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Squaring up M&T joints

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Forum topic by Travis posted 11-12-2019 04:55 AM 460 views 0 times favorited 18 replies Add to Favorites Watch
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Travis

349 posts in 333 days


11-12-2019 04:55 AM

I’m in the process of making a trestle table and it’s my first time using mortise and tenon joints. I’m working on attaching the legs to the feet and the cleats. The mortises are 2 inches deep by 2 inches long and 1.5 inches wide. Because of their depth I wasn’t able to use a router, so I dug most of it out with a forstner bit and cleaned up the sides with chisels. I made the tenons with a tenoning jig on the table saw. The tenons are true, the mortises pass the visual test though they are not perfect. I having been working both the mortises and the tenons to get a passable fit and I noticed that while I can wiggle the tenons in most of the way (about 90%), they do not go in straight.

I can continue to lightly remove material from either tenon or mortise to allow the tenons to slide in easier and eventually sit square on the shoulders, but I know the strength of the joint doesn’t come from the shoulders—it comes from the tight glue bond on the long grain of the tenon. So I don’t want to loosen it so much that it weakens the joint.

As these are my first M&T, I don’t know if what I am experiencing is normal. Do you have any recommendations for how to proceed? It’s really hard for me to tell where the obstructions may be because I can’t see in the joint when I’m fitting it (obviously). When it was sitting askew I removed small shavings from the acute side assuming something there was pushing it the other way. That helps bring the leg back in the right direction but a bit too far, kind of like I’m see-sawing. Which maybe suggests the joint is already too loose, though it is tight enough that I can’t get the tenon all the way in with hand pressure. The angle doesn’t look way off, it’s just over the span of a 2 foot leg, that error is magnified pretty big and alignment is critical since the legs are joined on the top and bottom.

Any suggestions?

-- The plan is wrong; my finished piece is right.


18 replies so far

View pintodeluxe's profile

pintodeluxe

6017 posts in 3380 days


#1 posted 11-12-2019 05:52 AM

Your mortises are probably at fault, so adjust your mortises with files or sanding sticks until the tenon fits well.
Can you cross-peg the joint with a small dowel?
It would add some extra strength.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View therealSteveN's profile

therealSteveN

4348 posts in 1141 days


#2 posted 11-12-2019 06:00 AM

Most people know the cheat to use a Combination square to check for depth, but you can also tell if you have wall faults down in a mortise, where the walls aren’t true. Might need to push, and pull or wiggle it around some, but you can tell if you have obstacles, and where.

Careful about how loose you start getting everything, or drawboring may be your only recourse. If you’ve seen a Festool Domino, they have a little movement side to side, but front to back they are fairly snug, start getting sloppy, and it’s Drawbore, or wiggle.

-- Think safe, be safe

View JerryMaldonato's profile

JerryMaldonato

46 posts in 890 days


#3 posted 11-12-2019 02:55 PM

Listen to therealSteveN. He knows more about woodworking than most people on here combined.

View SMP's profile

SMP

1468 posts in 472 days


#4 posted 11-12-2019 02:56 PM

It can also depend on the show side etc. This is a pretty good article/video on it. Richard has some other related blog posts as well:
https://www.theenglishwoodworker.com/mortice-and-tenon-fitting-by-hand/

View Travis's profile

Travis

349 posts in 333 days


#5 posted 11-12-2019 03:00 PM



Your mortises are probably at fault, so adjust your mortises with files or sanding sticks until the tenon fits well.
Can you cross-peg the joint with a small dowel?
It would add some extra strength.

- pintodeluxe

I can definitely add dowels. Thanks for the suggestion of files, that sounds a lot easier than what I have been trying.

-- The plan is wrong; my finished piece is right.

View Travis's profile

Travis

349 posts in 333 days


#6 posted 11-12-2019 03:09 PM



Most people know the cheat to use a Combination square to check for depth, but you can also tell if you have wall faults down in a mortise, where the walls aren t true. Might need to push, and pull or wiggle it around some, but you can tell if you have obstacles, and where.

Careful about how loose you start getting everything, or drawboring may be your only recourse. If you ve seen a Festool Domino, they have a little movement side to side, but front to back they are fairly snug, start getting sloppy, and it s Drawbore, or wiggle.

- therealSteveN

Thanks therealSteveN! I have been using the combination square and I can see where my walls deviate from perfect square. But I have been hesitant to square them all up because that would mean increasing my mortise on all 4 sides and I worry that will make my mortise too big.

On the other hand, if drawboring is a viable solution it would be quicker than getting these to fit perfectly….

-- The plan is wrong; my finished piece is right.

