Replies

1. 
   JerryPacMan | Mar 27, 2009 03:46pm | #1

   Maybe the link below will help.

   http://www.rockler.com/articles/display_article.cfm?story_id=98

    

    

   Life is what happens to you when you're making other plans.

   When your ship comes in... make sure you are not at the airport.

1. 
   mainerustic | Mar 27, 2009 07:53pm | #9

   Awesome, this calculator works wonders. It's almost too easy.thanks ... from Mainerustic

1. 
   charnwood123 | Mar 27, 2009 10:55pm | #10

   To calculate the angles of any shape with sides the same length and equal angles you can use the following equation

    

   2n -4 right angles

   where n is the number of sides

   so for an octagon

   2x8=16

   16-4=12

   12 right angles =12x90

   =1080

   1080 divided by 8(number of sides)

   =135 degrees for each angle

    

   Further example

   eg equilateral triangle (three equal sides in length and three equal angles

   2n-4 right angles

   2x3 =6

   6- 4 right angles

   = 2 right angles

   2x 90 =180 degrees

   180 degrees divided by three (number of sides in a triangle) =

   60 degrees for each angle

   This formula will work for any shape with sides of equal length and equal angles

   regards Charnwood

2. 
   KeithNewton | Mar 27, 2009 04:02pm | #2

   I am not sure I follow your dimensions, or what the 17" represents, but here is a simple way to mark and octagon while you make the parts.

   First cut two squares 17 x 17 if that is what the width should start as. Then find the center of each panel by carefully measuring in 8.5 from the middle of each side, or marking diagonally from corner to corner, then drill a small hole in both.

   Now lay one on top of the other, using a nail of the same diameter as the drill to pin them together. When you shift one 45º, each will be the template to mark the other.

1. 
   habilis | Mar 27, 2009 04:23pm | #3

   Nice trick!
   Pete

1. 
   KeithNewton | Mar 27, 2009 04:50pm | #4

   Yea, It is hard to beat the simplicity of that, since you would need to cut the squares first anyway. I used this recently when I made an octagonal chest with 11 tiers, and 88 drawers. My customer gave me the dimensions, and I remember being where Mainrustic is now. I was out in the shop wanting to get a feel for size, and to think about construction techniques. I cut a couple of scrap 1/4 mdf squares, and was trying to remember a geometric formula, when this just dawned on me. thanks k

1. 
   habilis | Mar 27, 2009 05:00pm | #5

   Seems so simple when you've got it. I think I might have a file on it in the mess in the back of my head. I frequently have the feeling there's an easy, simple, obvious solution I'm missing or forgetting. Great when I come up with it in time. Not as good when it's too late, but I'll remember it better.

2. 
   KiddervilleAcres | Mar 27, 2009 05:23pm | #6

   Hi Keith,

   First cut two squares 17 x 17 if that is what the width should start as.

   Most important step, the square has to be nuts on, eh? 

   Regards,Bob @ Kidderville Acres

   A Woodworkers mind should be the sharpest tool in the shop!

1. 
   habilis | Mar 27, 2009 05:55pm | #7

   I think pencil, ruler, protractor/compass would have to be just as accurate. And requiring more measurements, more difficult. I thought getting things dead on was the point. I can always use the practice.

2. 
   KeithNewton | Mar 27, 2009 06:04pm | #8

   That helps, but the Martins have already started arriving in AR, so Mr Mainrustic needs to just knock it out as quickly as he can, if he wants to have residences this year. I am not sure there will be enough tim for the paint to dry. For this kind of project, 1/8" caulk might be good enough. As for an unanswered part of his question. I think Sketch-up for Mac has the program for this.

1. 
   KiddervilleAcres | Mar 28, 2009 03:56am | #11

   Keith,

   I am not sure there will be enough tim for the paint to dry.

   Make 'em outa white oak and paint 'em this fall.  :-)

   Regards,

    Bob @ Kidderville Acres

   A Woodworkers mind should be the sharpest tool in the shop!

3. 
   Cincinnati | Mar 28, 2009 01:11pm | #12

   This depends on the accuracy you want. I'm assuming you want to cut a top and bottom plate that have 8 equal sides at 17" for each side length. Material thickness must be taken into account to get 17" as an outside dimension.

   To hit 17" exactly requires accuracy greater than 1/128".

   So to be practical — and assuming the birds won't know the difference:

   Draw a circle with a radius of 17-15/32" set on a beam compass.

   Set the compass to 17-1/64". Beginning anywhere on the circle, mark any spot on the circumference. Using the compass make marks along the circle 17-1/64" from the previous mark. Connect these tick marks along the circle and you have an octagon with sides approx. 17" long.

   Greg

   •••••••

   Exo 35:30-35

4. 
   Cincinnati | Mar 28, 2009 01:12pm | #13

   If you'd rather accomplish it using squares and a 45° triangle, let me know.

   Greg

   •••••••

   Exo 35:30-35

1. 
   mainerustic | Mar 28, 2009 05:19pm | #14

   Good suggestion, I'll try that, but now you've got me curious, how could it be done
   with a try square?Thanks again

2. 
   mainerustic | Mar 28, 2009 05:20pm | #15

   Good suggestion, I'll try that, but now you've got me curious, how could it be done
   with a try square?Thanks again

1. 
   Cincinnati | Mar 28, 2009 10:00pm | #17

   Draw a straight line 17" long. The included angle at the points in an octagon is 135°. Notice that 180° - 45° = 135°.So use your 45° triangle to strike a 17" long line at the end of the first baseline offset by 45°. Using this line as the new baseline, strike another 17" long line at a 45° offset at the endpoint of the last 17" line.Continue doing so until you get the octagon completed. If I'd have thought through the process of doing this, I would have recommended this method over the one with the compass. But the one with the compass involves much less measuring. OR: Combine the two. Every time I mention to measure 17", use a compass set to 17" and strike an arc to intersect each 45° line. That intersection point is the reference for the next 45° line.Greg••••••• Exo 35:30-35

   Edited 3/28/2009 3:04 pm by Cincinnati

1. 
   mainerustic | Mar 29, 2009 12:08am | #18

   Awesome! This really does work and it's very easy to do.Thank you all for your suggestions...

2. 
   knuts | Mar 29, 2009 04:19pm | #19

   View Image

    

   Here's another graphic.

1. 
   habilis | Mar 29, 2009 06:52pm | #20

   Neat graphic! How ya do dat?

1. 
   knuts | Mar 29, 2009 08:54pm | #21

   Animated GIF..

5. 
   jbob | Mar 28, 2009 06:59pm | #16

   I would draw the octagon in SketchUp and then get the side lengths with the tape tool and angles les with the compass tool.
   Robert

6. 
   Mr.Supey Dupe | Apr 06, 2016 07:19pm | #22

   octagons

   A real good link is on Goole.ca or .com Just type in "octagon layout calculator"  type in the fetet and the rst will come up automatically. I have used it many times to make coffee (drink) tables for the back yard. the corners cut off get glued and screwed to the under side if the table 3/4 spacing to hold the legs