Elongated Octagon Math ???

[Craig D Peltier]

My dad asked me to build him a stand for a grizzly. Its an elongated octagon.
Raised panel siding. Corners 22.5 degrees. Using 3/4 thick oak hardwood.

How do I figure the math on this? Its 6 feet long and 21.5 wide to the outside edges.
I need to know the width of the corners an the center piece of the side.

The non math way I guess I can make a scale rectangle. Make a 22.5 degree template with a 90 degree corner longer than needed to cross the lines an connect. I think math would be a bit more precise although.


Im sure its a (plane) geometry thing.Which I didnt take in school.

Thank you

[Chris Padilla]

Craig,

We need more information...I have no idea what this stand is supposed to look like.

Is the 6' x 21.5" piece the top of the stand? Is it just a rectangle with the corners lopped off?

I tossed this together in SU real quick but I dunno....

[Dick Strauss]

Craig,
Say you were to make a diagonal to replace a section of the cabinet corner. Say the sides of the corner that you want to replace with a diagonal are 6" each. The 45 degree diagonal would need to be roughly 6" times the square root of 2 (sqrt of 2 = 1.41) or 8.46-8.48" depending on rounding. This method only works for 45 degree diagonals.

For other angles you'd need to use Pythagorean theorem ((A*A)+(B*B)=(C*C) where A and B are sides of the corner and C is the diagonal). In the 6" example above we would have (6*6)+(6*6)= (8.46*8.46) using the Pyth theorem. If you had a 4" side and a 3" side, you'd end up with a 5" diagonal.

I hope this makes sense.

[Craig D Peltier]

Craig,

We need more information...I have no idea what this stand is supposed to look like.

Is the 6' x 21.5" piece the top of the stand? Is it just a rectangle with the corners lopped off?

I tossed this together in SU real quick but I dunno....

Yeppers , thats it

[Craig D Peltier]

I took a scale sized end drawing on the floor , measured in 6.25 from both sides. Just for a start.
Then 6.25 x 6.25 = sum then the same for other corner , then added those two numbers together an square root(ed) it. Came out to each panel being 8.83 I believe. I guess this is one way with trial and error on the math if you want all three panels to be the same width. Which is about 8 15/16th.
How about if I wanted to make the center panel much larger and the corners much less. How would I do that? Say 12 inch center panel and then the corners being solid oak stock ( no raised panel).

Heres pic of what im trying to make.

113446

[george wilson]

Just take a piece of plywood,and draw it out full size. Later,you can use the plywood for something else.

[Chris Padilla]

Ah, that is much better--pictures are always worth a thousand words!!

I did some more in Sketch-Up for you to give you an idea.

The dashed lines represent two things and I hope the difference is obvious.

First, they represent a 3/4" thick piece of wood.

Second, they represent a 6" mark from each side of the rectangle. I used 6" as an example.

The solid lines are wood. So a right triangle with 6" sides will yield a hyptoenuse of 8 31/64". sqrt[6^2 + 6^2] = sqrt(72) = 8.4853... ~ 8 31/64".

Notice that I joined two corners with 22.5 degree miters but it doesn't have to be done this way.

However, math is all nice and if you knew SU, it could help, but nothing beats drawing it out to full scale as George suggested. Start with cardboard if you need to or heavy poster board.

[Chris Padilla]

Here you go...done with my original 6" guideline above...18" high. :)

Thanks for the lunchbreak fun, Craig! :D

[Craig D Peltier]

Here you go...done with my original 6" guideline above...18" high. :)

Thanks for the lunchbreak fun, Craig! :D

How about for lunchtime tommorrow you change the width to 30 inches! Sounds like fun!:D My dad changed the width.

Thanks, I will look at this more thoroughly to understand
BTW on Sketchup how do you save the files to another format i.e. JPG or PDF. I have the free version.Not sure of that matters. Im new to it , so im just learning.

[george wilson]

I used to teach math,but I do not understand all the move to try to work everything like this out with math,when the sure and simple thing to do is just draw it out full size. Then,you are certain of where you stand.

[Tom Veatch]

...How do I figure the math on this? ...


The length of each of the 8 sides of a regular octogon is:

L = (.414 * X) where X is the width of the octogon across the flats.

For example, if X = 30", then the length of each side is .414 * 30 = 12.42"

If you want to elongate the octogon, simply increase the lengths of 2 opposite sides until the overall length is the size you want. For example: For an elongated octagon that is 30" wide and 72" long, then extend 2 of the sides the difference between 30 and 72 or 42". So those two extended sides would be 12.42+42 = 54.42". The other 6 sides would each be 12.42"

All dimensions are along the outer edges of the sides. Miter angles on the sides are all 22.5°

To save a file in the free version of Sketchup as something other than a .skp file, select the menu FILE/Export and select "2D Graphic" on the flyout menu. In the "Export 2D Graphic" dialog box, click the down arrow beside the "Export Type" dropdown box and select the image type desired. The available options are .png, .bmp, .tif, and .jpg. To get output as a .pdf, I print to a .pdf using a printer that was installed by Adobe Acrobat. Since the .pdf patent has expired, there are now other .pdf makers available from sources other than Adobe.

[Craig D Peltier]

The length of each of the 8 sides of a Thanks for the math an the sketchup help.
When I used an actrix type program. I would sne the file to print and use a pdf995 converter. It didnt print it but saved it to a pdf. I think thats what you mean.
Thanks




regular octogon is:

L = (.414 * X) where X is the width of the octogon across the flats.

For example, if X = 30", then the length of each side is .414 * 30 = 12.42"

If you want to elongate the octogon, simply increase the lengths of 2 opposite sides until the overall length is the size you want. For example: For an elongated octagon that is 30" wide and 72" long, then extend 2 of the sides the difference between 30 and 72 or 42". So those two extended sides would be 12.42+42 = 54.42". The other 6 sides would each be 12.42"

All dimensions are along the outer edges of the sides. Miter angles on the sides are all 22.5°

To save a file in the free version of Sketchup as something other than a .skp file, select the menu FILE/Export and select "2D Graphic" on the flyout menu. In the "Export 2D Graphic" dialog box, click the down arrow beside the "Export Type" dropdown box and select the image type desired. The available options are .png, .bmp, .tif, and .jpg. To get output as a .pdf, I print to a .pdf using a printer that was installed by Adobe Acrobat. Since the .pdf patent has expired, there are now other .pdf makers available from sources other than Adobe.

[Tom Veatch]

...It didnt print it but saved it to a pdf. I think thats what you mean.

Yep, that's exactly what I meant. The SketchUp help references "Export to PDF" as one of the options, but as best I can tell, that's a feature of the "Pro", not the "Free" version.