Right Size Dominos for Joining 3/4" Stock at 90 Degrees?

[grbmds]

Just verifying that it's OK to use a 5X30mm Domino to joint 3/4" stock at 90 degrees? My concern is the depth that the Domino slot will go into the 3/4" thickness. I've taken measurements and it appears that there is about 4-5 mm to spare when comparing the 3/4" thick piece to the depth of the Domino slot. Is that enough remaining wood? It's quartersawn white oak.

To be safe I could use the 4mm Domino given it's a support for a bottom shelf on a nightstand, but would rather use a 5mm for strength.

I have attached 2 pictures showing the front and side views. It is the curved supports which I am attaching to the straight sides.

I am making a second table like this one (which was made about 6 years ago) and really don't remember what size Dominos I used, so just trying to be safe.

 

[Birdhunter]

My method on this type of joint is to have unequal mortises. I drill a short mortise on the thinner piece and a deeper mortise on the other side. The total is what is required for the tenon. For a 50mm tenon, one mortise at 10mm and one at 20mm instead of both at 25mms

 

[ChuckM]

For your 3/4" stock, a 15mm cutting depth is perfectly fine for the 5mm x 30mm tenons.

If so desired, you could even use 6mm x 40mm tenons, and set the cutting depths to 15mm (for 3/4" stock) and 25mm (for the curved supports).

Also remember that all tenons are actually 2mm shorter than their stated lengths. For example, a 10mm x 50mm tenon is only 48mm long.

 

[HandyDen]

I run a small cabinet shop, and I use 5mm dominoes exclusively to join 3/4 plywood at 90 degrees - all the fixed shelves, tops and bottoms are fixed to the sides with 5mm dominoes (in fact, I use that size so much I just bought another 1800 pack today).  I find the 5mm has plenty of strength using 1 domino every 12-18”.  And the 30mm length means I don’t have to change the depth when cutting the mortises in the cabinet sides.

 

[grbmds]

Thanks for both responses so far. I have done unequal mortises in the past. I was quite sure that the 5X30 would work and probably did that the last time I made this table for my daughter. It would have been too easy for her to want 2 to begin with. She insisted she would not need 2. If anything, this second one is a little bit better in technique than the first.

 

[smorgasbord]

5mm is pretty thin - same thickness as a biscuit.
34" stock is 19mm. The one-third rule says to use a 6mm biscuit.
I once posted asking why Festool doesn't make a 7mm biscuit, as I think that would be ideal in situations like this.

 

[Crazyraceguy]

I use far more 6mm Dominos than any other size, and would in this case too. Off-setting them as 15-25 rather than the usual 20-20 works out fine.
Two cautions go along with this. First is because of the off-set, you have to remain aware of what you are doing. Forgetting to change the depth stop will put a hole in the side of your carcass. This is the main reason that a lot of people use the 5 x 30. Both sides get the 15mm depth, so this is eliminated.
The other is about gluing. Take care to not over-glue the mortises in the sides. Over-filling can cause hydraulic lock which can split the wood, or force glue out through the end grain of your parts. This is especially apparent with porous wood like red oak.

 

[grbmds]

I also use 6mm Dominos more often than other sizes as indicated by the fact that my supply of 6mm is almost gone whereas I still have a lot of the other sizes. In this case the slots will be vertical and the side to side stress on the joint is minimal (see pictures on original post). The 5mm should work just fine. The depth of the slot in the table side support was my only concern.

 

[Crazyraceguy]

I also use 6mm Dominos more often than other sizes as indicated by the fact that my supply of 6mm is almost gone whereas I still have a lot of the other sizes. In this case the slots will be vertical and the side to side stress on the joint is minimal (see pictures on original post). The 5mm should work just fine. The depth of the slot in the table side support was my only concern.

I just opened a second bag (300) of the 5mm Dominos, in contrast to the 3 entire boxes of 6mm, after the initial bag (190) from the set in the Systainer. The boxes come with 1140 in the 6mm size.
I would imagine that this is far from the average user though, I'm in a big commercial cabinet shop. There are days when I use a hundred at a time, and that just since the move to the new building, just over 2 years. They are not all 90 degree joints though, a lot of them go to wall panel applications where a Lamello Zeta P2 Tenso clip holds them together.