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Thread: Figuring how to mark an angle....help

  1. #16
    Join Date
    Aug 2013
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    Providence, RI
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    517
    Quote Originally Posted by Derek Cohen View Post
    Basic stuff ....

    Mark a 45 degree line using a mitre square ( such as a combination square ... everyone has one?). Run this line and the baseline each for, say, 8", and then join them. The centre of this line, and back to the starting point, is 22.5 degrees. Take you less time to do than write this!

    Regards from Perth

    Derek
    Like Pat Berry's formula in #3 above, this is incorrect. The resulting angle would be about 26.6°. Again, trigonometric functions are not linear.

    At 8", a 22.5° angle requires a rise of about 3 5/16", not 4".

    If you were to draw an 8" arc from the end of the baseline to the end of the 45° diagonal, a 22.5° line would bisect the arc. But that is not the same as bisecting the straight line drawn between the two endpoints.
    -- Jim

    Use the right tool for the job.

  2. #17
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    Aug 2018
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    Michigan, USA
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    Quote Originally Posted by Jacob Reverb View Post
    Handy bookmark:

    What I like about it is that you don't have to jack around with sin, cos, tan, Oscar had a heap of apples stuff --
    When I was in high school, it was SOH-CAH-TOA - I like the "Oscar ..." bit, but I'd probably forget which order they're in!

  3. #18
    Derek is not saying the same thing as Pat. This method would work.

    He's not using the sides of a triangle, he's bisecting a sector of a circle. Blah blah blah. Dead horse, beaten

  4. #19
    Derek is correct. He created two identical right triangles that fit inside the isosceles triangle with the 8" sides. Half of the 45 degrees is 22.5 degrees.

    This whole discussion reminds me of the story of the math teacher who gives a protractor to his students and asks them to measure the height of a tall building. Many correct solutions, but none of them using the protractor and math tables.

  5. #20
    Join Date
    Apr 2008
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    East Virginia
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    830
    Quote Originally Posted by Derek Cohen View Post
    Basic stuff ....

    Mark a 45 degree line using a mitre square ( such as a combination square ... everyone has one?). Run this line and the baseline each for, say, 8", and then join them. The centre of this line, and back to the starting point, is 22.5 degrees. Take you less time to do than write this!

    Regards from Perth

    Derek
    Derek - I'm not following what you mean when you say "...and then join them." Could you elaborate for my feeble mind? I'm always up for learning simpler ways to do stuff.

  6. #21
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    Aug 2018
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    Michigan, USA
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    Quote Originally Posted by Jacob Reverb View Post
    Derek - I'm not following what you mean when you say "...and then join them." Could you elaborate for my feeble mind? I'm always up for learning simpler ways to do stuff.
    Maybe a picture - you can bisect any angle this way:

    Bisecting angles.jpg

  7. #22
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    Apr 2008
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    East Virginia
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    Thanks, Gary. For some reason the "and join them" was throwing me. I was trying to "join" the lines rather than their endpoints.

  8. #23
    Join Date
    Nov 2006
    Location
    NE Ohio
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    Thank you all! I was just trying to figure out how I could simply measure with a bit of math on larger panels and be fairly accurate before making the cut.
    I just use my 12" digital protractor, set to 22.5 degrees, to layout about a foot long line on the panel, then place my track saw track on the line and cut it.

    That's my simplified math method.

    The only time consuming part is taking the cover off and sticking the battery in the protractor, then taking the battery back out for storage.

    Makita and Festool both make a protractor attachment for the track saws that just slips on the track that are mechanical and require no battery, but, as far as I can tell - neither has a 22.5 degree or 45 degree stop, so a protractor is still required for setup.

    I don't wish to sidetrack the thread - but - so many people have the attitude that track saws are just for breaking down sheet goods, I like to point out how simple they can make other tasks.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  9. #24
    Join Date
    Sep 2013
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    Wayland, MA
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    Using a compass and straightedge to bisect the angle will produce a more accurate result, quickly, and with no error prone calculation math or measurements. It works for any angle.

    angle-bisector-construct.png

  10. #25
    Join Date
    Jun 2010
    Location
    twomiles from the "peak of Ohio
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    12,120
    Real problem: Desk sides.
    bad match.jpg
    Bad matching angles.....two pieces of scrap wood =
    angle guides.jpg
    Laid one over the other, make a cut ( or three) until things line up..
    test fit.jpg
    To cut this, I used a batten, and a circular saw...
    bevel and fence.jpg
    Once I get the top, and the lid ready....I'll report back as to what angles were cut...

    front view.jpglid opened.jpgside view.jpg
    Trying to build a sit-down version of this desk. Patterned after Underhill's Rachel's Standing Desk..

  11. #26
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    Feb 2004
    Location
    Perth, Australia
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    9,467
    Steven, simply use a sliding bevel gauge. You can gauge the centre by eye, and the rule off both sides. Plane to the lines.

    Regards from Perth

    Derek

  12. #27
    Join Date
    Jun 2010
    Location
    twomiles from the "peak of Ohio
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    12,120
    Getting set up..
    lay outs.jpg
    Might be a couple days....scrap block seems to be easier to hang on to....

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