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Thread: Half dovetail dado joint

  1. #1
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    Half dovetail dado joint

    I need some advice on my desk on frame construction with hand tools. The writing desk surface is joined to the upper sides of the desk. I have a plan that uses a dado joint to connect the horizontal writing surface to the vertical sides. ( Just like a shelf on a bookcase ). The other plan has a half dovetail dado joint which looks nicer and is mechanically stronger. My concern is that the writing surface is 17 inches deep, and I do not recall sawing out a half dovetail joint this long. I have done tapered sliding dovetails perhaps 9 or 10 inches, but 17 inches seems daunting. I have crosscut backsaws of 20 inches and even 25 from miter box. Do I use this to saw the dovetail profile on the ends of the board? How do I get the matching housing in something this long? Ideas? ( Boy, the idea of a dado just seems easier ).highlighted half dovetail dado.jpgdesk plans.jpgdesk on frame.jpg
    Last edited by Mark Rainey; 03-11-2019 at 7:43 PM.

  2. #2
    I've been working with tapered sliding DTs lately and for the DT profile on the end of the board, I'd make a shoulder cut on the face of the board down to the taper line, remove the bulk of the waste with a chisel, maybe with an angled paring guide, and make the DT by using a side rabbet plane with an angled wedge on the depth stop, like this:

    IMG_1696.JPG

    The rabbet plane works surprisingly well: I used a 1:6 (9.5º) angle.

    I first saw the angled side rabbet plane idea a few years ago in FWW, and I believe Derek Cohen's website has a tutorial on this.
    HNT Gordon also has a youtube video on the tapered sliding DT using a very nice angled side rabbet plane.

  3. #3
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    Maybe run the 1/2 dovetail in a couple inches..then go with a dado the rest of the way?

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    Quote Originally Posted by Phil Gaudio View Post
    I've been working with tapered sliding DTs lately and for the DT profile on the end of the board, I'd make a shoulder cut on the face of the board down to the taper line, remove the bulk of the waste with a chisel, maybe with an angled paring guide, and make the DT by using a side rabbet plane with an angled wedge on the depth stop, like this:

    IMG_1696.JPG

    The rabbet plane works surprisingly well: I used a 1:6 (9.5º) angle.

    I first saw the angled side rabbet plane idea a few years ago in FWW, and I believe Derek Cohen's website has a tutorial on this.
    HNT Gordon also has a youtube video on the tapered sliding DT using a very nice angled side rabbet plane.
    Phil, thanks for the info. I will explore this.

  5. #5
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    Quote Originally Posted by steven c newman View Post
    Maybe run the 1/2 dovetail in a couple inches..then go with a dado the rest of the way?
    Steve, that might be an easy option. Let me think about that. Have you done this joint in the past?

  6. #6
    I like to use a joint that was common in mid 18th century: Run a dado about 1/8 deep and as wide as the writing surface is thick, say 1/8 X 7/8 for the whole width of your side. Then for the first two inches at the front, make a full dovetail socket out beyond the dado (farther into the side). Actually make the dovetails on the writing surface first, then slide the dado portion into the dado to mark the dovetail on the case side. saw and chisel the socket.

    This leaves most of the case side with almost full thickness, but with the dovetail to hold things together at the front. The full dovetail is a bit stronger and a lot more handsome than the half tail.

  7. #7
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    Quote Originally Posted by Warren Mickley View Post
    I like to use a joint that was common in mid 18th century: Run a dado about 1/8 deep and as wide as the writing surface is thick, say 1/8 X 7/8 for the whole width of your side. Then for the first two inches at the front, make a full dovetail socket out beyond the dado (farther into the side). Actually make the dovetails on the writing surface first, then slide the dado portion into the dado to mark the dovetail on the case side. saw and chisel the socket.

    This leaves most of the case side with almost full thickness, but with the dovetail to hold things together at the front. The full dovetail is a bit stronger and a lot more handsome than the half tail.
    Thanks for your advice Warren. I recall seeing a picture of that method.

  8. #8
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    Thanks for the idea Warren. Makes sense and should be less daunting than a 17" long half or full sliding dovetail. I have something similar to do for approx. 14"-15" long on my current project and have been wondering about expansion/contraction and fixing the shelf in place.
    Last edited by David Eisenhauer; 03-11-2019 at 10:11 PM.
    David

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    Would it be possible to make a dovetail at the back smaller than the dado with a dovetail larger than the dado at the front? (this could be turned around the other way.) Then the small dovetail could be slid through the dado and lock at one end as the larger dovetail slides in to lock in its socket.

    It would work like a tapered dovetail without all the fuss involved in tapering.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  10. #10
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    I’ve done this exactly twice (actually 4 times, 4 sides). The first time I did it full length and made the error of letting it sit for 2 weeks before assembly. I finally got both ends together by clamping cauls to the sides to keep them very straight to assemble. The next time I did the dado and short dovetail on the front and made a short dovetail key for the back and just put glue on the side panel of the key. Both have stayed together for years now. I would not go full length unless I was going to assemble fresh off the press so to speak. The short tail and the key were far less stressful at assembly time.
    Jim

  11. #11
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    Hi Mark

    There are a couple of factors that concern me about this construction. In the main I am in agreement with the suggestion made by Warren. That is what I have done before.

    The first issue is the sliding half dovetail. I would not place this where it will be visible. A two-sided dovetail is more appealing. Nevertheless the half dovetail has a place, which is at the rear of a cabinet (where it is not seen).

    The second issue is that the one in the photo is upside down in my way of doing this. The flat side should be on top. The dovetail needs to face down where it will wedge tightly and create a strong joint.

    Here is an example of placing the sliding dovetail at the ends only. To do this, the drawer blades are made from three sections: front and read cross sections, which are connected by mortice-and-tenoned rails ...

    This example is a little different insofar as the sides of the cabinet are a frame-and-panel, and not coplanar as with a solid panel ...





    It is OK to go parallel with short sliding dovetails ...







    Regards from Perth

    Derek

  12. #12
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    Interesting Derek - I agree that a half dovetail should be facing down - it might give better wedging action especially when weighted. Thanks for your thoughts.

  13. #13
    What do the dotted lines mean in your drawing?

    More specifically, what does it mean in the area you circled?


    Also, how close is the bottom edge of the panel to the half dovetail on the bottom of the desk?

  14. #14
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    Quote Originally Posted by Kevin Hampshire View Post
    What do the dotted lines mean in your drawing?

    More specifically, what does it mean in the area you circled?


    Also, how close is the bottom edge of the panel to the half dovetail on the bottom of the desk?
    Kevin, I believe this is an orthographic drawing, and the dotted lines are lines that you cannot see on the surface, but are there if you could see through the outside. I am not good at reading them, and I am not sure they are done quite right, but I am using them as best I can and am looking at other plans as well.

  15. #15
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    I couldn’t see your photos first go round. Your drawing does show a short dovetail with just a dado behind. That is what the dashed line indicates. That would be more typical than a full length sliding dovetail.
    Jim

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