View Travis's profile

Travis

349 posts in 333 days


#7 posted 11-12-2019 03:09 PM



It can also depend on the show side etc. This is a pretty good article/video on it. Richard has some other related blog posts as well:
https://www.theenglishwoodworker.com/mortice-and-tenon-fitting-by-hand/

- SMP

Thank you for that resource!

-- The plan is wrong; my finished piece is right.

View bilyo's profile

bilyo

910 posts in 1669 days


#8 posted 11-12-2019 04:03 PM

I suggest that you get the mortises squared up even if it makes them a bit too large. Then you can glue thin veneer shims onto the tenon as needed to get a snug fit. This will allow you to make sure the leg is straight and also get a snug fit.

Another hint: As you are test fitting, apply some marks across the tenon faces with chalk or a soft pencil. Then, as you insert and remove the tenon, the tight spot will make a rub mark through the chalk or pencil lines and you can tell where to remove a bit more material.

View Travis's profile

Travis

349 posts in 333 days


#9 posted 11-12-2019 09:45 PM



I suggest that you get the mortises squared up even if it makes them a bit too large. Then you can glue thin veneer shims onto the tenon as needed to get a snug fit. This will allow you to make sure the leg is straight and also get a snug fit.

Another hint: As you are test fitting, apply some marks across the tenon faces with chalk or a soft pencil. Then, as you insert and remove the tenon, the tight spot will make a rub mark through the chalk or pencil lines and you can tell where to remove a bit more material.
- bilyo

That’s comforting to know I can always make the tenon a little bigger with veneer.

-- The plan is wrong; my finished piece is right.

View TungOil's profile

TungOil

1356 posts in 1062 days


#10 posted 11-13-2019 03:03 AM

Probably too late for this project, but Jeffrey Miller did a great mortising block in Issue 172 of Fine Woodworking that you might consider making for future projects. His jig utilizes a plunge router and works really well. If you need a deeper mortise than you can cut with a router you can always cut what you can with the router then bore the remaining waste out with a Forster bit, then cleanup with a chisel using the routed sides as a guide to get a nice square mortise wall. Also, a cabinetmakers float works really well for fine tuning the joint.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View TEK73's profile

TEK73

278 posts in 274 days


#11 posted 11-13-2019 05:15 AM

Using drawboring works quite well as it draws the jointed pice tight until the shoulder. Also, shims is a good solution if you make the holes a bit to big.
I do however often need to use some force (rubber mallet) to get the joint to close – but that might be wrong, I’m not that experienced.

-- It’s good to have an end to journey toward; but it is the journey that matters, in the end. - Ursula K. LeGuin

View Travis's profile

Travis

349 posts in 333 days


#12 posted 11-13-2019 05:46 AM



Probably too late for this project, but Jeffrey Miller did a great mortising block in Issue 172 of Fine Woodworking that you might consider making for future projects. His jig utilizes a plunge router and works really well. If you need a deeper mortise than you can cut with a router you can always cut what you can with the router then bore the remaining waste out with a Forster bit, then cleanup with a chisel using the routed sides as a guide to get a nice square mortise wall. Also, a cabinetmakers float works really well for fine tuning the joint.

- TungOil


That’s an interesting solution to getting the walls nice and square. I have several more to cut so I may give that a try. Thanks!

-- The plan is wrong; my finished piece is right.

View Travis's profile

Travis

349 posts in 333 days


#13 posted 11-13-2019 05:49 AM



Using drawboring works quite well as it draws the jointed pice tight until the shoulder. Also, shims is a good solution if you make the holes a bit to big.
I do however often need to use some force (rubber mallet) to get the joint to close – but that might be wrong, I’m not that experienced.

- TEK73

Well, you are more experienced than me ;) My challenge is I find it difficult to test fit if I have to mallet them in there. Pulling them out is no walk in the park. I about gave myself a blackeye yesterday because I was trying to pull one out so hard it finally came back and knocked me in the brow. 2.5”x3”x24” solid ash to the face…. It was a sight out of a cartoon.

-- The plan is wrong; my finished piece is right.

View bondogaposis's profile

bondogaposis

5573 posts in 2918 days


#14 posted 11-13-2019 01:01 PM

Sometimes there are little bits that are in the corners of the mortise that are hard to remove and prevents the joint from closing properly. An easy fix is to chamfer the ends of the tenon, that also gives some room for any excess glue.

-- Bondo Gaposis

View Travis's profile

Travis

349 posts in 333 days


#15 posted 11-13-2019 02:56 PM



Sometimes there are little bits that are in the corners of the mortise that are hard to remove and prevents the joint from closing properly. An easy fix is to chamfer the ends of the tenon, that also gives some room for any excess glue.

- bondogaposis

Thanks for the idea Bondo! I have chamfered the edges a little. It did help but I think they need some more work :(

-- The plan is wrong; my finished piece is right.

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