Dadoes provide an excellent way to join cabinet sides to shelves, but in order for the joint to be strong the dado cut needs to be right. There are two common conventions for determining the depth of a dado cut, and we’ll explain them here.
Why a dado?
Dadoes are significantly stronger than a butt joint, thanks to way a dado completely houses the mating piece. Not only do you get a mechanical advantage between the two pieces, you also increase the glue area, a lot, making for a very strong joint that works great for cabinets, and boxes in general.
The table saw, paired with a dado head, is one of the easiest ways to cut accurate dadoes. There are both 6” and 8” dado heads on the market. You need a little background information to determine which size of dado head is right for you, your shop, and your table saw.
More about dadoes
When you’re ready to cut dadoes you need to know more than simply how deep to make them. You need to understand how to set up a stackable dado head, when to use dado shims, and how to determine if you’re getting the correct fit. No problem. WoodWorkers Guild of America has a great tutorial on cutting dadoes.
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Would be interesting to also give in mm. The USA is the only country using inches. It’s a good learning curve for Americans when also using mm ‘s
Part of the case for a half-deep dado is that it provides extra gluing area. There is no face-to-face gluing area in a dado joint so the extra gluing area is not of any use. If it were why not make the dado three-quarters deep?
There is some incremental benefit in the additional gluing area, but probably the bigger benefit is in the larger physical shelf, or the lower portion of the data that is extended in a deeper dado. But the case against making your dados 3/4 deep is that you begin to weaken the sidewall of the carcase if you go too far with it. All that said, I normally just go 1/4″ deep with most cabinetry dados, and I’ve never had one fail. A 1/4″ dado provides a lot more strength and support than it might seem.