The true strength of a domino...

[bkaimwood]

 So I'm wondering about the true strength of a domino… More or less.  It's a loaded question, so here are the details and the scenario. I have a festool domino, the big one.  I've used it a lot, mostly for doing slab table tops, breadboard ends, and some and grain joining, where I take to book matched slabs, and join them in opposing directions against the end grain.  It works great for breadboard ends because of the speed… You can bang out a set of breadboard ends on a table in 20 minutes instead of over two hours. When handling large material that tends to have some imperfections, it really helps out with slab alignment and getting things right working alone... it's like a second hand to hold things in place. For the end grain book matches I mentioned, they all are for stationary use… Wall art, headboards, and the such.
      Getting to the meat and potatoes, I am wondering about the true strength of a mitered end grain joint, joined using dominoes.  I am speaking of waterfall table applications. We all know that end grain cannot be glued... It just doesn't work. I have used west system epoxy in some end grain applications with the 404 thickener,  with mixed feelings… I've done them by the book, going through wetting and re-wetting, making sure that the end grain gets good saturation, while still having the proper amount of bonding material left once it is all absorbed.  I don't know what it is, but I'm just still not comfortable with it.  I have some customers that are looking for some waterfall tables, so I'm looking for a small coffee tables, others looking for large freestanding kitchen islands.  I've seen a lot of this type of thing on the Internet, and have seen no exposed joinery… I have done the typical searches online, and most places give you ideas on how to do it, while most telling you what a cakewalk it will be if you have a domino. Well, I have one,  but I am not convinced about the cakewalk… Maybe about the ease of use, alignment, and getting the thing together. It's the strength and long-term durability that I question.  Not wanting to count on anything actually in the end grain holding it together like a glue or epoxy, the domino is essentially the only thing holding it together.  Is that thing and that method of joinery really strong enough to hold that tight seam together through every day use overtime? I find it hard to believe. Maybe on a lightly used, ornamental, small coffee table… But on a 3 foot wide, 8 foot long kitchen island that is 30 inches off the ground?  I don't think so. I know there are plenty of forum  Friends and members with a domino, and also know there are plenty of you fellas who have done waterfall style projects. Your opinions and input would really be appreciated. Thank you!

[ljohnsaw]

 

[Dan_Shade]

A 45° miter has long grain and end grain....

A loose tennon adds strength and makes assembly easier too

[Larry]

A recent article in FWW covered some new approaches for that joint using metal angles.

[grouch]

How about splines for your miter joint? Make a fingerboard box, quarter it, you have 4 fingerboard splines to put into the joint.

[woodworker9]

After a pretty in depth study on FWW, as stated, it was determined that the strength of a joint put together with domino's is, well, not so great.  You can easily look up that article and extrapolate whatever you like from it.

If you want the table to last, especially in a waterfall style, there are better options.

I build tables like this with full, exposed, hand cut dovetails that are attractive looking, at least to most of my customers.  Not everybody wants that look.  There are also mitered dovetails, that are a little bit trickier to lay out.  You can google or YouTube the heck out of that to find out if it's for you.

You can also install a full length spline to strengthen the joint.  I've done a few of these, and they hold up.  When I miter cabinet doors, I always use a full spline for strength, and have never had one fail.  A table is a different animal, since it will be carrying more wait.  A hardwood spline that is epoxied in is a better choice than a domino.

[ljohnsaw]

So I was curious and Googled the Festool Domino and it popped up on Amazon.  Pretty cool tool, like the whole Festool line.  But, at $990 I would expect it to do all the work for me   I kind of feel that, like normal biscuit joinery, they are great for aligning but, IMO, I wouldn't rely on them for strength.

[grouch]

Apologies for being confusing. The term "fingerjoint" used to be synonymous with "box joint" but seems now to only refer to those joints used to join short scraps end-to-end into long pieces to manufacture molding and such. So, let me try this again...

Make a square wooden tube using box joints. Quarter it and you have 4 splines to strengthen a miter joint.

On another note, I wasn't sure what a "waterfall table" is so I googled it. Man there are lots of lacerations waiting to happen in the images I found. Sharp corners and edges, to me, are the mark of assembly line mass production furniture. Toddlers, running kids, adult shins and heads are given total disregard in favor of speed of machining and profit. (Years ago I worked at a small cherry furniture factory. One of the guys there called me "router fingers" because I made those edges friendly). I love it when somebody spontaneously reaches out to rub their hand over something I've made; it's the best compliment. Ok, rant over.

[bkaimwood]

 Thank you for the input fellas. Seems my own personal experience, concerns, opinions, and such about the whole deal are justified  and, more or less, fall in line with what you guys are  saying and feeling as well. Splines alone will not be any stronger than a domino, in my opinion. Epoxied splines will be stronger than a domino alone, I agree. And epoxied domino will probably be the strongest of all, comparing similar methods.  Woodworker9... I am familiar with the style dovetails that you are using… It's unique, great looking, and a strong design. It is not what this particular client is looking for though. I would consider in place of the style that you are using doing blind dovetails, which are probably comparable and strength, but not as strong. And as you mentioned, it's fine for small stuff, but not for heavyweight tables.  I had already told my client that they would have to pick one of three designs and order for me to build and guarantee what we were doing. The first option was a trestle or stretcher piece tucked up tight underneath... for example, on a good-sized, freestanding island, a 2 x 6.  The second option was to put a pair of triangles up top in the corners tight, kind of like corbels.  It makes a huge difference having something up in the corner to reinforce and make a square. The last option, which is the one they chose, is having a piece of angle iron routed into the corner, and painted a similar color to minimize  it's noticeability.  And of course, it can't be one long piece… That will not allow for expansion and contraction… It will have to be several pieces, one on each board… So in other words, if it is a four board glue up, each side will have four pieces of angle iron routed in underneath.  I don't think I have anything to worry about then.  But I would have preferred to do the 2 x 6. I think it would look better, and be plenty strong. But I think my client is hung up on the floating look and not seeing anything underneath.  Someone had previously mentioned doing something with angle iron here, and I think it's a great idea. Thanks again for all your input.

