help needed with a tricky joint

[Walney Col]

Hi.

I'm in the process of making a pagoda-style shadow box and I'm having a spot of bother envisaging a good way or jointing the roof beams. This is the basic idea...

Where the 4 beams all meet in a compound mitre joint...

The trouble is that I'm not a joiner by any stretch of the imagination but I know enough to know that end grain joints are unlikely to last long.
So I thought how about a kind of half lap joint instead...

Which looks a but too funky for me (not to mention difficult to achieve) but even that's end grain to side grain and not likely to last much longer than the compound mitre joint.

So how would you keep this general idea but make the joint strong enough to withstand regular handling? The box has a light in it BTW and lifting the roof off is the only way to access it so the whole thing has to be easily removed. I thought about milling a slot across the top and inserting a stitch but then realised that the second stitch would immediately cut the first one clean in half.

*scratches head*

 

[rdesign]

have a transition cube that can be shaped in the centre. Then mortices the 4 sides for small tennons from the beams, the shoulder joint should remain good and tight even with minor wood movement.

but on such a thinking small piece 45 food joints should work. just work out ur angle.

another solution is make 2 roof members and have a half lap joint.

regards Richard

 

[custard]

Nice Sketch Up work!

 

[Walney Col]

have a transition cube that can be shaped in the centre. Then mortices the 4 sides for small tennons from the beams, the shoulder joint should remain good and tight even with minor wood movement.

but on such a thinking small piece 45 food joints should work. just work out ur angle.

another solution is make 2 roof members and have a half lap joint.

regards Richard

Thanks Richard.
I'm not sure what you mean by food joints but I think I may resort to trying tenons.

Col.

 

[Walney Col]

Nice Sketch Up work!

Thanks custard.

 

[rdesign]

auto correct doh sorry should proof read more was just heading out... roof joints it was suppose to be like a hip rafter joint as shown in your sketch up it will just be the miters might spread a little at the base with expansion but if the parts are small isn they movement will be hardly noticeable.

hope to see the picks of how it turns out and the method u choose.

 

[Guggs]

It's probably easier than you think .
I would attack it like this .
Make some test pieces and replicate the cube to .
That way you have a 3 dimensional view how the pieces match at the top .
Being a radius curve you can make the pieces longer than required as you can move the piece along and start again with the joint .
Great little project !

 

[Walney Col]

Thanks for the input lads.
I don't know how successful I'll be but I'm going to have a go at this one which out to be plenty strong enough;

 

[AndyT]

Good luck with this!

It's not something I've ever built, but applying techniques used in chairmaking, it could help if you start with relatively large pieces of wood, of ordinary rectangular cross section. Cut the joints first, and only when you have got them fitting properly, mark and cut the curves.

Without some straight lines you won't have a reference surface to measure or cut any of the joint surfaces.

 

[Jacob]

IMHO those fiddly M&Ts would fail due to too much cross grain
I'd either
do plain butted joints with dowels, reinforced with a metal plate below
or have a central block (square or turned round) with M&Ts - this still wouldn't be very strong so would probably still need a bit of metal back up.

 

[Phil Pascoe]

Central post, or half lap one way, cross halving the other?

 

[Walney Col]

After a bit of faffing around this is my final joint design...

I've rough cut the parts on the band saw but still have to sand to the finished size and fit & glue the joint itself.
The tapered part are 3mm thick and 12mm long and even without glue there's a fair bit of wedging going on so I'm reasonably happy it's not likely to fall apart but if needs must a glued in vertical dowel should hold it.

 

[Walney Col]

Someone asked for photos of the finished joint...

I'm waiting for the glue to cure than I'll sand the very top of the joint to blend it in with the side pieces. I'm quite pleased with how it's turning out and with 3 times the glue area of a half lap I don't think there's any doubt that it'll be strong enough. The wood is oak in case anyone's wondering.