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M&T fit?

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Forum topic by Travis posted 01-18-2020 08:52 PM 574 views 0 times favorited 16 replies Add to Favorites Watch
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Travis

374 posts in 397 days


01-18-2020 08:52 PM

Hi all,

I am working on the base for a trestle table. First time building a table, and first time doing M&T joinery. I’m trying to make sure my fit is solid between legs and feet before I start the legs to cleats.

Try as I might, I cannot get a tighter fit than this. Is this typical, something to just fill in with a dab of filler? I tried shaving off just a hair on the inside of the tenon to encourage the outside to sit perfectly flush. It doesn’t seem to have helped all that much. I’ve double checked that my depth is okay.

I’m not sure how much energy to put into tweaking this, especially since I think I’m as likely to make things worse the more I fiddle with it. I doubt anyone will see unless they get eye level with the floor.

What do you think? What would you do?

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


16 replies so far

View chuk's profile

chuk

6 posts in 29 days


#1 posted 01-18-2020 09:21 PM

Hi Travis, I’m by no means an expert, but I’ve often found that happens to me when I haven’t cut the shoulder perfectly square to the face. That causes the part of the shoulder closest to the tenon to be every so slightly longer than the portion closest to the face of the board, and it gaps a little. I usually just bevel the shoulders in just a tad with a chisel and it sits tighter. Not positive that’s what’s happening, but just a thought. Perhaps that’s what you meant when you said you shaved a little off the inside of the tenon. I also usually pin mine, which tightens it up considerably. That being said, those look great, and as you say, I’d bet no one would ever notice that small of a gap under a table.

View Mike_D_S's profile

Mike_D_S

603 posts in 2845 days


#2 posted 01-18-2020 09:34 PM

Travis,

It’s certainly possible to get a completely tight M&T joint. Looking at your pics, it looks like the gap is all the way around, so there’s just a few things to check.

1. Make sure the mortise is deep enough for the tenon everywhere. It’s not uncommon to have a mortise bottom that is not perfectly level and even a couple of mm in a tight mortise could cause this. Check the depth in a bunch of places. Taking a little off the tenon length won’t impact the joint strength.

2. The shoulder of your tenon is not really square and level. Use a combination square and double check everthing.

3. Hit it harder. Sometimes in a nice tight mortise, the difference between a beautiful almost invisible seam and a gap is just how much force you use to close it up.

If none of those help, then you have three choices:
1. Forget about it. Anybody who comes in your house, climbs under your table and then mentions the gap is not your friend and should be banned on social media.
2. Use a little filler. The only person who will ever know is you.
3. Cut some very thin strips. Scab glue the strips to the tenon shoulder all the way around and when you close the joint it’ll be nearly impossible to tell you did something.

Mike

-- No honey, that's not new, I've had that forever......

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Mike_D_S

603 posts in 2845 days


#3 posted 01-18-2020 09:36 PM

Also would mention the scab method is also how you cure a tenon that is cut too thin or a mortise cut too wide. You cut a piece and glue it long grain to long grain to the side of the tenon and then cut the tenon to thickness again.

-- No honey, that's not new, I've had that forever......

View Andybb's profile

Andybb

2486 posts in 1234 days


#4 posted 01-18-2020 09:52 PM

+1 What they said. One step at a a time. You are only an adjustment or two away. Nice work for your first try. After first making sure the tenon isn’t too long I’d make sure the shoulders are square. They look level so if the tenon isn’t too long then a little chisel work at the base of the tenon should do the job. 90 % sure that’s your problem. As long as there is glue in the joint you can also rub it with fine sawdust from the same wood.

Or forget it.

-- Andy - Seattle USA

View Travis's profile (online now)

Travis

374 posts in 397 days


#5 posted 01-18-2020 10:04 PM


Hi Travis, I m by no means an expert, but I ve often found that happens to me when I haven t cut the shoulder perfectly square to the face. That causes the part of the shoulder closest to the tenon to be every so slightly longer than the portion closest to the face of the board, and it gaps a little. I usually just bevel the shoulders in just a tad with a chisel and it sits tighter. Not positive that s what s happening, but just a thought. Perhaps that s what you meant when you said you shaved a little off the inside of the tenon. I also usually pin mine, which tightens it up considerably. That being said, those look great, and as you say, I d bet no one would ever notice that small of a gap under a table.

- chuk

Thanks chuk,

Yes, that’s what I meant—should have said I shaved a little off the inside shoulder, not the tenon ;)

When I shaved off the shoulder I didn’t truly bevel, just took a little off the inside. So it may be that I didn’t bevel far enough out. I’ll give that another try.

The way the gap goes around all 4 sides, I’m inclined to think that’s the problem (unless my mortise is too shallow, as Mike and Andy mention).

