Mitered Dominoe Question

[Christophl]

Hi, I' building a 6' long sofa table from Mango and Wenge.  The mango was badly warped and after planing, it's only now 1 1/2" thick.  I plan on using the Dominoe for a continuous grain Mango on the left leg, and Wenge on the right leg.  Not sure what size Dominoe to use (the thickest and longest I can fit in the corner?), and I want to make sure this will be a strong enough joint for this long table.

Thanks guys!
Chris

 

[ChuckM]

Can you provide a sketch what is to be joined together?

 

[smorgasbord]

I plan on using the Dominoe for a continuous grain Mango on the left leg, and Wenge on the right leg.  Not sure what size Dominoe to use (the thickest and longest I can fit in the corner?), and I want to make sure this will be a strong enough joint for this long table.

I'm assuming the grain on the legs runs vertically, and that you're cutting 4 sides of each leg out of one board, with mitered edges such that the outside of each is separated only by the kerf of your saw.

If so, then you don't have to worry about strength. That's long grain to long grain gluing, which should be at least as strong as the wood's shear strength in that direction. What the dominos are for is alignment, so use whatever is convenient for you, making sure to keep the domino closer to the inside corner so that you don't cut the mortises too deep. With 1.5" boards that shouldn't be difficult.

 

[Christophl]

Thanks guys!  Yes, using long grain on both ends, just diff. woods.  Here's what I want, but it sounds exactly like Smorgasbord described so I'm good to go...awesome! lol

 

[ChuckM]

The table is subject to racking based on your sketch (no stretchers).

I'd use two rows of dominoes on each mating piece. The choices of dominoes include 8mm, 10mm or even 6mm, or a combination of them depending on the spacing. Make sure the choice or combination does not cause any blow out.

 

[smorgasbord]

The table is subject to racking based on your sketch (no stretchers).

Yes, that drawing (rotated here I assume) is different what I was describing, which was 4-piece hollow legs (one at each corner).

Since you're essentially doing a "wrap" of side to top to side, ChuckS is right that racking is an issue. It also means that you're NOT gluing long grain to long grain, since it's the ends of each board that are mitered and joined to each other. Unless you're working with much wider boards than you showed in your photograph.

In this case, the domino WILL be the thing that adds strength. At a 38mm stock thickness (about your 1.5"), the max mortise length is about 40mm, maybe 35mm to be safe. The DF500 goes 28mm deep max (for 50mm long tenons), but that could be OK if you double up the tenons - note that the ones closer to the outside can't go as deep. You'll want to try the cuts in some scrap of the same size to be sure. I'd use thicker/longer tenons near the inside corner and shorter/thinner tenons nearer the outside corner (again, watch for cutting through, you'll probably have to place that row more in the middle of the miter).

 

[Christophl]

So sorry for the confusion of the design in the term analogy. Obviously you can pretty much time at this point that I am rather new to the game  [wink]
Racking is what I was worried about, so I’m glad that two rows of dominoes will work. I’ve done a couple practices on a 2x6 in the 40 mm will work on the inner side. I have not practiced or done any second row Domino’s yet. Thank you guys for the help, I definitely don’t want to screw this gorgeous project up!

 

[ChuckM]

If in doubt, glue up scraps or use 2×4 material to make a mock-up and test it out to verify the choice of tenon(s) and the domino settings (fence height & mortise depth) being correct. It's ok to screw up on the mock-up or use it as a warm-up on a critical process.

 

[smorgasbord]

I would also consider adding a "2x4" type member under the top, running across the middle, and dominoed into the two sides. This will act as stretcher to some degree to resist racking, and won't be seen by anyone except rug rats and dogs.

 

[Christophl]

Thanks!  I'll def. do mockups.  What's strange is that I've seen tables built this way at showrooms and they always seemed really stable...maybe they used internal steel brackets or something I didn't see.  I'd love to keep the design as simple as possible.

 

[ChuckM]

I only know of one waterfall (?) coffee table (2" thick or more) built of miters like yours, and the maker used metal splines to reinforce the joint. He routed a stopped groove on the mating pieces, and glued everything together with epoxy. Can't remember if it was steel or aluminum, but the splines ran about 3/4 the width of the table. Not going anywhere, like he said. But having used the DF500 on so many projects -- with zero % of failure, I'm confident that if the joint failed with the double row configuration, it'd be the lumber itself, not the dominoes, that gave way.

 

[Christophl]

So Chuck, are you saying that if I use two rows of dominoes, I should be good to go?

 

[ChuckM]

Yes, two rows of tenons (if you can fit them with proper spacing on the mating surface) will give the highest strength.

 

[Christophl]

Got it, Thanks again Chuck!

 

[Christophl]

Chuck, do you guys ever cut size 12 or 14 longer dominoes into shorter pieces like the 40 mm I am going to need, so you can use a thicker tenon? Or do you just use the right length no matter what the thickness of the tenon  is?

 

[ChuckM]

If they can do the job, I use the stock tenons. If not, I cut my own thicker/longer tenons as required.

 

[Christophl]

Awesome!  Thank you so much Chuck!!

 

[Christophl]

Tried 3 times yesterday and keep not having dominoes line up.  Reversing the domino on the leg part keeps screwing me up, esp. on the ends.  This was def. harder than anticipated  :

 

[ChuckM]

Chris,

That was part of the learning curve. The DF is deceivingly an easy machine to master like a dowel centering jig. It isn't due to factors related to the machine itself and user experience.

Did you use the tight width setting for all the mortises? If so, retry on a scrap with tight setting only on the first mortise of each row on the mating pieces. Use the second (middle) width setting for the rest (make sure the machine is running (BUT NOT BEING PLUNGED) when you change the width setting -- read the manual first if you have never done any changing of the width setting before).

Also hold the machine steady and tight when mortising. If the machine moves a hair, so will the mortise. (My preferred width settings are shown in the last image.)

There's an easy fix to just a few minor misaligned spots: make the dominoes concerned slightly narrower (or thinner). See image: One of the mortises on one of the legs refused to budge, so I made one of the tenons sightly thinner with sandpaper to bring everything in line. (The reason might be due to wood movement on the long apron rather than the mortising, but the reason wasn't important as long as the fix worked.)

 

[Christophl]

First of all, I really want to thank you Chuck for taking the time to write that long response. I really appreciate the help. I spent the afternoon trying to plane this long piece after I put it on a sled with shims. Despite that, we did not get the bow out of the word. I shimed the hell out of it so I don’t know why. So I decided to cut the board into two pieces for two smaller tables.  However, this project will be the same except the table will only be 45 inches wide instead of the 6 feet. 

The practice board that I tried I actually used the tight setting on the first and last domino, with loose in between them. I will try your suggestion of using only one with the tight setting.  And I did read the manual, several times lol

Your pictures are immensely helpful! As well as your suggestion of the sanding of the actual domino, that is really good to know!
Thank you again so much for the help Chuck!
Chris