Domino sizes for imperial plywood

[rmhinden]

I am learning how to use my new XL 700, and like it a lot.  The Seneca Domi-Shim kit makes using imperial sized wood a lot easier.  I have a question about domino sizes. 

From what I can tell the conventional wisdom is that one should use a 4mm domino on 1/2" plywood and a 6mm domino on 3/4" plywood.  Holding the domino up to the plywood, it seems to me that 5mm and 8mm dominos will also work.  I have been using marine plywood that is very close to the actual 1/2" and 3/4" sizes.  Baltic birch is thinner, but even this appears to work with the 5mm and 8mm dominos.

Is there a downside to using these larger domino?  What are others experience?

I also note that sipo only goes down to 5mm.

Thanks in advance.

 

[PaulH99]

The rule of thumb with tenons is that they should be 1/3 of the thickness of the wood. In this case, true 3/4" plywood (19 mm) would use approximately a 6 mm tenon. You could go a little thicker or thinner without affecting it too much.

 

[leakyroof]

For Baltic Birch or something similar to it, I tend to err on using 5mm tenons , this way I don't 'telegraph' a swollen Domino tenon through to the surface of the plywood by using a too thick tenon. I think the quality of the Plywood matters for this, and it could be that I've run into bad batches or poor batches of Plywood that don't resist a 6mm tenon with 3/4" or undersized ply that well.
For Hardwood, I'm not that worried about it. Haven't seen a 6mm tenon cause issues as long as I'm center on my material with the mortise.

 

[PaulH99]

Yeah, [member=10952]leakyroof[/member] is right. Measure the thickness of your plywood with calipers so you have an accurate number. Multiply by 25.4 then divide by 3 and you should have the recommended tenon (domino) size to use.

 

[Stephen B]

https://www.facebook.com/festoolaustralia/videos/2056412977905651/

Where Sedge says 5X30mm.

 

[Birdhunter]

The 5mm tenons are my choice for 3/4” plywood. I find less glue is a lot better than glopping it on. Too much glue and the hydraulic pressure of forcing the tenon into the mortise can blow out the wood.

 

[koenbro]

I use 6mm dominos for 3/4” and 4mm for ½ “.

The DF500 is so precise that I use the nominal width on all mortises, don’t go one size (+3mm) up, yet still achieve perfect alignment.
The Domino is really a game-changer.

Sent from my iPad using Tapatalk

 

[sancho57]

I just figure like this, 1/2" is about 12mm, 3/4 is about 18 mm i use the tenons accordingly

Heres a tip, when I find a domino that works for a particular thickness , I write down the domino the domino settings somewhere for reference.

Please refer to this chart
http://www.rempros.com/dimensions/plywood_sizes.html

 

[guitarchitect]

not to be crass but everyone always trots out the 1/3rd rule... it's kinda irrelevant when we're talking about case goods. You can do M+T that are more or less than 1/3rd of the thickness of the material if you darn well please, it just won't be optimal. but most of the time it doesn't need to be optimal. You're essentially using the domino as an alignment aide with plywood (depending on the joint + loading conditions, of course). As long as it's not so thick that it leaves a single ply on either side, I would err on the smaller side because it leaves more plies intact.

I took someone else's advice and haven't looked back - use a 5x30 domino, everywhere. You never have to adjust the depth of the mortise, so you will NEVER have an "oh crap" moment where you either plow a mortise through the plywood's bottom face (25mm setting on 19mm plywood), nor will you end up with shallow mortises in the end of your plywood (like when you use 6x40's and you have to do a 15mm mortise on the ply face and a 25mm mortise on the ply end). Is it the mathematically strongest joint? No... but it doesn't really need to be.

 

[ChuckM]

I rarely use the DF on plywood, but this "5mm x 30mm tenons for ALL 3/4" plywood" makes good sense, as it reduces cutting blunders.

 

[skids]

the biggest reason not to use anything more than the 6mm is the length of the domino on anything larger throws off the cutting depth set up. would be too much stopping and going and adjusting settings to get it to work.

 

[PeterK]

For me, I find that in plywood the domino with glue tends to swell the plywood and it can take a day or more for that to shrink back as the glue dries properly. Have made a few sanding mistakes with swollen plywood. I have less chance of swelling with using the thinnest dominos. Yea I could be doing it wrong by using too much glue. I have not really noticed this problem in hardwood but have seen it in pine.

 

[Roseland]

For 3/4" ply I use 5mm, because they're only 30mm long, so I can set the depth of plunge to 15mm and be safe on both cuts.

The 6mm are 6mm x 40mm, so a 20mm plunge, and if you forget that with ply that's 18mm...

Andrew

 

[Bugsysiegals]

I just made my first cabinet yesterday and blew through the 19mm edge banding on one mortise.  I'm now seriously considering the 5x30 to avoid this from ever happening again ... thanks for sharing!

 

[ChuckM]

Also this: When mortising, develop the habit of starting with cutting all the shallower mortises first, before resetting the depth for the deeper ones (e.g. on the endgrain).

 

[Bugsysiegals]

Also this: When mortising, develop the habit of starting with cutting all the shallower mortises first, before resetting the depth for the deeper ones (e.g. on the endgrain).

Thanks, similarly since I use the extension wing for repeatable cuts rather than marking things, I’m moving A-Z for reference. For example, Back you Front, Bottom to Top, Left to Right.  Like anything it helps to have good order of operation and easy to remember routine to avoid mistakes. 

 

[Jiggy Joiner]

If it’s just boxes and workshop cabinets, or exhibition stands etc with 3/4” 18mm ply, I use 5mm dominos.
If the joint is structural like a bracket, or shelf that’s taking good weight, I’ll use 6mm.
Don’t be tempted to go too thick with a domino, more so in structural jobs, because you are then removing more material from around the domino, which can be a weak spot. I like the 1/3rd ratio, or slightly under, it seems to work well.