Domino 500 strong enough for bench/settle rails instead of tradition M&T?

[blairkd]

I am in the process of making a mission style settle/bench for outdoor use. The sides will have the traditional through mortise and tenon joinery, but I am thinking about using dominos for the rails that would join the sides together to form the supports for the seat and back.

I have the domino 500, so the maximum domino would be the 10mm x 50mm. I’ll need to order the outdoor dominos (Sipo ones) if I go this route.

The rails will be 5 1/2” wide by 75” long and 1 1/2” thick. Given the width and thickness, I can probably get 4-6 dominos (depending on which size dominos I ultimately use) instead of a traditional mortise.

If I have 3 adult males weighing 200 lbs plus sitting on the bench (enjoying a beverage or two) at the same time, that would be a maximum weight of maybe 650-700 lbs…can the dominos handle that much weight?

Thanks,
Kevin

 

[roblg3]

Yes.  Sipo is very hardy.  If you are used to M&T joinery you should know this is just the same except it's a loose tenon and the regular "suggestions" 1/3 max  apply.  You didn't mention which species your materials will be, but I expect it won't be as dense as the sipo?

 

[blairkd]

Thanks for the help!!

All of the material is pine. Some of this may change as I get further into the design, but: the posts that will form the sides are 3 1/2" square, all of the side rails and the cross rails will be 1 1/2" thick, bottom rails all around will be 5 1/2" wide, slats will be 3/4" thick...a little bigger/heavier duty than a standard mission style settle.

I'll use the domino for all of the slats that are typical for this kind of design in the sides and back rest, but those won't be taking the same sort of stress from weight as the corners of the long rails as they intersect the sides/posts (hope this all makes sense, a picture would be easier, but think of any couch, bench, chair design and you'll see what I mean by the sides and the joining longer rails).

As Jorg on lumber jocks noted: 3 adults weighing about 200 each equal 600 lbs, thus each of the corners (assuming even weight distribution) would have about 150 lbs of downward force placed on them. This should result in the dominos having a shearing (see Matthias Wandel's videos testing joint strength) force exerted on them. This is pretty much the maximum forces to which they should be subjected.

It seems like 4-6 dominos should be able to handle these stressors, but I cannot find anyone that knows for sure.

If I can use the dominos, I can reduce the M&T joints I need to make on the 2 settle/benches needed to as few as 8. If I need for structural/strength purposes to use M&T joinery at all of the corners, I'm around 28 M&T joints that I needed to make.

The dominos would make the project a lot faster and easier and I can concentrate on the "show" M&T joints. Which would be great, but I don't want some guest suddenly falling as the bench gives way.... [scared]

 

[HMR]

I've done numerous benches similar to your dimensions in various species of wood.  I use 2, 10x50mm dominoes per rail.  I use beech dominoes for indoor benches and Sipo for outdoor.  Titebond III is my glue of choice.  FWIW- A couple of my benches are at a Jiujitsu school and take an unusual amount of abuse.  It's normal to see 5 guys squeezed onto the benches after a class and the benches get hit and knocked over often.  Haven't had any issues with the strength of the joints.

 

[Wagon Willie]

I think that the Dominos will work fine in shear, but racking may be more of a consideration, depending on your design.  If you use a stretcher or some other form of triangulation then I would think the bench will be fine.  That said the Domino 700 was designed for this kind of joinery.  I also concur with the use of Titebond III if you are going with a clear finish, but epoxy would be even better if you plan on painting the bench.  Also, if you pre-seal the pine with some Seal Coat shellac before glue up then glue clean up is a breeze.  If you plan on painting the bench then this step isn't necessary.

I don't understand the use of Sipo, frankly, in this application.  Yes it will be very hardy, but the pine will fail quickly should water sit inside any of the joints.  The bench will then fail, but the tenons will still be in great shape!  An epoxied joint should be more durable, especially in Ponderosa pine.  If your are building with longleaf pine that has be pressure treated then the Sipo makes more sense.

 

[Birdhunter]

My outdoor benches were Ipe with #10 Sipo tenons. I would worry about pine for outdoor usage and any smaller tenons than #10s.

 

[roblg3]

1 1/2" is ~38mm  1/3 of 38=~12  so a 12mm domino is the max 10 sounds acceptable to me.  sipo(african mahogany) janka hardness 1180. depending on what species, pine wood is about 600.  you need roughly half as large of a sipo tenon as you would a pine tenon to achieve the same sheer.  I'm not an engineer, and hopefully one could say...but, this is how I figure things out for myself.  Does anyone see flaws in my logic? 

 

[Rob-GB]

This stool is made with one 10x50 domino in each joint and titebond 2 glue, timber is Douglas Fir/BC pine, I weigh 160 lbs so a lightweight but all the joints are in an angled shear, timber sections are 28x55mm(1 1/8"x2 3/16"). If anything goes wrong I reckon the pine will fail first.

I had some rather larger/heavier guys park their backsides on it two days after I made it and not a creak or crack in a joint to be observed.

Go for it but try to keep as close to the formula for normal tenons as possible within reason, as roblg3 mentioned earlier, .... someone posted a PDF about mortice and tenons a while back... [scratch chin]

Rob.

 

[blairkd]

Thanks everyone! I am now confident I can design the benches making use of the #10 50mm dominos.

Rob-GB's stool suggests that the dominos are more than strong enough as those angles have to be taking forces equal too or greater than the ones these benches will need to tolerate. I am now wondering if i need the center legs/support and whether I need to go with the sipo dominos.

The plan is to use outdoor stain for the benches, hence the use of the pine; something that should take the stain well and help them to last a good number of years. I did think of pressure treated lumber, but my understanding is that it never looks right (good?) when stained and my wife prefers not to paint them...I did consider cedar but selected the pine for overall look, costs, etc.

Definately titebond III or epoxy designed for outdoor use will be used.