laying out a square / triangle
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  1. #1
    Join Date
    Jan 2010
    Location
    Sv. Filip i Jakov, Croatia
    Posts
    174

    laying out a square / triangle

    I'd like to know what's the procedure to make
    a large eg. 600mm long side) square/triangle ?
    I'm concerned about making it as square as possible.
    I'd like to use the square in woodworking, so am
    considering using stainless or aluminium.

  2. #2
    Join Date
    Mar 2018
    Location
    East Durham, NY
    Posts
    84

    Re: laying out a square / triangle

    Use the 3 4 5 method to make it square, also for rt angle triangle. Not knowing what you know, do you know the 3 4 5 formula?

  3. #3
    Join Date
    Apr 2010
    Posts
    2,173

    Re: laying out a square / triangle


    vjeko


    Here are some pictographs of the Pythagorean Theorem: aka 3-4-5 . . .
    For longer runs - any multiple of 3-4-5 works.

    http://www.google.com/search?q=pytha...HZ42Dq0Q_AUIBQ


    Opus

  4. #4
    Join Date
    Jan 2010
    Location
    Sv. Filip i Jakov, Croatia
    Posts
    174

    Re: laying out a square / triangle

    OK, thanks, pythagoras theorem is clear, maybe my question was not clear
    and my concerns are unfounded (I have concerns because my smaller bought
    squares are all out). I was mainly concerned about accurate measurement and
    checking before welding - do you just measure as accurately as possible / cut
    pieces and use a line perpendicular to an edge as check before welding ?
    For the line perpendicular to the edge, I was thinking of using a compass (make one)
    and bisecting two tangents.

  5. #5
    Join Date
    Jun 2016
    Location
    Not there
    Posts
    2,020

    Re: laying out a square / triangle

    Get it "square" with a square and tack it up. Clamp it tight.Then measure across, corner to corner.
    Most problems come from not having the iron the EXACT same length.
    8 feet and 8 feet+ 1/64 are miles apart when trying to make a window frame or something

  6. #6
    Join Date
    Jun 2016
    Location
    Not there
    Posts
    2,020

    Re: laying out a square / triangle

    Pull an inch.... or a foot. Never trust the hook on a tape.

  7. #7
    Join Date
    Nov 2014
    Posts
    267

    Re: laying out a square / triangle

    Quote Originally Posted by vjeko View Post
    OK, thanks, pythagoras theorem is clear, maybe my question was not clear
    and my concerns are unfounded (I have concerns because my smaller bought
    squares are all out). I was mainly concerned about accurate measurement and
    checking before welding - do you just measure as accurately as possible / cut
    pieces and use a line perpendicular to an edge as check before welding ?
    For the line perpendicular to the edge, I was thinking of using a compass (make one)
    and bisecting two tangents.
    Bisecting two radius arcs is a way to find a line perpendicular to another. I have used it often.
    Name:  find-90.jpg
Views: 436
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    I think I would make the triangle from a single piece of stock, what ever you think would work for you. I made some from acrylic and some small ones from thin aluminum.
    The check for perfect 90 is to flip the square and have no deviations on the same edge.
    Ernie F.

  8. #8
    Join Date
    Mar 2017
    Location
    Forest Grove OR
    Posts
    208

    Re: laying out a square / triangle

    Without a clamping table/fixture, it will be out of square when you are done welding it anyway. Sometimes you are better off preparing for this by adding a little compensation, or devising methods for re-squaring.

    I've used the 345 on vary large layouts, like laying tile in multiple rooms with no square walls where the layout needs to transition into multiple rooms seamlessly. Pick the layout line that has best match of the asymmetry, and then lay a perpendicular that is square to that layout. Any multiple of 3-4-5 works.

    I second the advice to pull an inch or foot (not trusting the tape end), it's easier to "see", though harder to hold.

  9. #9
    Join Date
    Apr 2018
    Location
    Norman, ok
    Posts
    2

    Re: laying out a square / triangle

    A method I have used is:
    start with a known straight edge
    Put the square against it and scribe a perpendicular line
    Flip the square along the straight edge (Mirror the inital step)
    scribe another perpendicular line from the same point of origin
    inspect the scribe marks if they are on top of each other you have a known good square
    if not a decision is made whether to bring into square or get another.

    This also a good method to determine a known straight edge. Scribe line flip over the scribed line and see if there is a belly.

    I have used this method to make fast squares for specific jobs, the largest of which is for building gates and follows the 345 method then checked with the above procedure. It measures 6' x 8' , suitable for 20' gates without using more labor intensive methods as I have in the past.
    Hope this helps, and if not clear I can do some photos demonstrating.

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