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Calculating wood length that use Half-blind Dovetails

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Forum topic by CanadaJeff posted 07-07-2009 09:00 PM 1351 views 0 times favorited 7 replies Add to Favorites Watch
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CanadaJeff

207 posts in 3076 days


07-07-2009 09:00 PM

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.


7 replies so far

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PurpLev

8523 posts in 3115 days


#1 posted 07-07-2009 09:06 PM

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.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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lew

11343 posts in 3221 days


#2 posted 07-07-2009 09:09 PM

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.

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

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CharlieM1958

16244 posts in 3684 days


#3 posted 07-07-2009 09:14 PM

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.

-- Charlie M. "Woodworking - patience = firewood"

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CanadaJeff

207 posts in 3076 days


#4 posted 07-07-2009 09:43 PM

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.

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CharlieM1958

16244 posts in 3684 days


#5 posted 07-07-2009 09:54 PM

I could maybe argue with reasons #1 or #2, but I can’t argue with #3. :-)

-- Charlie M. "Woodworking - patience = firewood"

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CanadaJeff

207 posts in 3076 days


#6 posted 07-07-2009 10:07 PM

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

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CanadaJeff

207 posts in 3076 days


#7 posted 07-08-2009 02:58 AM

It worked!

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

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