[ljohnsaw]

And of course, it can't be one long piece… That will not allow for expansion and contraction… It will have to be several pieces, one on each board… So in other words, if it is a four board glue up, each side will have four pieces of angle iron routed in underneath.

Why not one long one with oval grooves much like what is done with wood cleats?  If I were to do that, I'd have the table finished and waxed (wax the iron, too) and then it could slide if it wants.  How thick with the top & legs be and what will the dimensions of the steel be?

[bkaimwood]

Good question, ljohnsaw. I have done similar things on panels with wood...we'll call them battons. I make an elongated slot in the batton, the route a recessed, countersunk face the width of the flat washer I will used, also elongated. When I attach the batton, I "zero" out the clearance when tightening the attachment bolt...or tighten it, and back off 1/4 turn, or whatever...you get the idea....allow for sliding for expansion and contraction. Unfortunately, this forgiveness that allows sliding would be enough to at least break the invisible finished seam at the mitered corner. Although it may not be enough for any significant separation, it would be enough to likely separate the finish or make the appearance of a small crack. Maybe your average Joe wouldn't see it, but I would....we all have our problems .....

[Just Me]

Use the Domino to cut the longest mortise you can and then make some steel reinforcements, bed them in epoxy?

I have a domino as well and am not really impressed, seldom use it.

[ljohnsaw]

Unfortunately, this forgiveness that allows sliding would be enough to at least break the invisible finished seam at the mitered corner.

Maybe I'm missing something here.  Are you making a waterfall table/counter?  So all the grain is in the same direction - to the end, over the edge and down.  You will make a miter joint that will be glued.  You may or may not put in biscuits or dominos for alignment and minimal strength.  It would have the routed recess on the inside corner to accept the angle iron brace.  All surfaces would be finished and then the angle iron would be installed.  If the top expands (width-wise) so will the leg.  There should be no opening of the miter joint, the way I see it.

[bkaimwood]

Unfortunately, this forgiveness that allows sliding would be enough to at least break the invisible finished seam at the mitered corner.

Maybe I'm missing something here.  Are you making a waterfall table/counter?  So all the grain is in the same direction - to the end, over the edge and down.  You will make a miter joint that will be glued.  You may or may not put in biscuits or dominos for alignment and minimal strength.  It would have the routed recess on the inside corner to accept the angle iron brace.  All surfaces would be finished and then the angle iron would be installed.  If the top expands (width-wise) so will the leg.  There should be no opening of the miter joint, the way I see it.

     You explained the plan and design perfectly. I don't know that you are or are not missing anything, maybe just not weighing in how critical  this piece of angle will be, and exactly what it will be doing. One piece in question will be 3 foot wide, 8 foot long, 3 foot off the ground. That's a lot of leverage for a leg to have on a relatively small, end grain, mitered joint. The angle will not be there to help out or aid in the strength of the joint, in my opinion, it will be the backbone of strength for the legs. In other words, having the angle bolts just snugged and allowing for floating/expansion/contraction is not good enough. The fasteners will be substantial, and they will be TIGHT.
     I see it like this. Any wiggle room you leave to allow for expansion/contraction is the same amount of room you leave the joint to fracture. These pieces will be going to a land far far away and I'm not taking any chances.
     

[ljohnsaw]

OK, thanks.  I see your desire for multiple brackets.  So, if you make 4 brackets for each end, say 3 to 4 inches long, I would think you could put two bolts on each face and fully tighten them and not worry about expansion/contraction in that minimal area.  Do you plan to use something like 3"x3"x¼" angle?

[bkaimwood]

I hadn't nailed down an exact size, but that sounds about right...definitely 1/4" thick...2 bolts per, good and tight, and forget it...I'll be painting the angle ahead of time a similar color as the wood to help it blend in...

[Larry]

When the Crystal Bridges Museum of American Art opened in 05 I noticed these very attractive benches scattered throughout the museum.  They get pretty rough treatment from way overweight seniors to rambunctious kids.  No exposed hardware or fasteners.

 

 
At that time I was laminating lots of oak in the same manner as the benches but just for table tops.  It was a short jump to copy the museum benches.  My method is a steel angle iron “L” tendon.  The article I referenced earlier in FWW discusses several varieties of “L” tendons.  Probably better than the tendon I used in my benches.

[ScottAR]

I wonder if a dowel type joint using steel pins would work?  Stainless perhaps?

Just throwing it at the wall to see what sticks.

[Ianab]

The problem I see with steel angle iron is the wood movement. A bench like that is going to change in width slightly, but measurably, with the seasons. This might  be enough to break the glue bonds to a long steel reinforcement, and weaken the joint over time.

Now a series of angle iron pieces, like a 2" piece, 1" gap, all the way across? Now that should avoid the problem because the movement over 2" isn't enough to rip the glue apart.

Same idea with metal "tenons" or "dowels". Because the tenons are maybe 1" wide you can ignore that movement. The next one is 4" away, and has no effect.

Another one would be to use a chunky wooden spline. Cut a stopped 45deg slot in each piece, where the groove ends just short of the outside edge. Then the spline grain runs with the grain of the other pieces. Its a 12" x 1",
just it's only 3 " long. But all it's strength is holding the joint, and it moves in the same way as the rest of the wood.

If you wanted to, you could use a contrasting wood, and show the spline on the outside. The good old Maple bench with the walnut accents, or visa versa. Commonly used on jewellery boxes, but no reason it wouldn't scale up.