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  1. #1
    Join Date
    Feb 2011
    Location
    Bristol Va
    Posts
    191

    Default How to make finger joints with Dado

    Ok i've looked thru here and found a few things but I am not following the directions on how to make a jig to us. I want to make finger joints with a dado blade for boxes. can someone give me detailed directions on how to make the jig board and how it works? Thanks

  2. #2
    Join Date
    Jul 2011
    Location
    Evansville, IN
    Posts
    2,505

    Default Re: How to make finger joints with Dado

    It's posted elsewhere, but I'll do a quite repeat.

    The jig is just a board screwed to the cross slide to hold the pieces you are cutting in the correct alignment.

    Here's how to do it.

    Set your dado up to the width you want. I use the full set plus a 0.010" shim as that will prevent a thin sliver at the bottom of deeps. You can use whatever width you want, but set it wide enough to get a nail into each finger without splitting them.

    Clamp a board about 15" long to the cross slide so that it overlaps the blade by at least 6". Set your blade depth to cut 3/4" deep and make a clean cut through the board. Measure the width of the slot you just cut, and cut a short length of 3/4" stock the exact same width. Trim to about 2" long, then unclamp the board from the cross slide and glue the piece you just cut into the slot so that an inch or so projects toward the blade. This makes the index pin for cutting correctly spaced fingers.

    Now comes the tricky part. Set the board back onto the cross slide and set it so the index pin is EXACTLY the width of your index finger from the blade. What you want is to cut a board held against that index finger so that the width of the "finger" on the board is almost exactly the same width as the slot you cut with the dado. Cut some scrap and check fit between two pieces. If they don't fit together with some friction, adjust the location of the board on the cross-slide to get them to fit well, then screw the board to the cross-slide.

    This is your jig. To use it, decide which side (long or short) you want to have a finger on the top edge. I like to put the finger on the long side and cut away the short side with the dado in it as this allows me to avoid any complicated cutting to get the dado to fit against a short finger. Cut all the fingers in the long board by putting it vertically against the jig with the top edge held against the side of the index finger. Cut a dado, then lift the board and set it down with the dado over the index finger. If you have things set up right, it will slip down with some friction, but seat against the top of the saw. If it's too tight, check alignment (more on that in a bit) or add a shim to make the dado set a bit wider.

    With the board over the index finger, cut another dado, lift off the board, set it on the index finger with the dado you just cut, and repeat until you have them all cut on one end. Flip the board over and cut the other side, remembering to use the SAME edge for the top finger -- I've ruined a few boards by rotating rather than flipping so that I got a top edge on both sides.

    To cut the matching board, you can either use a spacer between the index finger and the board that will have a dado on the top edge, or do what I do -- put one of the boards with the finger on the top edge over the index finger "backwards" so that the top finger is on the blade side of the index finger. I get better results this way.

    If you get it set up just right, the joints will fit together tightly enough you have to push to get them seated. You don't want them so tight you have to drive the boards together, nor do you want them to be loose and sloppy. If the fingers don't line up with the spaces all the way down the board, you have the space between index finger and blade wrong, or you have set the blade up differently than you did when you made the jig if you are using it later.

    Things to watch out for:

    You MUST have the blade perfectly perpendicular to the table, and the cross slide must be EXACTLY perpendicular to the blade. The blade must also be perfectly parallel to the cross-slide slots. Very minor deviations will result in joints that either require driving together or will make "racked" boxes that you will have to wrestle flat, neither of which is particularly desirable. Use a good square, not a cheap one or one that has been dropped or otherwise abused. You may have to square the table to the blade if you have not done so.

    Watch for sawdust on the table getting between your board and the index finger on the first cut, or getting under the board. You will get offset joints in the first case and shallow dados in the second, again not something you want.

    Depending on the grind of your dado set, you may have to cut and test to get the depth right. I have one ground to leave "glue grooves" on the sides, which is a huge pain. I don't want a gaping hole in the corners, I want them flat and square, but that will have to wait until I get them sharpened. I recommend cutting a test joint and adjusting to get the correct depth. You can record that setting on the gauge if you have one so you can repeat it, but I've got an ancient Delta tilt-top saw and the pointer for the scale is long gone, to say nothing of me being to old to stand on my head with a flashlight to see the damned thing.

    This is all harder to describe than to do, don't be afraid of it. Do watch that you keep your fingers well away from the saw blade -- I use 6" scrap to make the jig, you want to have it high enough you can't reach blade height while holding the boards. You will also need hearing protection, the noise that dado set makes while cutting end grain on a 20" board is incredible. Won't take but a few to damage your ears.

    Peter

  3. #3
    Join Date
    Nov 2009
    Location
    North Andover, MA
    Posts
    44

    Default Re: How to make finger joints with Dado

    I think you will find them easier if you search for a "box joint" jig.

    there is a good one similar to the one I use at http://woodworking.about.com/od/wood...oxJointJig.htm

  4. #4
    Join Date
    Jan 2013
    Location
    Midland, MI
    Posts
    586

    Default Re: How to make finger joints with Dado

    i made a quickie jig just claming "rails" parallel to the cut direction of a table saw. my table saw arbor would only accomodate a 3/8" stack of dado blades, but i tried it anwyays. it worked well enough, but i decided that I was a lot better off just running rabbet joints. with glue and staples, they seem plenty strong enough...especially considering that thei hive wont see any strange loading scenarios unless the keeper is man handling the box.

    The only reason i wanted to do the box joint is for aesthetics on staines and clear coated boxes. The added strength is a bonus, but with my set-up, not worth the time and effort. If i could have stacked 3/4" on the arbor, it would be a different story.

  5. #5
    Join Date
    Nov 2011
    Location
    Rader, Greene County, Tennessee, USA
    Posts
    6,335

    Default Re: How to make finger joints with Dado

    Here is the Beesource document on a box joint jig, with drawings:
    http://www.beesource.com/files/boxjoint.pdf
    Graham
    --- Practical reality trumps philosophy!

  6. #6
    Join Date
    Jan 2013
    Location
    Midland, MI
    Posts
    586

    Default Re: How to make finger joints with Dado

    i wish i would have seen that before i started on my set-up. although mine worked, ths beesource document shows a nice, simple way to do it. mine was not this nice

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