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Thread: Need help with a box joint jig

  1. #1

    Need help with a box joint jig

    I just finished building a box joint jig using Ed Stiles plans https://www.youtube.com/watch?v=JYxDXHGRRrk

    I have a brand new Oshlun box joint blade set.

    The jig is great but the joints are way too loose. The slots are exactly 1/4 " but the pins are 15/64. which is 1/64 too small.

    Does anyone have any suggestion what is creating this??

    And how can I fix it.

    Thanks in advance.

  2. #2
    Join Date
    Dec 2009
    Location
    Newnan, GA
    Posts
    493
    After watching the video, I wondered if you're pushing the jig forward toward one side and then pulling it back toward the other side. He said that could make several thousandths difference in the way the joint fits.
    "When the horse is dead, GET OFF."

  3. #3
    Quote Originally Posted by Joe Kieve View Post
    After watching the video, I wondered if you're pushing the jig forward toward one side and then pulling it back toward the other side. He said that could make several thousandths difference in the way the joint fits.
    Especially if there is any play in the rails.

    BTW, If you believe William Ng, which I do, then you want between 5 and 6 thousandths of difference between the pins and the slots. A clearance of 1/64" is about 0.010" too much, but zero is too tight.

    I am no expert so take this for what it is worth.

  4. #4
    I built this jig: http://www.popularwoodworking.com/pr...saw-box-joints

    It uses a simple way to allow for zeroing in on tightness of joints, that once set up, won't wander. Only thing I found was I had to start with 4 or 5 slips of paper between the stops to get the range I needed, but I may have been using very thin paper.

  5. #5
    How are you measuring your slots and pins?

    How much side play is there in your sled?

    When you crank the carriage to one side or the other does the handle always stop in exactly the same position?

    Is your blade aligned precisely with the miter joints?
    Lee Schierer - McKean, PA

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Contribute

  6. #6

    I think I figured it out

    Quote Originally Posted by Lee Schierer View Post
    How are you measuring your slots and pins?

    How much side play is there in your sled?

    When you crank the carriage to one side or the other does the handle always stop in exactly the same position?

    Is your blade aligned precisely with the miter joints?
    I hope this displays properly. I found more sled side play than i thought I had. Replaced the runners which eliminated the side play. That did not fix the issue. I then noticed a small amount if play in the the threaded rod. I eliminated the play which tightened the joint up.

    Thanks for all the suggestions. They helped get my head back from major frustration that the jig was not working after all the work to build it.

    Thanks again

  7. #7
    Is it possible that your blade is not exactly a multiple of 1/16"to match the screw thread pitch. When you fit the blade edge to the work piece, that side of the joint will always be correct but if your blade is, say 0.129 instead of 0.125, the other side will always be be cut 0.004 wider. After calling the manufacturer of a new 1/8" blade I bought for my version of the jig, they said that the blades are deliberately ground several thousands over to allow for several future sharpenings. The new blade did measure at 0.129 with digital calipers and I went through some older ones to find one that was 0.125 and sharp enough to cut these joints.

    Slop in the runners will ruin any such setup though.

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