Mortise and Tenon ?

[Mike Gresham]

I'm building my first project with M&T joinery. I discovered I have no idea how tight the joints should be before glue-up. It doesn't seem like they should need to be driven with a hammer, Glue being water based would swell the wood a little and could make it impossible to seat the tenon. So, how tight is correct and how do you judge it?

[Alan Lilly]

For me... it should have no wobble or slack, but shouldn't be tight. It should be a slip-fit. It should slide easily together with mild friction and little effort. Like you said... the glue will do its job and tighten the joint quickly.

[pat warner]

If you can measure to a mil: Slop should be ~.001" - .003" unless you're using some hardware for slop insurance.

[mike holden]

It should go together, dry, with light hand pressure. Just enough that it wont fall apart when you turn it over.

[Prashun Patel]

FWIW, in my experience, the glue usually functions as a lubricant to make joints slide better together, so err on the side of a tighter fit if you have to. The swelling is minimal and almost never something that can't be overcome with clamps.

[Larry Edgerton]

FWIW, in my experience, the glue usually functions as a lubricant to make joints slide better together, so err on the side of a tighter fit if you have to. The swelling is minimal and almost never something that can't be overcome with clamps.

I am in this camp. The swelling is going to go away, so if the joint is not reasonably snug when all is said and done you are dependent on too much glue for my liking. Besides, how long does it take to assemble a joint, and does the wood really swell appreciably in that short amount of time?

In the old days when building barns the verticals with the mortices were often put up green [swelled] and the horizontals were installed dry [shrunk] so when it all reached an equilibrium the joints were extremely tight. I borrow from this idea sometimes and wet the mortice area thoroughly a bit before I glue up. Not sure if it actually swells the piece in the half hour I allow but it does give me a bit more time for glueup and has worked well for me.

Larry

[Charles Lent]

+1. I always try to make them so I can dry fit the joint together snugly, but with no tools, just my hands but they shouldn't fall apart during dry assembly. If they require clamps to pull them together after the glue is added that's OK, but they shouldn't require a dead blow hammer. All of my mortices and tenons are now done using a Leigh FMT Pro and it's easy to adjust for this kind of repeatable fit.

Charley

[Keith Hankins]

My rule of thumb is, you should not have to drive it in with a hammer, and it should not fall out when together without glue. Also, leave a gap at the bottom for glue relief, or you will get a blowout on assembly.

I know I got it right, when it has a little suction when separated. I also champfer my ends on all four sides.

[glenn bradley]

Mostly agree with what has been said. Should take a little hand pressure to get it together and apart. Remember the immortal words of Sam Maloof "leave room for the glue!".

[mreza Salav]

What said. Aim for a very tight fit initially, then a few strokes of sand paper (with hand) will dial it to a perfect fit.
It's much harder to fix "a little" loose fit.

[Mike Gresham]

Thanks for all the responses folks. I have 44 joints to make and this info helps a lot.

[Tom M King]

Iwasaki files help a lot with final fitting. I like to be able to push them together with some effort, and use a urethane mallet to dissassemble. When making sash, sometimes you need to put them together and then take back apart several times in the process. The soft mallets are great for this.

I have one sash that I've probably put together and taken apart a hundred times. I always ask if there is an engineer in the crowd, and have the engineer handle the sash to tell that indeed it is very strong even without pegs. Glue was never intended for these sash-reproductions of 18th Century sash.

found a link to the mallet I use: http://www.sorbothane.com/sorbothane-soft-blow-mallet.aspx

[Robert Engel]

What works best for me is a combination of a large shoulder plane and small block plane to dial in the tenons.
One day I'll get a rabbet plane. If you do it this way set the blades light - and I mean light.

I don't like using files. In my hands I can't maintain a flat tenon.

I also wouldn't use sandpaper because you're going to have to get into the cheek corner and I would be scared of marring the edges if I hit them.

Good luck. By the 41st joint you'll be pretty darn good!!:rolleyes:

If you want to file them, I would check into a tool called a joinery float.
I've seen Phillip Rowe use them. Lie Nielsen sells them.

[paul cottingham]

Start tight enough that it takes force to put them together. I use a shoulder plane or a wide chisel to remove a shaving or two, until they slide together and don't fall apart with gravity. Glues takes care of the rest.

[John Lankers]

I rout the mortises and mill floating tenons to fit extremely tight, then I go and compress the tenons in a metal working vise to make them go in and out easy. The water in the glue then lets them swell back up to their original size. I have never had as much as a hair line show. I can squeeze a 1/4" hard maple tenon down by 0.2 mm which makes assembly very manageable.