Thread: Rebate joint failure - what is a better solution?

Maybe not enough giue.

I put heaps of glue in and had squeeze out in several spots.

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That is essentially a butt joint of end grain to side grain. End grain is poor with glue. I suspect that the outside sections moved, and this broke the glue line.

Far better would have been a sliding dovetail joint, which would trap the sides.

A fix now requires scraping out all the glue (unless you used hide glue, which accepts fresh hide glue over it. All others do not). Then reglue and use nails angled from the inside to prevent it lifting out of the dado/housing (it is not a rebate).

Regards from Perth

Derek

A good fix will be to glue a strip of timber in the housing, let the glue dry and then flush that strip down to the surface of the top/bottom panels. Then make a sliding dovetail. It will involve cutting the female dovetail in the top/bottom panels, and reforming the male dovetail on the current square tongue. It will be a fair amount of work, but if you have mad skillz with a router, it can be fairly straight forward.

It looks to me that the may have also been some differential movement between the top / bottom and the verticals. Including some cupping of the top.



as suggested by Kuffy, the fix will involve re-making the joint.

to avoid the risk of missing too much glue when scraping the cured stuff off, I'd narrow the tongue by about 1/2 mm on each face and widen and deepen the slot by a similar amount.
I'd then glue strips to the tongue -- being sure to align long grain to long grain -- to take it back to slightly wider than the finished width of the uprights.

I'm assuming you want to use stopped dados?
In which case the sliding dovetail will need to employ "fingers".
Cut both parts of the joint as though it were all one piece, then make the "fingers" by removing every second 25 mm (or so).
The corresponding packets in the top / bottom just need to have the shoulder of the slot removed.

best wishes

glue may also have been off as titebond has limited shelf life if it's gone thick and gluggy its strength has reduced and it's on it's way out if it's separated in the bottle it's finished.

Thanks for the tips Ian. I didnt want the slot seen fron the ends so yes the joint was a "stopped dado".

You are right that the top has cupped slightly. Maybe the 2 week gap between making the top and assembling the table was too long... I can flex the cupping straight so if I remake the joint using dovetail fingers it will probably pull it straight. Would you reflatten the top before assemling it again?

Mike

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One thing that might be an option, would be to clean the glue. Use a kreg jig or pocket hole to pull it down and fasten. Then dowel up the pocket hole to hide it?

Just a thought.

I was pondering pocket holes as a possible solution, but wasn't sure about their strength screwing into end grain (albeit at a slight angle).

Mike

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Originally Posted by Stanger

I was pondering pocket holes as a possible solution, but wasn't sure about their strength screwing into end grain (albeit at a slight angle).

Mike

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Pocket hole screws would be strong enough to hold it down but you'll have to close the gap with clamps first. The screws alone aren't strong enough to pull the top down on its own.

Hi Mike

Originally Posted by Stanger

You are right that the top has cupped slightly. Maybe the 2 week gap between making the top and assembling the table was too long...

that, I think, is the core problem.
I doubt if the time between making the top and assembling the table is a significant issue.

I can flex the cupping straight so if I remake the joint using dovetail fingers it will probably pull it straight. Would you reflatten the top before assembling it again?

A bit difficult to tell, but I think the way the boards are arranged in the top makes it prone to cupping.

Is the cupping on one side only?

Re-flattening should take out the current cup, but may not be a permanent fix, as the top just may want to move.

I don't like using pocked screws in furniture, but then may work if driven from the verticals into the top.

If you do decide on dovetail fingers, make sure that the end finger (not a gap) is located on the cupped side.

I thought I'd give a quick update: after browsing the forums and ponering the helpful responses above I thought I would start with the simplest solution first and if that didn't work then try something a bit more serious. I put the now detached top on the grass in the sun. I had the cupped side down (bowed out side facing sun) and checked it every now and then to see if the cupping was removed. To my surprise after an hour and a half the top was flat again! I took it inside to let it cool down and a few hours later it is still flat.

I'm now very tempted to have another go at glueing up the stopped dado joint now. I've removed the old glue and a little timber so the joint is not as tight as it was previously. I'm thinking of gluing with plenty of glue and leaving the clamps on for 24 hrs...

Mike

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If the joint is no longer tight then PVA glue will be useless; you will need a gap filling glue like epoxy. Polyurethane glue might work; Elanjacobs I think would be the best person to ask as he is a professional cabinet maker with a lot of experience with poly.

If you go with the epoxy idea then you can put a very slight dovetail profile on both the dado and the tongue, once the epoxy has set hard it will never pull out.

Mike, I would recommend skew nailing as well, since I suspect that the panel is liable to move again (looking at the end grain - it seems vulnerable to cupping). The nails should be driven under the surface so that they do not show. Use a nail punch to do this.

Regards from Perth

Derek