 3 way mortise and tenon ends up with the entire weight of the roof taken on just the tenon.
 
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TomB

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The normal thing, Custard, is to design the joint out. You don't find 3 bits of wood meeting at their ends at a corner in traditional framing. At a porch, the post would generally meet the wall plate (which overhangs slightly) with a M&T, and the tie (across the front of the porch) is raised using a half-lap, or dovetailed half lap. The rafters then sit on the tie if you are being really traditional.
Mike,
How is the rafter attached to the tie? I can’t tell from the photograph.
Thanks,
Tom
@MikeG.
 
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