A question about a mortise and tenon joint. - Woodworking Talk - Woodworkers Forum
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post #1 of 23 Old 10-01-2020, 10:09 AM Thread Starter
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A question about a mortise and tenon joint.

I learned from my Dad, and he was self taught decades before anyone could watch youtube videos. He used a lot of screws to join two pieces of wood. The end result is I am now attempting my first M & T table build, (16"D X 32"L X 35"H).

I'm comfortable that I can do it, but I do worry about accurate fit. In watching many videos, I see two different ways to fit the pieces together. First is with a tight fit on all four sides and the second is to make the tenons a bit shorter top and bottom to allow slight movement up and down for a better fit. (I am assuming the width of the board is vertical.) This is very appealing for someone's first try, but it seems that it would sacrifice strength. The tenons will be 4" on the long side by 3/8" thick by 1" long. Will the joint be "strong enough" if I use the second method?

One more question - how much space should I allow at the bottom of the mortise for the glue that will be forced into the joint as I fit the two pieces together?

Thanx ~ Ron
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post #2 of 23 Old 10-01-2020, 10:32 AM
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Doesn't matter. If you glue the joint in there won't be enough wood movement to affect the joint.

As long as you can dry fit the joint together without forcing it you will be alright. Any excess glue will squeeze out. You might make the tenon about 1/32" short.
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post #3 of 23 Old 10-01-2020, 12:16 PM
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Can we assume your m&t will be done with chisels/hand saws?

There are a number of good YouTube videos that show how to make a proper m&t joint. See Paul Sellers and Rob Cosman.

If I'm reading your methods correctly, you should always keep your mortise width and height the same as your tenon to create a proper joint. If you're not making a through m&t, it doesn't so much matter that the tenon touches the floor of the mortise, as it would be an end-grain glueup, which isn't strong anyway. Making the tenon 1/16 (or even 1/8) shorter than the mortise depth would be acceptable.

https://www.finewoodworking.com/2019...non-variations
On this page you can see the pegged, wedge and tusk methods, which increase the joint strength and durability.

Geoff
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post #4 of 23 Old 10-02-2020, 08:12 AM Thread Starter
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Thanx for the responses gentlemen. I am using a router and table saw to cut these.
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post #5 of 23 Old 10-02-2020, 11:20 AM
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Quote:
Originally Posted by RonBenson View Post
Thanx for the responses gentlemen. I am using a router and table saw to cut these.
In that scenario, I make the mortise and the tenon the same height, and the mortise ends are round because the router made them that way. Then I file the sides of the tenon round to fit. That is of course assuming this isn't a through tenon that will show on the other side.
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post #6 of 23 Old 10-02-2020, 12:21 PM
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i leave the tenon 1/32" shorter a steve suggested, as i want minimum squeeze out, and i want the shoulders to sit flush. i always cut the mortises first, and the tenons (on the ts) to fit, adn i sneak up on it. i find it much easier to trim the tenon than it is the mortise.

you can always pin the mortise with a dowel if you are concerned about strength.
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post #7 of 23 Old 10-02-2020, 02:17 PM
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I would suggest making an adjustable mortise jig for the router. I made this one recently, to make the 40 or so mortises for a dresser. In my opinion it was a few hours well spent, to allow easy and consistent mortising. You can easily find plans on most of the major woodworking magazine sites.

It's basically an open box base, with a fence that holds the workpiece, and a small platform for the router that slides forward and back on two parallel wood strips. The platform is only attached by a t-bolt in the forward/back adjustment slot and a locking knob. The platform has a hole cut out along the path of the router so you can see the mortise.

You cut matching dadoes in the top of the base and the sliding platform, and put the wood strips on the base. There's a fixed stop on the right, and an adjustable on the left. You will find some plans that have you attach your plunge router base to the platform. I simply made two parallel fences that keep the router steady. I made a platform for both of my plunge routers.

Three helpful comments before you start.
1- Use a bit the size of the mortise. It's much easier than making multiple passes to get the proper width.

