# Need help with gluing M&T joint.



## dan-o (Sep 20, 2012)

*Need help with gluing Loose M&T joint.*

Hi guys, new to the forum. I've been lurking and reading for quite a while but haven't had a reason to sign up until now. I'm working on my first "real" piece of woodworking in the form of a craftsman inspired mirror frame. I've attached a picture of the mockup I made earlier out of some pine and scrap cedar strips. The final version consists of a cherry frame and Peruvian walnut for the accent detail.

I'm using loose tenon joinery to join the rail and style. I thought everything was going well until I did some reading today on gluing the joint together. I was reading that if the mortise is pretty close to the end of the piece on the style, it was best to keep extra material there and then trim to the desired length after glue up to help prevent splitting. I didn't account for this, and all my pieces are exact length. The mortise ends approximately .5" from the end of the style. 

Any thoughts? Will clamping the ends of the styles while gluing help to prevent the split, or is a split inevitable as the tenon swells up due to being so close to the end? I'm at the point of glue up with the final piece and want to cover my bases.

-Dan


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## Dave Paine (May 30, 2012)

If you are using loose tenons, I would recommend 2 part epoxy for the glue. Yellow glue is not intended to be gap filling. The Titebond III claims it can fill gaps "up to 1/64in", however, best not to try.

Another benefit of epoxy is no swelling of the wood so you should not have stress in the joint while the epoxy sets.

I have not read about leaving extra material to have more stock to resist splitting during gluing due to expansion.

I have done a number of M&T joints and never added extra length. Perhaps I have just been lucky.

Edit - forgot to say this is a nice looking design.


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## dan-o (Sep 20, 2012)

Thanks Dave! I'll try to post up a larger post with some pictures I've taken along the way once it's finished. Might have to recreate some of the points to fill in the timeline gaps.

With regards to the gap filling comment. The loose tenon's are sized to be a snug fit into the mortise. There is no gap along the thickness of them. There is a small gap at each end of the mortise where end of the slot is with a full radius. Are you talking about filling those gaps? I was assuming that it woudn't need to be filled to the brim with glue, as the joint won't be seeing stresses like a dresser or bench would have. My initial plan was to lightly coat the mortise and tenon with glue and assemble, trying not to put any glue onto the shoulder to eliminate some squeeze out. Does this make sense? Would it be a similar process for epoxy?


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## Dave Paine (May 30, 2012)

dan-o said:


> With regards to the gap filling comment. The loose tenon's are sized to be a snug fit into the mortise. There is no gap along the thickness of them. There is a small gap at each end of the mortise where end of the slot is with a full radius. Are you talking about filling those gaps? I was assuming that it woudn't need to be filled to the brim with glue, as the joint won't be seeing stresses like a dresser or bench would have. My initial plan was to lightly coat the mortise and tenon with glue and assemble, trying not to put any glue onto the shoulder to eliminate some squeeze out. Does this make sense? Would it be a similar process for epoxy?


If the tenon is a tight fit in the mortise, then yellow glue is fine. Some folks make these rather loose.

I have never worried about getting glue on the shoulder of the mortise.

I like to see squeeze out with any glue.

I normally apply blue masking tape on either side of the glue line. Easier to clean up. If you use epoxy I consider the masking tape highly beneficial to prevent the epoxy filling the grain around the joint, which can prevent any stain from being consistent.

I use the blue masking tape since I have found it will come off with minimal issues of pulling splinters out of the wood and will not leave any residue. 

The brown masking tape can be very difficult to remove, especially if you clamped over the tape. Sometimes it will leave residue.

If you use epoxy, I recommend having some acetone on hand. It is the only solvent to clean up epoxy. It is so easy to get some epoxy where you did not intend. Been there - done that - too many times.


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## firemedic (Dec 26, 2010)

Don't worry about cracking your work, the amount of moisture imparted to the the pieces from glue is minimal. Your tenons should have a friction fit... not to lose not the tight, obviously both are bad. Hardwood is obviously the best choice for a loose tenon but not essential. How are you cutting the mortices?

Dave, I laughed out loud about the lose tenon thing... :smile: good times...


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## dan-o (Sep 20, 2012)

firemedic said:


> Your tenons should have a friction fit... not to lose not the tight, obviously both are bad. Hardwood is obviously the best choice for a loose tenon but not essential.


I made the tenons out of scrap cutoffs of the Cherry I used in the frame. I also oriented the long grain to match up with the direction of the mortises.



firemedic said:


> How are you cutting the mortices?


I used my router table and a custom fence setup to help support the rail's when I was standing them on end. I'm using different thicknesses for the styles and rails, and doing it this way allowed me to justify everything off the back of the parts, keeping the alignment consistent. It worked out really well. I snapped a few pictures along the way and will need to start a build thread. 


I'm making two identical mirrors and glued one of them up last night. I fine tuned the tenon's to slide in place easily yet not fall out if I flipped the piece over and then put a decent amount of glue over eveything. This morning I unclamped the piece and there were no cracks present! I'll glue the other mirror up sometime this weekend.


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## Wood4Brains (Jul 25, 2012)

> I used my router table and a custom fence setup to help support the rail's when I was standing them on end.


If you do this again, would you mind terribly posting photos so us noobs can see what you are doing? It would really help all of us out who are interested in learning about jigs.

Thanks in advance. :smile:


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## dan-o (Sep 20, 2012)

Wood4Brains said:


> If you do this again, would you mind terribly posting photos so us noobs can see what you are doing?


You're in luck! I took pictures of this when I built the prototype. I'll post them later tonight for you.


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## Midlandbob (Sep 5, 2011)

The problem is often over glueing causing hydraulic damage or messy squeeze out. A mirror frame has very little stress on it especially if you use a bit of silicone to hold the mirror and prevent rattle. 
If the fit is right, only a bit of glue in the mortise will make a clean strong joint. Where there are grater forces, a dowel pined in a hole is good. It can be decorative in view or hidden in back. I put them in while clamps are still on. Square dowel ends look good in some applications.
I have just put in a pin or two in with a pin nailer if I'm sure I won't want to disassemble.


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