A question about Mortise and Tenon Joints

[mountainbreeze]

I'm building myself a new workbench and with it, I'm experimenting with mortise and tenon joints. My question is this: When dry fitting the M/T joint, how loose/tight should it be? Right now, I can push them together with a little help from a rubber mallet. Will this be too tight with glue applied?

[dusty]

I'm building myself a new workbench and with it, I'm experimenting with mortise and tenon joints. My question is this: When dry fitting the M/T joint, how loose/tight should it be? Right now, I can push them together with a little help from a rubber mallet. Will this be too tight with glue applied?

That really depends on how big your rubber mallet is.

Even without glue, the joint should be very snug. But yes, you can get the fit too snug. I suggest that you cut and glue a test joint. Also remember, a joint that fits today may be too tight (or too lose) tomorrow.

[charlese]

I'm building myself a new workbench and with it, I'm experimenting with mortise and tenon joints. My question is this: When dry fitting the M/T joint, how loose/tight should it be? Right now, I can push them together with a little help from a rubber mallet. Will this be too tight with glue applied?

Sounds just about right to me, as long as the shoulders fit nicely! Sliding in and out like a drawer is too lose for a good joint.

[8iowa]

I've had trouble with dowels fitting after the glue was applied. This can be a frustrating problem because you are "on the clock" in regards to the glue drying. I would loosen the tennons until they can be fit by hand only. Then, after applying the glue you will likely need that rubber mallet.

[jimsjinx]

When I make a tennon joint, I always make them snug. I also pre saturate the glue surfaces with a little H2o to wake up the grain. If it gets too tight, I'll pare a tiny bit of material and re-fit. Now when coated with glue, it soaks right in, and I get even squeeze-out all the way around. I have never had a joint pull apart in 35 years. Tightbond 2 and 3 are my glues of choice. If I had one piece of advise, it would be to make sure the tennon does not rest against the bottom of the mortise. I always leave about a 16th of clearance for glue at the bottom. Also, if the tennon is wider than about 3 inches, split the tennon in the middle. This will allow the board to split under pressure a tiny bit at the shoulder, but the joint will NOT pull apart. jimsjinx

[dusty]

When I make a tennon joint, I always make them snug.

I also pre saturate the glue surfaces with a little H2o to wake up the grain.
To pre-saturate - does that mean dip it, spritz it or wipe it with a wet rag?

If it gets too tight, I'll pare a tiny bit of material and re-fit. Now when coated with glue, it soaks right in, and I get even squeeze-out all the way around. I have never had a joint pull apart in 35 years.
Does the glue soak in because the wood was wetted before glue application?

Tightbond 2 and 3 are my glues of choice. If I had one piece of advise, it would be to make sure the tennon does not rest against the bottom of the mortise. I always leave about a 16th of clearance for glue at the bottom.

Also, if the tennon is wider than about 3 inches, split the tennon in the middle. This will allow the board to split under pressure a tiny bit at the shoulder, but the joint will NOT pull apart. Is this like a bandsaw kerf up the middle of the tenon?

jimsjinx

I embedded my questions in blue hopefully to eliminate confusion caused by the questions.

I am interested in this discussion because I have always avoided (for no good reason other than habit) getting the wood wet before glueing.

[jimsjinx]

I read in an article about gluing that wetting the wood starts the cells drawing in moisture, and when the glue hits the same moist cells, a tiny border of thinned glue,(due to the water), will be absorbed deeper into those wood cells/fibers. Glue right outa the bottle, does the same thing, but to a lesser degree, cause the glue is thicker. I have even used a thinned glue to pre wet the joint. As far as how much, I just dip my glue brush in water, and wet the joint slightly. I have thinned epoxy with denatured alcohol as well, to get super absorbsion of the adhesive. Model airplane kits instruct you to do this all the time, for added strength. Just before the thinned epoxy sets up, I brush on a coat of unthinned epoxy, and I have gotten some incredibly strong joints that way. As far as the split tennons, I take a little square of material out of the middle. For example, in a 6 inch long by 1/2 inch thick tennon, I'd take an inch there abouts out of the middle of the tennon. The 2 mortises needed now are separate, not just one big hole. More work, yes, but VERY strong and lasting. There is a sawdust session on this same deal, somewhere. It allows the wood to move a bit with moisture fluctuations, and the joint won't fail. You may get a check/split in the middle, at the end, but it will be small, and stop. If you glue the whole thing solid, with no notch, the board the tennon is made from will force the glue joint into a shearing action that can, and has, sheared the glueline, thus the joint can come apart. If I can find that sawdust session that addresses this subject, I'll post it. I learned it years ago, but saw that session not long ago. I think it was titled mortise and tennon joints. Try the water thingy out on some scrap. Allow a longer cure time, and you'll see the glue gets drawn in deeper than without. I did the same thing on the "Bed from Hell" as I call it. The sideboards had to stay super low to the floor, and the headboard is 6' tall! And heavy! It could hurt someone if the thing came apart. I didn't want the M&T joints to ever budge! jimsjinx

[dusty]

I read in an article about gluing that wetting the wood starts the cells drawing in moisture, and when the glue hits the same moist cells, a tiny border of thinned glue,(due to the water), will be absorbed deeper into those wood cells/fibers. Glue right outa the bottle, does the same thing, but to a lesser degree, cause the glue is thicker. I have even used a thinned glue to pre wet the joint. As far as how much, I just dip my glue brush in water, and wet the joint slightly. I have thinned epoxy with denatured alcohol as well, to get super absorbsion of the adhesive. Model airplane kits instruct you to do this all the time, for added strength. Just before the thinned epoxy sets up, I brush on a coat of unthinned epoxy, and I have gotten some incredibly strong joints that way. As far as the split tennons, I take a little square of material out of the middle. For example, in a 6 inch long by 1/2 inch thick tennon, I'd take an inch there abouts out of the middle of the tennon. The 2 mortises needed now are separate, not just one big hole. More work, yes, but VERY strong and lasting. There is a sawdust session on this same deal, somewhere. It allows the wood to move a bit with moisture fluctuations, and the joint won't fail. You may get a check/split in the middle, at the end, but it will be small, and stop. If you glue the whole thing solid, with no notch, the board the tennon is made from will force the glue joint into a shearing action that can, and has, sheared the glueline, thus the joint can come apart. If I can find that sawdust session that addresses this subject, I'll post it. I learned it years ago, but saw that session not long ago. I think it was titled mortise and tennon joints. Try the water thingy out on some scrap. Allow a longer cure time, and you'll see the glue gets drawn in deeper than without. I did the same thing on the "Bed from Hell" as I call it. The sideboards had to stay super low to the floor, and the headboard is 6' tall! And heavy! It could hurt someone if the thing came apart. I didn't want the M&T joints to ever budge! jimsjinx

Thank you. I will give this a try.