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Geometery question - table legs support

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  • Geometery question - table legs support

    Making a table for chop saw (wood type), using an old BBQ frame.
    Made tables that fold down on each side and would like to make support that pivots on bottom of table and on the verticle surface of the base and allow table to lock in place by going overcenter on the linkage. I have made these before for tablesaw but it was a trial and error method with lots of trials to get it lock up in the right place and be able to fold down without jamming. Understand the past center and locking part but don't know method of determing the length of the two arms using math.

    Anybody know a method?

    Gary

  • #2
    Law of cosines? I don't really know what you mean. I think i have a pic of it in my head but maybe a quick sketch could clarify.

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    • #3
      Trial and error!

      For stuff like this, I have become lazy and draw it up in CAD to figure out the angles, lengths, etc. I think I saw another thread saying Google has a free sketch program available now if you want to go this route and don't have a CAD program.

      I spent my days in the higher math classes studying the geometrical shapes of the female classmates
      Why buy it for $2 when you can make it for $20

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      • #4
        Right angle triangle

        Hi,
        look at it like a right angle triangle. The triangle has three sides.
        1. The long side called the hypotenuse
        2. the side across from the hypotenuse is called the adjacent side
        3. the side that joins the two sides above is called the opposite side
        The formula is the square of the adjacent side plus the square of the opposite side is equal to the square of the hypotenuse.

        So if the adjacent side was 10" squared would be 100"
        If the opposite side was 8" squared would be 64"
        Add them both together and you have 164" which is the square of the hypotenuse (long side)
        Now we calculate the square root of 164" which is 12.80"
        The square root means What multiplied by itself equals 164" and that was
        12.80"
        Now knowing the formula you can make the hypotenuse the folding strut to lock it down.
        Hope I explained this clear enough.
        Regards
        Chuck Marsh

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        • #5
          Why re-invent the wheel?

          Others have solved this problem. I'd just "borrow" the idea (just for"research" - of course) and adjust it to suit. The"toggle" principle is widely known and used. Hoods on baby prams/strollers, "fold-down tables" on sewing machine desks. Tables in furniture stores etc. And some of themare pretty strong and rugged. There's got to be lots of other examples.

          Why not find/"scrounge" what you need and either adapt it or your project to suit each other?

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          • #6
            Is it a right triangle though? What i have pictured in my mind must be different... thats why i suggested the law of cosines over the pythagorean thm.

            Oh and Wareagle - good call on studying geometry in the higher-level math courses!

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            • #7
              Thanks for the suggestions. Did a CAD drawing and it appears the offsets in the pivots don't make much difference.

              Looks like all that is needed is the length of support in extended position and the length difference of two fixed pivots in the folded position.

              Adding half of folded pivot difference to half of extended pivot length for one support arm and subtracting half of folded pivot difference to the extended pivot length for the other support arm..

              Maybe this only works when support arm is 45 degrees when extended and maybe this will only get me in the ballpark.

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              • #8
                Use of Pythagorean Formula

                Hello
                My thinking was that the junction of the table top and the leg provided a 90 degree junction so that information was the basis for using a Pythagorean formula to be able to calculate the hypotenuse.
                He can make the other two sides whatever he wants and then use the formula to find the length of the hypotenuse.
                He can also lengthen the hypotenuse just a little if he wishes to stress the triangle by going over center and having it lock and not fold up on him.
                This was given as a basis with which to calculate the lengths of the sides of the triangle for construction. This just the way I would have figured it. I'm sure there are many ways to do it.

                Regards
                Chuck Marsh

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