Off Topic » in reply to Question: how do you find 3 points on a plywood circle 120 degrees apart, without a protractor?

Here you go, have a protractor:

podrock — 10/23/2006 4:35:57 PM (archived)

It's a layer from a 3D equal area net* I created in autocad:

It's much cleaner as a pdf file.

Graph paper and other useful pdfs can be obtained here

*a 2D graphic technique for analyzing the orientations of planes and lines in 3D space.

Log in or register to post.

The whole thread (37 posts)

• Question: how do you find 3 points on a plywood circle 120 degrees apart, without a protractor? (n/t) - RobVg - 10/23/2006 3:22:08 AM
  • Without a template, you put your anchor bolts in. Drill out the plate. - Bowser - 10/24/2006 6:34:51 AM
    • Slight addendum. - Bowser - 10/24/2006 3:41:35 PM
      • You are correct. - RobVG - 10/24/2006 4:26:51 PM
  • Yet another method - Fox - 10/24/2006 2:50:16 AM
    • Oops... Laurie beat me to it. - Fox - 10/24/2006 2:51:19 AM
      • Laurie beat me to it, too. - podrock - 10/24/2006 4:04:21 AM
  • Here you go, have a protractor: - podrock - 10/23/2006 4:35:57 PM
    • Or... - podrock - 10/23/2006 5:53:39 PM
    • Sorry, that's a compass. ;) (n/t) - RobVG - 10/23/2006 4:41:01 PM
      • Without the needle, it's a protractor. :) - podrock - 10/23/2006 5:01:16 PM
  • If I remember enough geometry... - alcaray - 10/23/2006 3:33:38 PM
    • Close. It's 2R sin (60 degrees). (n/t) - ER - 10/23/2006 5:16:08 PM
      • I used geometry, not trig... - alcaray - 10/23/2006 8:36:56 PM
        • What is "rad-5"? - ER - 10/23/2006 10:51:36 PM
          • final answer! - alcaray - 10/24/2006 5:09:43 PM
            • Correct! - ER - 10/24/2006 6:28:41 PM
  • Cut a circle out of paper, exactly the same size as your plywood circle - SDF - 10/23/2006 1:19:47 PM
    • Rule of thumb method. This is probably close enough for home carpentry. - ER - 10/23/2006 5:24:00 PM
      • Geometrically precise. Error comes from application - nick hoffman - 10/25/2006 12:36:46 PM
        • belay my last - it was just a senior moment - ER - 10/25/2006 2:56:07 PM
        • Another job for the CRC. - ER - 10/25/2006 1:33:16 PM
  • Yes, there is a way! - ER - 10/23/2006 11:04:03 AM
  • So... tell us what you're building! (n/t) - Laurie Street - 10/23/2006 5:18:08 AM
    • Backyard Observatory. - RobVG - 10/23/2006 4:02:47 PM
      • re: Backyard Observatory. - Laurie Street - 10/23/2006 4:10:28 PM
        • Sure. - RobVG - 10/23/2006 4:32:49 PM
  • Why can't you use a protractor? - ER - 10/23/2006 4:22:17 AM
    • Yes, there is a way! - ER - 10/23/2006 11:00:51 AM
    • re: Why can't you use a protractor? - Laurie Street - 10/23/2006 5:19:24 AM
      • Trisecting the angle--attention Mary Anne - ER - 10/23/2006 1:16:37 PM
        • While we're at it: Cameron's Hydraulic Tables? - Fox - 10/24/2006 2:35:29 AM
        • CRC Handbooks - Laurie Street - 10/23/2006 4:02:00 PM
        • Pocket Ref - SDG - 10/23/2006 3:34:20 PM
    • Because I don't have one smarty pants. - RobVG - 10/23/2006 4:40:17 AM
  • It's impossible - Laurie Street - 10/23/2006 3:35:48 AM
    • Thanks Laurie, your method is close enough. (now where did I put that string?) (n/t) - RobVG - 10/23/2006 3:44:38 AM