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box joint problem

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  • box joint problem

    What am I doing wrong???
    I took a stab at making my first box joints yesterday. From what I've read in the past, I expected that I'd have to tweak the jig one way or another to adjust for fingers too tight/loose or too short/long, but I'm having another problem. The fingers start off aligned at the top of the box (these are the first cuts I make), then they slip out of alignment as I work my way down the box. Why don't the fingers align? (I have my suspicions, but I'm not sure). Times like this I feel like an idiot!

  • #2
    Welcome to the "I feel like an idiot club". Most of us belong to this club. I think you have just discovered a phenomenon known as "cumulative error", which is fairly common with many box joint jigs. Think of it this way. If you are off on your spacing only .010, by the time you get to the end of your cuts, you could be off by as much as 1/8". Bottom line is, your spacing needs to be dead on. You didn't mention what type of jig you are using. Give us some more info and maybe we can help.

    Charter member of "I feel like an idiot club".


    • #3
      I vote for a I Feel Like an Idiot page to this web Site I am also a charter member of the club Man, Norm makes everything seem so simple.. [img]smile.gif[/img]
      Semper Fi <BR>Chuck<BR>USMC 66-70


      • #4
        Sorry about leaving out the details. I came across the plans for the jig in a Fine Woodworking issue while wandering the library stacks. It's very similar to one I've seen in Woodsmith (or maybe a ShopNotes) issue from several months back, except that it fastens the box joint jig to a crosscut sled. It uses an "indexing key" spaced to the right of the blade. My first cuts wouldn't align, but after scratching my head I noticed that the jig wasn't quite square to the saw blade. After fixing that, the fingers aligned beautifully, except they were way too tight! Then, I bumped the jig slightly toward the blade to make the fingers smaller thinking that would solve my problem - - I did get smaller fingers (a bit too small, actually), but the worst part is that the fingers went back out of alignment. Am I just being too careless and the problem is I keep going out of square? I understand the concept of the cumulative error, but on the other hand wouldn't the fingers tend to stay fairly close in alignment anyway since I'm always starting with the top of each piece.
        At this rate, I'll make the honor roll for the "idiot club"!


        • #5
          RJ, yes, you must be square. (Not you personally, but your jig to blade relationship). I don't know if your jig has any micro adjustment or not. The distance between the kerfs (fingers, if you prefer) must be identical to the width of the kerfs (slots). Get everything as square as possible. If you have a dial caliper, compare the kerf width with the distance between kerfs. Practice, practice, practice.