Domino Spacing - Not the Typical Question

[DanMcDan]

Posts I've seen do not address my question.

I am making an outfeed table with 1.5 x 3 1/8 inch ash. I am using the 700 to join with 14x100 dominos.  I can place one in the middle of the stretcher ends to connect to aprons, or I can place two, but will I have enough meat left to support the structure.  My head says 2 glued in dominos will be just as strong as the wood itself, but my OCD worries it will all come crashing down.

So, is one domino enough?  Or do I use two?

Thanks!

 

[MikeGE]

It's been a while since I used my 700, as I tend to use the 500 for most of my projects.  However, even then, I used it for alignment and assembly as opposed to a key structural component. 

I had to convert your ash measurements to metric, which is about 38 x 80mm, so I could visualize the application.  I tend to adhere to the one-third guidance when selecting a domino size.  In your case, I think a 14mm domino is too large for the stretcher thickness and would use two 10mm or 12mm dominos.

 

[rmhinden]

14mm dominos should be fine.  The 1/3 guidance is a good guideline, but in your case I think there will be plenty of wood on both sides (~ 1/2") of the domino. 

I suspect one would be strong enough, but if it reduces your concerns about strength, use two.

Bob

 

[smorgasbord]

The real question, IMO, isn't the thickness, but with width.
A 14mm domino mortise, cut on the tight setting, is about 27.5mm wide.
With an 80 mm stretcher width, the calculation for spacing is:
80-27.5-27.5=25mm
Split that 3 ways (top, bottom, middle spacing between them) and you get just over 8mm.
That's not enough.
Going to 12mm tenons saves you a bit:
80-25.5-25.5=29 / 3 = 9.7mm, but probably still not enough.

I'd consider doing a 12mm and then a 10mm, or a 14mm and a 8mm. The larger one holds the joint, the small second tenon resists twisting.