Help a dunce? Need formulas for angles and heights to design a frame.

Discussion in 'General Math' started by Mike Barnard, Aug 13, 2006.

  1. Mike Barnard

    Mike Barnard Guest

    Hi all.

    Thanks for reading this. I have done little math (apart from counting
    my change) since I was at school in the 60's. I now need to calculate
    some angles and heights but don't know the formulaes. Can you point
    me to sites that give help, please?

    Why? I need to build a wooden shed. (Boring!) I know the heights I
    want of the back and front walls, but to accurately cut all the pieces
    that make a shed I need to work out the angles and heights at various

    For example:

    The back wall is x mm high.
    The front wall is y mm high.
    The shed will be z mm deep, front to back.

    What angle do I cut the tops of vertical timbers to to match the roof?

    What height do I cut a vertical timber to at n mm from the back wall
    to intersect the roof?

    And other sundry questions that will arise!

    So can you math experts point me to a place I can get my formulas,
    please? I *have* googled and found anything but what I need.

    Thanks in advance.
    Mike Barnard, Aug 13, 2006
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  2. Mike Barnard

    Peter Webb Guest

    The secret is to reduce everything to triangles, and use the "Law of Sines"
    and "Law of Cosines" (as well as Pythagorases thereom, which is a special
    case of the rules). You can Google them; if you don't understand how they
    work, post your questions.
    Peter Webb, Aug 14, 2006
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  3. Can you add, subtract, multiply and divide?
    Since you pride yourself with self imposed mathematical ignorance, I'll
    suggest methods that don't require any more math than counting change.
    Draw a plan of the side wall to scale and measure the angle.
    Oh no, you are measuring in millimeters?
    Already you are doomed to a doll house
    200 mm high, 100 mm low, 1000 mm along.
    arctan((y - x)/z)
    Are you cutting them off level or at the bevel?
    If the later, what do you mean by height?
    As the answers to these questions involves math,
    how could they be of use to you?
    William Elliot, Aug 14, 2006
  4. Mike Barnard

    Mike Barnard Guest

    On Sun, 13 Aug 2006 20:16:18 -0700, William Elliot

    [Snip a page of unnecessary insults, vile invective and exposure of
    small balls.]
    I don't know what makes you such a worthless poster, but it really
    works! You wouldn't know Up from Down if you had three guesses.
    Reading your post makes blindness a wonderful thing to look forward
    to. You bring to mind a quote from Josh Billing: "Doesn't know much,
    but leads the league in nostril hair."

    <Jonsey mode>

    Killfiling now sir...

    Mike Barnard, Aug 14, 2006
  5. Mike Barnard

    Mike Barnard Guest

    Thanks for a sensible, reasonable answer. I haven't needed this sort
    of math for many years now and need a refresher.

    Googling for all the above now.
    Mike Barnard, Aug 14, 2006
  6. Mike Barnard

    Mike Guest

    Hi Mike,

    I wouldn't fret too much on advanced trig. Assuming you are building a lean-to shed (where the front and back walls are
    rectangular, with the front higher than the back, and the side walls slope from front to back) - you only need to use
    trignometry if you want a specific roof angle, and that is to determine the difference in front and back height to get
    the required slope of the roof.

    Front and back walls are rectangular, so all the joists (the verticals) are the same length (x and y respectively - or
    x - 2d and y - 2d where d is the thickness of the top and bottom plate). No trig here.

    Side walls. The front and back joists will be of length x and y respectively with the top end cut to the same angle as
    the roof line. Assuming the side walls have length z then an intermediate joist along the side wall set distance w back
    from the front wall will have length ( zx + wy - wx ) / z .

    Of course, in practice, the best way to build the side walls is to cut the base plate of length z, and th efront and
    back walls of lengths x and y (with sloping top) - then lay them on a flat surface and nail thet together. Square the
    front and back joists, and nail on a slightly over-length top plate. Now you can mark where you want the intermediate
    joists (here in New Zealand they would be at 600 mm centres along the sides), and measure between the top and bottom
    plates to determine the required length. In other words, it is better to ct to the measured length rather than pre-cut
    everything, unles yopu are trying to build a prefabricated or kit-construction. So if you use trig, you only need to
    use it once, and if you just want a roof with a 1:6 slope, you don't need trig at all.

    Good luck,

    another Mike
    Mike, Aug 15, 2006
  7. Mike Barnard

    Mike Barnard Guest


    Apart from it being higher at the back than the front you're spot on!
    Grin. Thanks for the helpful info.
    Mike Barnard, Aug 15, 2006
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