Reinforcing a joint

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Alpha-Dave

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Hi all, I am making a toy dog kennel for my nephew’s cuddly toy. This will be about 35 cm long by 30 cm wide.

The roof needs to open on one side. It needs to have 270 degees of swing from closed to fully open. I have looked at the standard hinges available from my local suppliers, and while cranked hinges look the best, they are definitely a finger trap hazard, therefore I am making the whole roof as the hinge, using 3/4” dowel, 1/4” brass rod and 9 mm ply.

My intention is to cut a 3/8” radius groove on the ply, and then glue section of the dowel with holes drilled in the centre to alternate sides. On my first test piece, using super glue this has been ok for the wider spaced pieces, but it would be nice to reinforce it. Obviously I can’t go through the middle of the rod where the brass rod is.

I’m thinking either: pin nails, shot at a slight angle from the dowel into the ply; or splines cut about 5 mm into the dowel and ply, probably one or two per dowel section.

Does anyone have any other suggestions for reinforcement for the dowel/ply join? Thanks in advance.

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Cabinetman

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Nice little problem, I thought at first that you had put a curved cut into the edge of the ply which I think would work perfectly well with ordinary PVA then I noticed that it wasn’t quite such a perfect curve. I think if you were to cut the ply so that it was stepped instead of curved, and then cut some matching steps along the dowel that would give you enough close fitting glueing area to work. Fiddly but doable, you may need to temporarily fasten the dowel to a piece of wood if you are going to safely pass it across your saw to put the grooves in. Ian
(But that’s where we came in ha ha)
 

Alpha-Dave

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Thanks Ian, the curves cut into the plywood are actually quite smooth, and fit the dowel nicely (made with a 6mm ball nose bit on a CNC router), the steps are mostly an optical artefact where the superglue has wicked slightly more or less into the different ply orientations.

I have to admit that these joins do appear to be reasonably strong: for each cm of join width, I am getting about 1.4 cm2 of glue area, which is side-grain on the dowel, and 50/50 side and end grain on the ply. The steps idea is interesting: If I cut steps into the ply and dowel, the the surface are would be about 1.8 cm of glue
 

Cabinetman

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Ok well that’s good, as it’s a good fit I should just stick with the curve, cramp it nice and tight and I’m sure it won’t move.
Perhaps glue the whole thing up as one, I think you may find it easier to squeeze it nice and tight that way,it would also ensure the spacing was right, and discs of cellophane between the knuckles to stop it sticking and to give it a little bit of movement later. Ian
 
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