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

View Travis's profile (online now)

Travis

374 posts in 397 days


#6 posted 01-18-2020 10:08 PM



Travis,

It s certainly possible to get a completely tight M&T joint. Looking at your pics, it looks like the gap is all the way around, so there s just a few things to check.

1. Make sure the mortise is deep enough for the tenon everywhere. It s not uncommon to have a mortise bottom that is not perfectly level and even a couple of mm in a tight mortise could cause this. Check the depth in a bunch of places. Taking a little off the tenon length won t impact the joint strength.

2. The shoulder of your tenon is not really square and level. Use a combination square and double check everthing.

3. Hit it harder. Sometimes in a nice tight mortise, the difference between a beautiful almost invisible seam and a gap is just how much force you use to close it up.

If none of those help, then you have three choices:
1. Forget about it. Anybody who comes in your house, climbs under your table and then mentions the gap is not your friend and should be banned on social media.
2. Use a little filler. The only person who will ever know is you.
3. Cut some very thin strips. Scab glue the strips to the tenon shoulder all the way around and when you close the joint it ll be nearly impossible to tell you did something.

Mike

- MikeDS

I like your recommendations for what to do if I can’t fix it. At the end of the day, it’s not a big deal :)

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

View Travis's profile (online now)

Travis

374 posts in 397 days


#7 posted 01-18-2020 10:10 PM



+1 What they said. One step at a a time. You are only an adjustment or two away. Nice work for your first try. After first making sure the tenon isn t too long I d make sure the shoulders are square. They look level so if the tenon isn t too long then a little chisel work at the base of the tenon should do the job. As long as there is glue in the joint you can rub it with fine sawdust from the same wood.

Or forget it.

- Andybb

Thanks Andyb! I’ll take another whack at it.

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

View SMP's profile

SMP

1736 posts in 536 days


#8 posted 01-18-2020 10:11 PM

Another thing on non-through M&T is I bevel all the edges on the end of the tenon. Sometimes there is just something in a corner keeping it from seating. Also helps with too much glue that gets trapped. Undercutting the shoulders just slightly, so only the show edges need to fit tight. And drawboring can also help pull it tighter.

View Travis's profile (online now)

Travis

374 posts in 397 days


#9 posted 01-18-2020 10:19 PM



Another thing on non-through M&T is I bevel all the edges on the end of the tenon. Sometimes there is just something in a corner keeping it from seating. Also helps with too much glue that gets trapped. Undercutting the shoulders just slightly, so only the show edges need to fit tight. And drawboring can also help pull it tighter.

- SMP

I think I will drawbore, or at least pin, to give them some extra reinforcement (these are my first M&Ts, after all). I am a little concerned though that I will mess up the fit when I do that.

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

View Andybb's profile

Andybb

2486 posts in 1234 days


#10 posted 01-18-2020 10:22 PM

Yep. That too. 5 mins with a chisel and you’re good to go. Good work.


I am a little concerned though that I will mess up the fit when I do that.

- Travis

Yep. That also. I’d fix the fit and glue and clamp it well and be done. After it’s dry if you want to put a dowel through it, do that.

-- Andy - Seattle USA

View Aj2's profile (online now)

Aj2

2680 posts in 2428 days


#11 posted 01-19-2020 03:29 AM

The shoulder of the tenon needs to be undercut slightly. This will improve the fit and strength.
One way to check is to slide a piece of paper in there to see how far you need to go.
Or where it’s touching

Good Luck

-- Aj

View Mike_D_S's profile

Mike_D_S

603 posts in 2845 days


#12 posted 01-19-2020 02:06 PM

AJ has a good point. If paper won’t work ten try a thin feeler gauge and see if you can get to the tenon all the way around (which means the mortise bottom needs work) or you’ll find the bit that is landing early feeling around.

-- No honey, that's not new, I've had that forever......

View splintergroup's profile

splintergroup

3279 posts in 1853 days


#13 posted 01-20-2020 03:53 PM

The undercut method is a classic way to get the tight joints. Looking at the photos. could the end of the tenon board be slightly rounded over?

I wouldn’t use filler since it tends to flake out when used at joints.

View Travis's profile (online now)

Travis

374 posts in 397 days


#14 posted 01-22-2020 02:22 AM



The undercut method is a classic way to get the tight joints. Looking at the photos. could the end of the tenon board be slightly rounded over?

I wouldn t use filler since it tends to flake out when used at joints.

- splintergroup

I’m glad you brought that up because I was wondering that myself. I usually round all my edges but I assumed one normally kept those edges sharp. Do people generally round over those mating edges? Would it look weird if I did?

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

View WoodES's profile

WoodES

162 posts in 2321 days


#15 posted 01-22-2020 03:59 AM

Another method is to chamfer the edges of the visible end of the piece and let the gap show as uniform space. Takes your eye away from any imperfections….

showing 1 through 15 of 16 replies

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