# Calculating wood length that use Half-blind Dovetails



## CanadaJeff (Jul 8, 2008)

I'm going to be making a medicine cabinet that is recessed into the wall. I have a half-blind dovetail jig and decided I would like to use it to frame the medicine cabinet. The only issue is cutting the wood properly so that the end product is the precise size of the hole in the wall its going to fit into.

If I was going to use mitres measurign wouldnt be a problem because the end of the mitre would be the size of the hole, but with half-blind dovetails I have to compensate because two sides (that have the pins) because they fit into the other sides. Thus I need to take into account the thickness of the other two sides and the depth that the pins go in.

Right now I'm thinking the only way to get the right size would be to test cut some pieces, calculate the depth the pins go into the wood and the thickness of the recieving sides and figure out the length of wood I need to reach my desired length. Does this sound right? Does anyone know of another way to determine the length?

Any help is appreciated.


----------



## PurpLev (May 30, 2008)

it really depends on the thickness of your material, and the dovetail jig/bit you're using… so the only way I can see you'll get a perfect measurement is if you follow your own advice and make some test cuts, have a small joined corner, and take measurements off of that.


----------



## lew (Feb 13, 2008)

Most jigs create the half blind dovetail that is half the thickness of the side/end. So one set of pieces top/bottom or left/rite side will be the full length/width of the opening. The other set of pieces will be shorten by the thickness of you stock. If you have a 10w x 20h opening and 3/4" stock and the "pins" are on the side pieces then the top/bottom pieces will be 10" and the sides will be 19 1/4.


----------



## CharlieM1958 (Nov 7, 2006)

In my experience, Lew has it right. But if I were you, I'd make the test joints anyway just to be on the safe side.

Having said that, I'm wondering why you want to even bother with dovetails on something that will be recessed anyway.


----------



## CanadaJeff (Jul 8, 2008)

Charlie, three reasons for the use of the dovetails. 
The cabinet isn't entirely recessed, more semi-recessed, so there is some exposure. 
Secondly, I'm recessing it into a pre-existing hole that was isn't sloped so the cabinet is actually going to be paritally suspended. I figured that dovetails would be a strong joint to use and can hold up to the weight and potentailly not being pefectly flushed with the base. I would hate to put in the cabinet, load it up and have a mitre give because of the weight. 
Lastly, it gives me another chance to play around with dovetails and learn a few more things.


----------



## CharlieM1958 (Nov 7, 2006)

I could maybe argue with reasons #1 or #2, but I can't argue with #3.


----------



## CanadaJeff (Jul 8, 2008)

I agree Charlie, I really don't know if dovetails are appropriate, but im anxious to make them!
Cheers


----------



## CanadaJeff (Jul 8, 2008)

It worked!

Length to use = Desired Length - 2x the remaining depth after the pin is inserted


----------

