Mortise/Tenon dimensions? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 08-23-2016, 01:09 PM Thread Starter
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Mortise/Tenon dimensions?

Hi, I'm relatively new to woodworking. I'm planning to build a "farmhouse" style dining table 72"x 40" or so. Table top will be roughly 2x8 or 2x10 knotty alder (wife wants a thick tabletop). She also wants breadboards on either end. I was planning on 5" wide breadboards on either end (suggestions for different widths welcome).

I was planning to make my breadboard M&Ts using a plunge router and dado blade. My question is, given the thickness of the tabletop and width of the breadboard, what should the dimensions for my tenons be? Was thinking 2" long, 5" wide, and 1" thick based on what I've read. Suggestions?
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post #2 of 10 Old 08-23-2016, 03:43 PM
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Your dimensions are fine. I would space at least 4 M/T's at each end.
Cutting a 2" dado might be a trick unless you have a large dado blade.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #3 of 10 Old 08-23-2016, 04:06 PM Thread Starter
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Thanks. I figured I'd just make a few passes with a dado on each side and smooth it out?
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post #4 of 10 Old 08-24-2016, 02:31 PM Thread Starter
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On another note (since I'm routing my mortises) do they need to be squared off with a chisel? Is there another way? Do they need to be squared off?
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post #5 of 10 Old 08-24-2016, 06:31 PM
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Originally Posted by Tebluth View Post
On another note (since I'm routing my mortises) do they need to be squared off with a chisel? Is there another way? Do they need to be squared off?
No. You can round over the corners of tenons to easily fit the round of the routed mortise.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #6 of 10 Old 08-25-2016, 03:22 AM
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Generally I cut mortise and tenons roughly 1/3rd the of the work piece if for no other reason than i suck at math. It's just easier than some formula I don't know of. I make them squared just because I use a chisel to cut mortises. If I used a triangular chisel I'd make them triangular I guess.. Maybe not..that doesn't make sense, but it sounds good..

I figured it's time to change my signature so hold your breath. This is it.
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post #7 of 10 Old 09-16-2016, 10:09 PM Thread Starter
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Ok back to the well for some more insight...

Update, turns out we'd like wider breadboards on our table ends. I've got a nice pair of 2x8 poplar boards to use. Unfortunately, I think this means my mortise needs to be about 4.75" long or so. I was planning to make my mortises with a plunge router but I'm not sure they even make bits that would go that deep. I don't have a mortising machine. I could borrow a drill press I suppose.

But before I do that, I realized I could easily rip a 1" wide dado along the long edge of my breadboard and then route out a corresponding tenon along the edge of my table--so a tongue/groove job, basically one big long M&T joint that I could pin with dowels. Is this inherently weaker than the M&T joint? Most forums I read seem to prefer the latter for breadboard ends.
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post #8 of 10 Old 09-16-2016, 11:08 PM
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Ok back to the well for some more insight...

But before I do that, I realized I could easily rip a 1" wide dado along the long edge of my breadboard and then route out a corresponding tenon along the edge of my table--so a tongue/groove job, basically one big long M&T joint that I could pin with dowels. Is this inherently weaker than the M&T joint? Most forums I read seem to prefer the latter for breadboard ends.
As I stated on 8/23, I would space 4 M&T's on each end rather than one single long groove. This seems to allow more for wood movement. The depth of the M&T will work well if you can make them 1 1/4" deep/long.
If you decide to cut one single long dado across the entire length, it will work also but that is a lot of material to align and pull tight when gluing up.
If you shoot the dado completely straight across the end, it will be an open mortise and you will see the tenon on the side. If you use a stopped dado, it becomes a blind mortise and the tenon is not visible from the side. Strength is the same either way.
Good luck.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #9 of 10 Old 09-17-2016, 12:25 AM Thread Starter
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Toolman, so for an 8" wide breadboard, a 1-1/4" deep mortise would be sufficiently long/deep?
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post #10 of 10 Old 09-17-2016, 10:53 AM
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Yes. Your table top is thick and offers a lot of glue surface.
If you think someone may try and stand on the edge and you want additional support, I would add 2 or 3 large diameter oak dowels (about the size of a broom handle) for extra strength. These dowels can be bored to 2" depth.

If you don't have time to do it right the first time, when will you have time to do it over?
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