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I REALLY NEED YOUR HELP (o/t)

2K views 33 replies 7 participants last post by  **DONOTDELETE** 
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#1 ·
OK guys, here's my dilemma. I know it sounds stupid, but i can't figure it out. The really sad part is that someone here WILL KNOW THIS!!

I need to build an OCTAGON. It has 8 sides, of course. The octagon must be 10 feet from one side to the other. What i need to know is this:
1) how long should each side be?
2) what angle should the joints be?

I have a few ideas...
does 4.1422 feet sound about right, and how about 135 degrees?


I wont tell you what this is going to be until my numbers have been verified.

I can fly a plane, save a life, or rebuild an engine...but this geometry stuff is above my head!

thanks a million, guys...

-mike

Give me Jeep or Give me Death!!!

(Will trade functioning organs for CJ-7 or flatfender)
 
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#4 ·
I assume that you are building a gazebo. . .

The process to find out the length is a long mathematical process that would take up a page of BBS and about four or five sketches too /wwwthreads_images/icons/crazy.gif!

Since I couldn't sleep and it is 0325, I would double check these figures by cutting eight strings to length, form them into an octagon, and then check the length of your sides. Or if you have a concrete slab large enough, just chalk it out with your chalk box and check it. Measure twice, cut once - remember?

Your length of the sides will be 5' 3 3/8" from outside tip to outside tip and your angle (the inside angle that you cut to butt the ends of the header joists together) will be 67.5º. In fact, your angle won't change no matter how large or small your octagon is - remember that!

I would suggest purchasing a "adjustable speed square." Stanley makes a nice one that is black with yellow lettering. It is a triangle with an arm that sweeps through it. It has a little knob on the end of the arm that you can tighten to set the arm at graduated angles. It will make marking your angles much easier, much faster, and more accurate when you lay this out. You will need it when you start cutting those rafters! I used to be able to mark these angles with a regular framing square - but that was back when I had something to prove to the crusty old farts on the job site /wwwthreads_images/icons/blush.gif. When I got out on my own and hired my own crew, I have all but forgot how to pick one up /wwwthreads_images/icons/laugh.gif.

In doing this calculation, I assumed two things: First, that you meant 10' from the outside edge of your header joists and not the inside edge. Second, that you meant 10' from the outside edge of your header joists on the flat side of the octagon - and not the corners.

Hope this helps. It should be close enough for you to tweak it from here.

Now I am going to get some sleep. Naaah. It's 0335 now - I might as well brew a pot of coffee and get busy!

When you come to the end of your road, get out and lock the hubs in . . .
 
G
#5 ·
4'-1 3/4 " sides, the corners are 45 deg, so each piece has a 22.5 deg. on each end, 10'-9 7/8" from corner to corner or 5'-4 15/16" from the center to any corner...love that autocad : )

looks like you had it right

 
#9 ·
Just because I had two minutes before work, I ran it in Cad and got the same as above.

pbm
74 cj5,304,t18,2.46 ts d20,30f,44r,soa,MORE buggy front,35's,Rci's,5pt,full cage,air,etc.
78 J10,360,727,d20,44f,44r,35's,4" lift,etc.
Support Search and Rescue.......Get Lost!
 
#10 ·
For the AutoCad guys:

Thanks for the correction on the length of the sides. /wwwthreads_images/icons/blush.gif After a few hours of work and a pot of coffee, I see where I made my error in calculation. /wwwthreads_images/icons/blush.gif BUT . . . Your program is measuring the angle of one header joist to the next - kind of like the angle of one side of the stop sign as opposed to the next. AutoCad is using this fomula: x = [(n-2)* 180 / n)] (where n = the number of sides.) Now to translate your angle into a real life cut to butt two pieces of wood together at a 135º angle, you need to divide that amount by 1/2: 67.5º. This is where your 45º comes in. The 45º is the inside angle at the center of the piece of pie.

Here is how you can see it in real life: draw a stop sign, then draw lines in from each corner to the center - kind of like cutting it up like a pie. Those corners that intersect in the middle of the pie are the 45º angles (NOT 45º CUTS THOUGH!!), and those outside corners where each slice comes together at the edge of the pie are the 67.5º angles.

Mike - just use my angles and their measurements and you should come out all right!

When you come to the end of your road, get out and lock the hubs in . . .
 
