# depth of tongue and groove ??



## larry0846 (Feb 20, 2013)

how does one decide what depth to use -- i see using a 1/4" width on standard 3/4" boards -- do you always use a third of the stock width for groove width ? surely, 1/2" depth is stronger than 1/4" depth -- are there 'rules of thumb' to giude you driven by the application ? hard or soft wood ?

appreciate your experience and insights --


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## Hammer1 (Aug 1, 2010)

If you cut the T&G 1/4" thick by 1/2" deep, you will have some rather weak parts that are easily broken. You can go up to about 3/8" deep if making your own but you may have a lot of breakage if going much deeper. Not much difference between hard or softwood. A T&G joint, such as one might use for paneling, doesn't fit tightly all around and would require clamping the "ears" of the groove side tight to the tongue, clamping down, not together. That doesn't work well for most uses of a T&G joint, there can be exceptions.


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## woodnthings (Jan 24, 2009)

*I use the 1/3 rule*

A tongue and groove joint serves two functions, one is to align the 2 pieces and the second is to provide additional gluing surface, strengthening the joint. Making the tongue deeper than 1/3 the thickness does not serve any structural purpose. The weakest point is at the intersection of the tongue and it's piece of origin.

A glue line router bit will do the same thing:










http://www.thewoodwhisperer.com/articles/does-a-glue-line-bit-add-strength-to-a-joint/


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