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Table saw sled will not stay square!

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  • Table saw sled will not stay square!

    Being new to this art I decided I need a good table saw sled. With plenty of research I dove in using 1/2 " hardwood ply for the sled, oak runners, and glued two 3/4 ply to make an 1 1/2 fence. Using the principles of this video https://youtu.be/UbG-n--LFgQ ("5 cuts to a perfect Cross-cut sled") I have zeroed in to about .00005, which I have to say am a bit proud of based on my skill level! So at this point I have a nice square sled with a fence that has one screw at each end of the fence. As soon as I add a few more screws to really anchor the fence I lose my zero, to as much as 1/8th inch over 10". Reading the blogs there was mentioning of applying a bunch of clamps before adding additional screws but even that does not seem to help. Any ideas what I may be doing wrong? Any help is appreciated, seems like have done the 5 cuts to test the square so many times I may need to resharpen my new table saw blade!

  • #2
    Are you pre-drilling the screw holes? Plywood can/will move if screw holes are not predrilled with a hole the size of the screw shank (I guess that is what it is called.)
    Hank Lee

    Experience is what you get when you don't get what you wanted!

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    • #3
      I would consider drilling the hole in the base undersized and the hole in the fence oversized (of the screw shank).over the nearly correct locations.
      Then set the two end screws like you have done.to position for best square you can achieve.
      The put pan head screws(not flat head screws) in the hole engaging and cutting threads in the base while allowing some play in the fence position that will be locked when the screw is tightened. But allowing later movement if necessary.for adjustments.

      This basically prevents any side forces from being applied to the fence while turning the screw and only locking it when tightened against the base.
      Last edited by LCHIEN; 11-19-2018, 09:45 PM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - http://www.sawdustzone.org/forum/dis...sked-questions

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      • #4
        On a table saw sled the part that gets out of adjustment is the sled fence. If your table saw rip fence is reasonably square you can check your sled fence by butting a carpenters square tight against the saws rip fence and check the sled fence against the square. Like Lchien said, make the sled fence adjustable, forget about keeping it fixed, you will always be second guessing yourself and want to check and adjust it. I use a sled a lot. They are finger savers when cutting small pieces, but Donít get too comfortable using the sled though, the blade is just as dangerous with or without the sled, and you can still have pieces kicked back. Sleds donít accomidate the blade guard very well so you have to stay focused.
        capncarl

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        • #5
          I agree that you need to adjust the fence square, but have a different approach that I think helps with the OP's problem.

          What I do is to get the fence as square as is convenient at first, usually with a rafter's square, and glue it down. Screws, brads or clamps hold it as it dries, but the glue holds it after that. Once it's dry, I check it more carefully to be sure it is very straight, and very square vertically. Then I use the 5-cut method to check how close it is to square to the cut. Using that measurement, I apply tape to the fence to correct it precisely, then screw on a face to the fence, keeping screws away from the cut line. The face is mounted with a 1/8" gap below it as a sawdust space.

          This is solid, as it's glued down. It is easily adjustable by removing the face and shimming behind. I can renew the clean kerf for better measurement at any time. And it's fast and easy to do.
          Alan

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          • #6
            In case someone does not want to figure out how to use the 5-cut method to reset the fence, here's my approach. I fold a piece of tape in half twice, to make 4 layers, and measure its thickness with calipers. Let's call that T. The 5-cut method gives you two things, the length L, and the difference in thickness at each end of the cutoff D. To shim the fence, you need a distance = (L x T)/D. As you go along the fence, you add another layer of tape each time you traverse that distance.

            It's easy to figure out but a little trickier to describe which end of the fence should get more layers of tape because of variations in how you did the 5-cut method, and in what people call the front and back of the sled. Here's my careful wording that should be right no matter which side of the blade you cut on, or whether your fence is on the front or the back of the sled: If the end of the cutoff that was against the fence as you cut is wider, that means you want to shim so as to turn the fence in the same direction as you turned the piece while making the 5 cuts. That means more layers of tape on the end of the fence on the side of the blade where the big square was cut. If the fence end of the cutoff was narrower, shim the cutoff end of the fence more.

            Alan

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