# It has been asked...



## rrich (Jun 24, 2009)

How tight should a mortise and tenon joint be?

I could never think of the correct way to express the answer in simple terms. Then yesterday in the shop it hit me like like a two pound dead blow mallet.

Drill a 3/8" hole into the end grain of a piece of scrap oak, about an inch deep. Now insert a two inch fluted 3/8" dowel into the hole. There you have it, as close as possible to describe the correct fit of a M & T joint.


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## Leo G (Oct 16, 2006)

Actually, I think that is a bit to tight. I make my M&T joints so that they are snug but not tight. You should be able to slide it in easily but it should have very little, if no slop on it's width. You need to have room for glue. If you are making a glueless M&T then make the height of the tenon close to the height of the mortise. This will prevent rocking later in the life of the joint. You must remember to take account for the expansion of the tenon in very wide tenons.


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## WarnerConstInc. (Nov 25, 2008)

What about loose mortise and tennons?


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## Leo G (Oct 16, 2006)

What you talking about Willis?


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## WarnerConstInc. (Nov 25, 2008)

Leo G said:


> What you talking about Willis?


 
He he, I forgot a word.:laughing:


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## Leo G (Oct 16, 2006)

Makes a little more sense now. Never used them. You got a Festool you need to push?


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## WarnerConstInc. (Nov 25, 2008)

Leo G said:


> Makes a little more sense now. Never used them. You got a Festool you need to push?


Nah, that will be my next buy though.

It is darn expensive but, darn nice as well.

I have used it to pre-assemble window and door casings. Will be easier now that they came out with a 4mm cutter.

It has 3 settings for snug up to sloppy.


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## Leo G (Oct 16, 2006)

Domino, right? I have seen one and put a tenon/biscuit in a hole. It was a pretty snug fit.

Gee, I guess I have seen a loose tenon.


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## WarnerConstInc. (Nov 25, 2008)

See my edit Leo, it has 3 settings for how tight you want it to be.

I still can't believe how well the old through tennon's with pins hold up.


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## Leo G (Oct 16, 2006)

I guess you're slow on the draw today. What is it, about $700? If I was building more furniture, tables in particular, I would probably invest in one. I had a hard time spending $800 on a Kreg Foreman, but now that I have it, it was well worth it.


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## WarnerConstInc. (Nov 25, 2008)

$825.00 for the set with cross stop and trim stop and 5mm cutter.

Add $260.00 to get a box with all the cutters, 4,6,8,10 mm and 1100 tenons.

Just another 1100.00 bucks, who's counting?


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## rrich (Jun 24, 2009)

Leo G said:


> Actually, I think that is a bit to tight. I make my M&T joints so that they are snug but not tight. You should be able to slide it in easily but it should have very little, if no slop on it's width. You need to have room for glue. If you are making a glueless M&T then make the height of the tenon close to the height of the mortise. This will prevent rocking later in the life of the joint. You must remember to take account for the expansion of the tenon in very wide tenons.


OK Leo, how about a "V" size bit then?


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## Leo G (Oct 16, 2006)

I still think a "V" bit would be to tight. Go up to a "W". I always use a 25/64" for a 3/8" dowel.


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## skymaster (Oct 30, 2006)

"Fluted" dowels :} Isnt that exactly what the flutes are for? :}:}:} 
The glue spreads thru the flutes, covers the dowel and its mating critter without the need to drill oversized? :shifty::shifty:


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## cabinetman (Jul 5, 2007)

I'm not wanting to break up a conversation, but just to add something.:yes: IMO, the mortise for either a dowel or a tenon that isn't fluted should be a very close fit, but a slip fit with minor friction. If the fit is tight enough to scrape the mortise, it will scrape the glue and trap air, resulting in a form of compression. 

This can keep from seating the dowel/tenon, and could just push it back out. There has to be a place for the glue and air to go.


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## GeorgeC (Jul 30, 2008)

cabinetman said:


> I'm not wanting to break up a conversation, but just to add something.:yes: IMO, the mortise for either a dowel or a tenon that isn't fluted should be a very close fit, but a slip fit with minor friction. If the fit is tight enough to scrape the mortise, it will scrape the glue and trap air, resulting in a form of compression.
> 
> This can keep from seating the dowel/tenon, and could just push it back out. There has to be a place for the glue and air to go.


Yes!

G


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