#11 ·
Looking back at the posts, if the side were 5'-3 3/8" at the outside edge, the overall circumference would be 13' 2 1/4", not 10'-0". So far the winner is 4'-1 1/16" sides (outside edge length) with 135 degree angles total, each piece mating the joint gets a 67.5 degree cut. There I had seven minutes at work to play.

pbm
74 cj5,304,t18,2.46 ts d20,30f,44r,soa,MORE buggy front,35's,Rci's,5pt,full cage,air,etc.
78 J10,360,727,d20,44f,44r,35's,4" lift,etc.
Support Search and Rescue.......Get Lost!
 
G
#13 ·
8 x 45 is 360 ...I don't know if he is building a deck or what, but my skil saw wont cut 67.5 deg. , it will cut 22.5 tho. , so thats how I descrided it...180 - 45 = 135...
90 45 = 135...45/2 = 22.5

If I'm wrong, there must be 1000 houses out there in the twilight zone, cause I've used those figures for 25 years, framing, triming or designing the bastids.
 
#15 ·
Your right, drawing it in segments at 45 degree angles give you the same thing as 135 degree inside angles/2 =67.5, Another difference in the comparison between the way you look at things. Anyway I think he'll be able to get it built.

pbm
74 cj5,304,t18,2.46 ts d20,30f,44r,soa,MORE buggy front,35's,Rci's,5pt,full cage,air,etc.
78 J10,360,727,d20,44f,44r,35's,4" lift,etc.
Support Search and Rescue.......Get Lost!
 
#16 ·
I'll throw in my .02

You didn't specify if 10' was from flat side to flat side or from point to point in the angles.

If it is side to side then the length of the long points on your boards should be 4'1-11/16"(4.14') the angle is 67.5. Using these measurements the entire octagon will fit inside a 10'9-13/16" diameter circle.

If it is point to point then the length of the long points on your boards should be 3'9-15/16"(3.83') the angle is 67.5. Using these measurements the entire octagon will fit inside a 10' diameter circle.

Solved with pencil and paper using a calculator (5 minutes).

Hope this helps. What are you building??

Later,

http://home.off-road.com/~tom85cj7/home.htm
 
#20 ·
Hell, with Pro/E you should have had time to model it, render it, get a bill of materials and run stress analysis on it :)

pbm
74 cj5,304,t18,2.46 ts d20,30f,44r,soa,MORE buggy front,35's,Rci's,5pt,full cage,air,etc.
78 J10,360,727,d20,44f,44r,35's,4" lift,etc.
Support Search and Rescue.......Get Lost!
 
G
#21 ·
Guys, i can;t begin to thank you enough for all your time, energy, and hard work. This proves one of two things...you are either the most generous bunch of guys on earth, or you've just got WAY too much time on your hands...either way, thanks a million...i felt my numbers were fairly close...but its been years since geometry class....

Now to hold up my end and tell you guys what i'm actually building...

FlMudCJ and I just rented a house, with a nice backyard patio and built in pool...with a decent amount of grass too. This octagonal structure is to be a Grand Splendor of a Tiki Bar. Yes, a Tiki Bar. You know, like luau style? Whenever you're done laughing....

But seriously, it is to be a full-fledged Tikibar...I went to Home depot today looking for Bamboo...and didnt see any...so i asked the man in the lumber department...after getting his smirk under control when i uttered the words bamboo, tikibar, and backyard all in the smae sentence he explained that he could not special order any, had none in stock, never did, and didnt know where i could get some...

I live in Daytona Beach, FL....i cant believe that bamboo could be this hard to find here...But, in any case, bamboo or not...if its done in time for the fourth of July, any of you local guys will be welcome to sit, have a cold one, and talk about Jeeps at the SWB Tikibar!!

thanks again,

mike

Give me Jeep or Give me Death!!!

(Will trade functioning organs for CJ-7 or flatfender)
 
#22 ·
So do we get a free Mai Tai for all the painful number crunching/ and mouse clicking?

pbm
74 cj5,304,t18,2.46 ts d20,30f,44r,soa,MORE buggy front,35's,Rci's,5pt,full cage,air,etc.
78 J10,360,727,d20,44f,44r,35's,4" lift,etc.
Support Search and Rescue.......Get Lost!
 
G
#23 ·
Well Pal... Home Depot ain't the place to buy anything that has to be "special ordered" ( they will RAPE U ) , But It sounds great !

Get busy finding the B-boo...it makes the job go smoother, if you know what you have for material. ; ) You'll have to step outside the box to build a "full Fledged tiki-bar" , but it should pay-off bigtime.

 
G
#26 ·
hmmm...I've checked my skil saws, jig saw, drill press, sawbuck, mitrebox, compound mitre box, table saw, band saw and chop saw, not one of those things will cut a 135 deg. cut ??? have I been cheated ? ...lol

 
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