2- Mark all the mortises from the face of the board. Since this jig references off the edge of the bit, that front mark needs to be consistent.

3-Extend the layout lines for the length of the mortise to the edges of the workpiece. This allows you to line it up with a mark on the jig that shows where the bit starts cutting.

How to use it.

Set your plunge router for the finished depth of cut. Make sure you zero the bit while it's on the platform, otherwise you'll be short the thickness of the platform.

Using a piece of test stock, marked with the mortise width (don't worry about the length), put it face towards the jig (away from you).

Move the platform forward or back, and lock it down when the bit looks like it aligns with the face side (toward the jig) layout line. Make a short cut and adjust the platform forward or back until your cut is at the face side layout line.

Move the router to the right side fixed stop, and make a small plunge just to see where the right side of the bit starts to cut. Mark that on the base (or the platform). This is where you will line up the actual workpieces.

Make a test mortise in several passes of increasing depth (about 1/8" or so, you'll feel what the bit can handle). Check alignment, depth, how the router cuts as you plunge, etc.. If everything went well, move on to your workpieces.

With your workpiece, face towards the jig, align the right mortise layout line with that right side start mark. Next, slide the router to the left until the bit lines up with the left end of the mortise layout line, and set the left stop. Plunge in several passes until you get to the finished depth.

If you have a spiral bits, they make it easier than straight bits because they cut better as they plunge. Straight bits work fine, but since the bottom doesn't cut as well, you have to take smaller passes. It's not a huge issue. I cut 24 1-1/2" deep mortises using a 1/2" straight bit and it was just fine. It just took a little longer than when I used the spiral bit.

I hope this helps.
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Last edited by sanchez; 10-02-2020 at 04:29 PM.
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post #8 of 23 Old 10-03-2020, 06:06 PM Thread Starter
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@Dave Mills - that is my plan except that I will cut the tenons about 1/32" short.
@TimPa - that is what I plan to do.
@sanchez - thanks' for the very detailed response. I did build a jig although it is not as fancy as yours. I felt that using the face of the legs as my reference would be the best way to accurately place the mortises.

Ron
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post #9 of 23 Old 10-03-2020, 10:32 PM
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You're welcome. Awesome, let us know how it goes. Take some pictures along the way.
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post #10 of 23 Old 10-04-2020, 07:47 AM
where's my table saw?
 
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Quote:
Originally Posted by sanchez View Post
I would suggest making an adjustable mortise jig for the router. I made this one recently, to make the 40 or so mortises for a dresser. In my opinion it was a few hours well spent, to allow easy and consistent mortising. You can easily find plans on most of the major woodworking magazine sites.

It's basically an open box base, with a fence that holds the workpiece, and a small platform for the router that slides forward and back on two parallel wood strips. The platform is only attached by a t-bolt in the forward/back adjustment slot and a locking knob. The platform has a hole cut out along the path of the router so you can see the mortise............


I hope this helps.

I love a good DIY shop made mortise jig. I made one myself for a project that required some 30 mortises of different sizes and some times 90 degrees apart on the same piece:
https://www.woodworkingtalk.com/memb...9709-100-2078/



Mine doesn't self-center, but the parallel arms capture the piece so once you do set it on center, all the succeeding mortises will be centered. It uses a Porter Cable edge guide on one of the arms, which has precise adjustments.

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The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 10-04-2020 at 09:29 AM.
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post #11 of 23 Old 10-04-2020, 02:10 PM
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1/32" short on the tenon is not enough.You will soon find out.
A proper fitting tenon will not always allow glue air to escape. You will press in and the air will compress and push it right back out.
It is also hard to put into words about how tight is tight. The best I can do is to say that if the tenon just falls into the mortise, it is too loose.
If you have to use any excessive force, then it is too tight. The glue will be forced out of the joint. It should take nominal pressure, whatever that means. LOL
Anyway, if the joint is too loose, don't panic. You can just glue a piece of veneer onto one or both sides of the tenon. Let it dry before you re-fit. You can make your own veneer with a table saw or band saw. Just make real thin slices.

