Domino Strength Test

[Mini Me]

Conventional Mortise joints often get pinned or draw bored, Has anyone here done that with a Domino joint? A domino joint could be draw bored if the Domino was first glued into one mortise, pinned and glued then allowed to dry for a short time, a bit of mucking around and certainly long winded but it would increase the strength factor multiple times as would simply pinning it with a dowel.

I have as I stated earlier in this thread always seen the Domino as an alignment tool and I don't glue Dominos when using it that way but now I am beginning to see it as a bit of a hybrid when it is essential for high mechanical strength though I am yet to try it. By using the Domino to create the required width dimension of the mortise(s) using multiple cuts and the maximum depth the mortise would then be used as a template to make it deeper using a chisel in a few minutes and a loose tenon made to suit the mortise(s). The problem I see with using stock Dominos is that they don't utilise all the possible area that a conventional tenon does or can. Glue strength can never surpass mechanical strength and the loose tenon system that the Domino makes often falls short of the maximum glue area possible, a hybrid approach will overcome that issue but it would only be practical on bigger M&Ts. 

An interesting question might be, why did you buy your Domino and how did you intend to use it, as a loose tenon joint maker or an alignment tool?

 

[ChuckM]

Snip.
An interesting question might be, why did you buy your Domino and how did you intend to use it, as a loose tenon joint maker or an alignment tool?

90% or more for loose tenon joints, 5% or less for alignment, and 5% or less for other uses (such as for slot cutting, etc.) . In fact, I use dominoes in edge joining more for the sake of having fun with dominoing! Dominoes or biscuits are not necessary for panel joining.

 

[mrFinpgh]

Conventional Mortise joints often get pinned or draw bored, Has anyone here done that with a Domino joint? A domino joint could be draw bored if the Domino was first glued into one mortise, pinned and glued then allowed to dry for a short time, a bit of mucking around and certainly long winded but it would increase the strength factor multiple times as would simply pinning it with a dowel.

Chris Schwarz does this with his chair seats, pinning each domino joint on both sides.

Drawboring a loose tenon - it's an interesting idea, but like you say, you'd need to glue one mortise first.  I think I would not want to be in a situation where I needed to drawbore a domino for structural assurance, but I can see some appeal for avoiding a lot of clamping.

 

[luvmytoolz]

I bought it for both alignment and the added strength from more glue surface. And at the moment I'm working on a table top that I'll be fixing breadboard ends to using drawbored dominos to allow for movement.

 

[Packard]

I was not familiar with the term “drawbored” so I looked it up.  For the benefit of others not familiar with the term, I am showing a diagram I found.

It would appear that this is a technique usually used in mortise and tenon construction.  I did not see any mention in relationship to floating tenons.

It would seem to me, that you would have to not only glue one end of the tenon in place, but also cross pin it or it would remain weaker than the end that had a drawbored pin. 

I read an article years ago about replacing rivets on older bridges with nuts and bolts.

At first glance, the rivet would appear to be stronger than a bolt.  After all, a rivet going into a 1” diameter hole could have about a 0.970” diameter body.

A bolt going through that same hole would have to be nearer to 0.800” for the body and the balance to consist of the threads.

But the key differences were:

1.  A rivet had to be made from a soft, malleable grade of steel.
2.  A bolt could be made from high strength steel because it did not have to be peened over.

But the biggest difference was that when bolts were torqued down, the joined plates then generated a good deal of friction.  So for a bolted joint to fail, the shear would have to first overcome the friction between the joined plates and then it would have to shear the much tougher steel in the bolts.

So a joint under tension gains tensile strength by having the tenons cross pinned and further gains shear strength by generating face to face friction between the two pieces of wood being joined.

I will have to think about this.  I don’t usually see joint failures due to shear, where the tension on the joint would add the most strength.

And I don’t usually seen failures due to tensile strength.

Most of the failures I see are due to racking (bending of the joint components. 

There are exceptions.  Drawer fronts experience a great deal of tensile stress.  That is why the strongest joints are frequently used there (dovetails).

Chair joints usually occur due to racking which stresses (bends) the components beyond the “modulus of elasticity” (beyond their ability to return to the pre-stressed condition or shape.)

I am trying to figure where drawboring would add much over cross pinning.  I think it would in timber framing.  I’m not sure it would have much benefit in cabinet building or general wood working.

 

[MikeGE]

I am trying to figure where drawboring would add much over cross pinning.  I think it would in timber framing.  I’m not sure it would have much benefit in cabinet building or general wood working.

I used drawboring for M&T construction in situations where clamping was difficult because of the angle of the joined pieces or the span was longer than my clamps.  When I was younger, I helped build a timber frame barn and every M&T joint was held with a drawbored pin.  There wasn't any glue used on the joints, and as far as I know the barn is still standing.

 

[Michael Kellough]

I’ve always wanted to build a timber framed structure but never had the chance. Short of that I occasionally construct something without glue and use similar techniques to keep the assembly together. It’s fun to think through such basic mechanical constraints.

 

[luvmytoolz]

For breadboard ends drawboring is pretty essential as the center 1 or 2 dominos are glued fully at both ends, but the others are glued into a tight slot on the table side, with the other end in the breadboard being a loose fit to allow wood movement, so an elongated hole is made through the breadboard and domino to "pin" it so it pulls tight against the table, but can still move sideways as wood expands/contracts.

 

[Mini Me]

Thanks for the replies to my question, I have never seen this aspect discussed when it comes to Domino joint methods and for me cross pinninig would be sufficient as long as the dowel was not too large. Using a Domino to make a larger mortise has some appeal as it takes away a lot of the set up time via conventional measuring and marking and if the mortise is not deep enough a chisel will sort that out.

 

[luvmytoolz]

Thanks for the replies to my question, I have never seen this aspect discussed when it comes to Domino joint methods and for me cross pinninig would be sufficient as long as the dowel was not too large. Using a Domino to make a larger mortise has some appeal as it takes away a lot of the set up time via conventional measuring and marking and if the mortise is not deep enough a chisel will sort that out.

I plan on making some extra wide dominos when I get time (ha!) to suit the available existing width settings, so not long back I went through all the cutter sizes and did a test cut in each size/width, and came up with the following real world chart of the slot width measurements.

I'd imagine mine would be pretty much the same as the other models out there. Some have been rounded down a poofteenth to the nearest 0.5mm.

 

[ChuckM]

This fellow has reported something similar:http://web.hypersurf.com/~charlie2/DOMINO/DOMINO_TenonsMortiseWidth.html