Domino sizing; rule of thumb for selecting size?

[Michael Drew]

I'm still figuring out all the different applications for dominos. Current project is a couple cherry cabinets with 1.5" square corner post that I would have traditionally used M&T joinery with the horizontal pieces. I used dominos this time. I ended up using 8X50's, one per connection, and I think they seem snug enough. I went with this size after holding a few up against the boards and it looked to be big enough. I'm wondering though, is there a more, eh - scientific or educated way to make these determinations?

[Paul F Franklin]

I usually pick one that is about 1/3 the thickness of the thinnest piece in the joint, or a little thicker, and I use the longest domino (within reason) that fits in the pieces to be joined. In general, I try to leave 1/4" of "meat", minimum, all around the dominoes.

But I often go smaller/shorter when the joint will not take a lot of stress.

On a corner post of smaller size, the mortises might intersect; in that case I usually just go shorter on one side. You can also miter the ends of the dominoes for clearance when they intersect right at the ends.

[Jason Lester]

I do the same as Paul. I'll occasionally double up for a really thick joint, still following the 1/3 rule between them.

[Michael Drew]

Thanks for the input fellas.