How to glue mortise and tenon - Woodworking Talk - Woodworkers Forum
 
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post #1 of 13 Old 01-23-2013, 02:42 PM Thread Starter
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How to glue mortise and tenon

My first project with mortise and tenon went less than as well as I wanted it to. It is a headboard for a bed. My dry fit was nice and I was satisfied with the way it looked. It was snug, maybe more than it should have been considering how glue up went.

I coated the tenons with glue. I just drizzled it on and spread it with my finger. Then proceeded to put the parts together. They barely fit then, and left a slight gap where the tenon shoulders met the mortised wood. Did I use too much glue, or have them slightly too tight when dry fitted?

Before I did the final assembly, I had it all dry fitted and left that way for several days. Then knocked it apart to glue it up yesterday. In doing so, one of my really long tenons (more like a long tongue in groove joint really) split coming out of its mortise (slot). So, I glued it up as a repair and clamped it, left it overnight, and didn't reassemble everything until today. That's when things barely fit. I don't know if it was too tight a fit, too much glue, or 24 hours left sitting apart. Moisture content in my shop has not changed and the wood is dry to less than 6%, and was so when milled. These are 4" wide by 1/2" thick tenons on pine 2x6 wood going into mortised Doug fir 4x4's. I had to put the parts together using a rubber mallet, even during dry fit.

I hope I gave enough info for someone to help me understand how it might have went better (and yes, I know using construction grade lumber wasn't the best, for the future).

Last edited by Duane Bledsoe; 01-23-2013 at 02:50 PM.
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post #2 of 13 Old 01-23-2013, 03:33 PM
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You may have made the tenons too long.

George
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post #3 of 13 Old 01-23-2013, 03:36 PM
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Your clues were in the phrase
"Before I did the final assembly, I had it all dry fitted and left that way for several days. Then knocked it apart to glue it up yesterday. "

Not a problem to leave for several days, but my experience is that if I have to knock an item apart, it will need force to fit it back together with the glue.

I expect you are using a yellow glue, I happen to use Titebond III, but all yellow glues are water based.

When you apply the glue, some water is absorbed, which means the wood slightly expands. It is was a force fit when "dry" it will be a more-force fit with glue.

In addition if there were glue filling the space under the tenon and if the tenon is such a tight fit the glue cannot squeeze out, the liquid will not allow the tenon to get to the bottom, since liquids do not really compress. As the glue sets, the water is absorbed and they may eventually be a gap, if you were to break into the joint and look.

If you ever look at wood dowels, they have spiral grooves down the side, specifically to allow the glue to squeeze out.

I have had the same experience as you. These days I will tweak/plane/sand so that I have a smooth dry fit by hand without a lot of force. If I am not able to disassemble by hand I tweak some more.

If I use dowels, I make the holes a bit deeper to allow for some glue. I once had a joint which fitted dry, but when I glued, I could not force the joint closed. I had to dis-assemble, make space for the glue and try again.
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post #4 of 13 Old 01-23-2013, 03:42 PM
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What I like to do when I make my tenons (witch is very seldom) I like to chamfer the tenons to give glue somewhere to go.

When it's rustic......it's rustic
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post #5 of 13 Old 01-23-2013, 09:40 PM
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Dave Paine said all and as I was reading your original post, I was thinking along the same line. Your joints are too tight. I agree with everything Dave said and will add one more little piece of advise because some one else who posted on mortise and tenon stated he was told to make the tenon 1st and fit the mortise to it. That is backwards. Cut your mortise 1st and then your tenon even a tad fat. Then you shave them down to size. A mt joint will need a bit of muscle to dry fit, should hold as a joint when moved, and separated by hand, not a hammer.

Its' never hot or cold in New Hampshire... its' always seasonal.
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post #6 of 13 Old 01-23-2013, 09:54 PM
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good info, i recently made my first mortise and tenon joints, and this answers some of the questions that crossed my mind as i was working on them.
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post #7 of 13 Old 01-23-2013, 11:55 PM Thread Starter
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Quote:
Originally Posted by BernieL View Post
Dave Paine said all and as I was reading your original post, I was thinking along the same line. Your joints are too tight. I agree with everything Dave said and will add one more little piece of advise because some one else who posted on mortise and tenon stated he was told to make the tenon 1st and fit the mortise to it. That is backwards. Cut your mortise 1st and then your tenon even a tad fat. Then you shave them down to size. A mt joint will need a bit of muscle to dry fit, should hold as a joint when moved, and separated by hand, not a hammer.
That someone else who was told to do tenons first was me. Haha. It was in another thread where I repeated it to someone else again, and then was corrected.

So my joints need to go together dry with just muscle only. I didn't have that. I had to use a rubber mallet. That was one mistake.

Someone here said my tenons were too long. Is the mortise supposed to be slightly deeper than the tenon? Mine were exactly the same. I can see it might need some extra room for the glue at the bottom.

Which brings me to my next question. How do you apply the glue? Thinly or liberally, and on all sides and the end of the tenon, or in the mortise?
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post #8 of 13 Old 01-24-2013, 02:11 AM
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Originally Posted by Duane Bledsoe View Post
How do you apply the glue?
Thin film of glue on the sides of the tennon, not the end and also all 4 sides of the mortise, not the bottom. You always want to leave the tennon just short of the mortise depth, so it won't bottom out.
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post #9 of 13 Old 01-24-2013, 02:23 AM
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unless it's a through tenon i guess, in which case a tad proud so it can be trimmed flush?
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post #10 of 13 Old 01-24-2013, 09:09 AM Thread Starter
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Originally Posted by d_slat View Post
Thin film of glue on the sides of the tennon, not the end and also all 4 sides of the mortise, not the bottom. You always want to leave the tennon just short of the mortise depth, so it won't bottom out.
How do you apply glue to the sides of the mortise if its too thin to get into? Mine might have been reached with a small brush but it was only 1/2 inch wide.
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post #11 of 13 Old 01-24-2013, 10:58 AM
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Originally Posted by Duane Bledsoe View Post
How do you apply glue to the sides of the mortise if its too thin to get into? Mine might have been reached with a small brush but it was only 1/2 inch wide.
with a small brush, just like you said.
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post #12 of 13 Old 01-24-2013, 11:00 PM
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Yes - small brush is what I use and I prefer the flat types you can buy in hobby stores. I put a good amount of glue on a large metal can top and when I'm done, I wash the top and brush in hot water so I can use them again. The metal can top (32 oz can is good) just makes the job faster and less messy.

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post #13 of 13 Old 01-25-2013, 01:24 AM
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Small brush as other have said. I have also used a tongue depressor a few times to get into tight mortices.
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