I’m not a master woodworker, and I’ve only made tenons a few times. But the discussion about glue squeeze-out on the last podcast reminded me of an unexpected problem I ran into last time I made tenons.
These were big tenons – about 8x8x3 cm
I cut the mortises with a drill press and a chisel. Given my lack of experience – the mortises were definitely did not have completely flat sides. A couple of the tenons were obviously loose. I dry fitted everything and it looked good enough.
But then I put glue on them (mortises and tenons, on each side). What happened was that the glue formed a tight air seal around the mortise, and pushing the tenon felt exactly like a bicycle pump that’s not connected to the tube properly. I’d push, it would push back. I’d push harder, it would push back harder.
I think I ended up solving the problem with a sledgehammer. Seriously, that’s how much force it needed.
I can’t be the only one who ran into this. But how come I’ve never heard it mentioned by anyone? I just finished reading Timothy Rousseau’s article where he also goes over gluing tenons, but the pump problem is not mentioned at all.
Is it perhaps that on smaller tenons there’s so little air displaced by the tenon that this doesn’t happen? Or it that noone’s tenons actually fit it as well as they advertise, and instead leave some gaps for air to escape?
Replies
First, always make your mortises slightly over depth (maybe 1/8" or so) to allow some space for extra glue to collect. Second, you can cut some small grooves in the tenons to allow air to escape. Third, I have always found that clamp pressure is more effective in seating the joint rather than beating on it.
I shave off one corner of a tenon side with a chisel so the air can come out. As if I ever make a perfect-fitting one.
Good suggestion. My tenons rarely fit tightly along the edges anyway.
To the OP, you may have also used far more glue than you needed. Try using a small brush (the cheap throw-a-way acid brushes work well) and just paint glue on the tenon cheeks and mortise walls. That is all that is needed.
I'm in the camp of "too much glue is better than too little glue" :)
Thanks for the suggestion to shave off a corner, that sounds like a simple and efficient and invisible solution!
Too much glue however, is NOT better than the right amount of glue. Bilyo's suggestion of using a brush to paint glue on the tenon is the way to go. Too much glue resulting in blobs of squeeze-out does nothing to enhance the strength of the joint. It's a waste of glue, consumes more of your time in a messy clean up, and can affect the quality of the finish near the joint.
Yeah, I agree. I do use a brush to put on just enough glue that it doesn't get tacky before I put the parts together. I suspect that's still a lot more than some people use.
Chamfer the corners. Use clamps not a hammer.
Don’t squirt a random amount of glue in the mortise. In fact a well fitting joint only need glue on the tenons.
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I agree, but you should only glue the mortise and not the tenons. As mentioned above, if you leave a 1/8 pocket at the bottom of your mortise for extra/too much glue, as you push the tenon in you squeeze the glue into the pocket. If you put too much glue on the tenon you will definitely get squeeze out as you slide/touch the tenon through the mortise.
I use cheap acid brushes to paint glue on the long grain surfaces of both
the mortise and tenon. Then, following the trick of Bob van Dyke somewhere in FWW, I insert the tenon about 2/3 of the way and then use a clean brush to wipe out the glue that has emerged in the gap. I then clamp the joint home; there is often little or no squeeze out.
Good practices. Always apply glue to both sides of the joint.
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