Question: you gave the dimensions of the tenon but I am not sure which way you are looking at them. if you has a 1x4 horixontally oriented with the 1" side touching the workbench and the 4" side being the height then: The flat surface facing you would be the tenon Face. The top narrow edge would be the tenon edge. The distance from the end of the tenon to the main part of the board would be the tenon length.
Can you please state the dimensions of the tenon again, using the terms I used above so that I will better understand what you have done.
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post #12 of 23 Old 10-05-2020, 08:54 AM Thread Starter
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Thanks @woodnthings and @Tony B .I will take some photos and post in this thread.

Tony - face is 4", edge is 3/8" and length is 15/16, (in a 1" mortise).

And I just had a thought as I was typing this. Would I lose too much strength if I cut perpendicular to the tenon face on the bandsaw to produce a narrow kerf? That would give glue some space to flow but would it be enough to make a difference?

Ron
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post #13 of 23 Old 10-05-2020, 09:55 AM
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Reducing the "hydraulic effect" .......

Just make a shallow "V" groove on one or both of the faces to allow the air and glue to be pushed out when the tenon is a close fit. It won't take much depth, so you can just use a sharp hand chisel at a 45 degree angle on the face running parallel with the long grain. The tenon should be 1/16" shorter than the depth of the mortise also.


You can also make the tenon a bit less wide and leave a gap on either end which won't significantly effect the strength of the glued joint. Here's why:
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post #14 of 23 Old 10-05-2020, 01:45 PM
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I wasn't sure if you were talking about sticking into the mortise 4" deep or 1 inch deep. That is why I questioned it. Looking at the length of the mortise of 15/16", for me that is way to shallow. maybe others dont think so.
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post #15 of 23 Old 10-05-2020, 05:41 PM Thread Starter
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Thanks again @woodnthings and @Tony B. I had thought about a groove but wasn't sure that would work.

15/16 may not be long enough, but the legs are 2" X 2" at the top and will taper to 1" at the floor. I could get a bit more in length if I cut the ends to 45į, but I don think it would help much, and is a bit more than I want to tackle with my first set of M&T joints...

I did finish both parts today and they vary from an fairly easy push to fit to a medium pressure to fit. None drop in or require clamps to get the joint to fit.

Below is a phot of one of the joints and the jig I built to cut the mortises. (Sorry the first photo didn't rotate.)

Ron
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post #16 of 23 Old 10-06-2020, 06:38 PM Thread Starter
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Some progress today... I managed to dry fit the legs and skirts together today and I was pleasantly surprised the the legs are square to the sides and the diagonals are less than 1/32" out.

Since this is my first M&T build, I'm wondering if I should glue up the whole thing, (after some sanding...), or should I glue the ends, (or sides), to the appropriate legs and then glue the other
skirts to the glued up sections? I've seen it done both ways on youtube...

Ron
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post #17 of 23 Old 10-06-2020, 06:54 PM
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Very nice, thanks for the updates!

Thanks for showing your jig I see now that you attached the router directly. Lots of different ways to get it done!
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post #18 of 23 Old 10-07-2020, 09:10 AM Thread Starter
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Thanks @sanchez and you are welcome. I am firmly entrenched in the KISS camp. (That's Keep It Simple Stupid in case anyone isn't familiar with KISS.)

Ron
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post #19 of 23 Old 10-07-2020, 05:02 PM
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I almost always glue up everything all at once.
I first glue the rear apron to 2 legs. Next, the front apron to the other 2 legs.
Then do the end aprons.

This should be done upside down on a perfectly flat surface. It is easier to adjust, take final measurements and check for squareness. To me, the perfect flatness is most important
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post #20 of 23 Old 10-08-2020, 01:02 PM Thread Starter
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Quote:
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I almost always glue up everything all at once.
I first glue the rear apron to 2 legs. Next, the front apron to the other 2 legs.
Then do the end aprons.

This should be done upside down on a perfectly flat surface. It is easier to adjust, take final measurements and check for squareness. To me, the perfect flatness is most important
Thanks Tony - I hadn't thought of doing it upside down, but that should give a good fit.
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