I haven’t read the math thread in the Tavern but………….how does one create a octagon within a given equal sided square?
I know it can’t be all that hard; it must be a division by degrees…………..I fuggled my way through it by trial and error but……………….
Help me please!
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Replies
Multiply length of side by .208 product is half side of octagon. Measure from each side of center.
The internal angle at each vertex of a regular octagon is 135° and the sum of all the internal angles is 1080°. The area of a regular octagon of side length a is given by A = 2a^2 cot frac{pi}{8} = 2(1+sqrt{2})a^2 simeq 4.82843 a^2. a circle with eight equal dots
i,m pretty impressed_______________________________________________________________
"Man," said Terl, "is an endangered species."
He's from Alabama...
Their octagons have 37 sidesI don't Know what I am doing
But
I am VERY good at it!!
LOL_______________________________________________________________
Now that is too much math. I am a keep it simple guy.
So a 30" square measured inside.............turned into an octagon each side (inside again) would measure almost 13" ?
Thanks a lot, and where do you get that from?
Eric[email protected]
That would be from a 1940's Audels Carpenters and Builders guide #1.
Been meaning to pick up the reprints. Awesome book.
It's about what is being lost.
Thank you.[email protected]
I dont know but my dad an old carpenter can do it on the framing square, I have some old steel square books that explain it, By the way its very hard to find those old books
Eric,
Try this method.
1/2 half the length of one side of the square is proportionate to 12" on 5/12 pitch on a framing square.
So 15"= 1.25 x 12", now multiply 5" x 1.25 =6.25".
6.25" is 1/2 the length of the side of the Octagon that is inscribed within a 30" square.
Edit: I made a typo and had "within a 15" square"
My apologies.
Length of side = 12 1/2 "
Edit: Helps to think of the Octagon in terms of a 5/12 pitch . Run = 1/2 the length of the side of the square, Rise= 1/2 the length of the side of the octagon.
"Poor is not the person who has too little, but the person who craves more."...Seneca
Edited 4/24/2007 8:44 pm by dovetail97128
Edited 4/24/2007 9:03 pm by dovetail97128
Thanks dove,
I'll print that and give it a try at the same time use dd'bugs math.
I framed the ro, but still need to fab a finish octa-jamb for believe it or not; a pass through from a kitchen to a dining room.
Thanks.[email protected]
As a PM it is now your responsability to dictate to your superintendant, or general foreman that they need to frame this for the job.
Simple, done!
I have to think about this but you can circle your square, and hash points from there. Been awhile but it works, might have to crack some books myself.
jeremy
The bad news is you've done exactly the right things to be exactly where you are today.
"IdahoDon 1/31/07"
With my method I come up with length of side of 49.92" for a 10' square.
.208 x 120" x 2
What do you have for a 10' square with your method?
1/2 of 10' = 5'5 x 5" = 25" =1/2 side of octagon 2x 25" = 50" I also have used . 41666666 (5/12) x 1/2 side of the square then mutiply that x 2. That method gives me .41666666 x 60" = 24.99999996" x 2 =49.99999992" "Poor is not the person who has too little, but the person who craves more."...Seneca
Edited 4/24/2007 9:45 pm by dovetail97128
Eric,
Do you have a Construction Master Calculator?
It is the dots on the framing square.
Chuck Slive, work, build, ...better with wood
Construction master is easier and faster.Joe Carola
I know you are a math guy but .208 x 30" x 2 is pretty fast and easy.
>>I know you are a math guy but .208 x 30" x 2 is pretty fast and easy.<<.414214 x 30 = 12.42641" (Length of all sides) is faster......;-)Joe Carola
Framer,
I agree the math is faster, but I love my framing square!!! Gonna be going the way of the horse drawn buggy if some of us don't keep using them, somebody has to keep the knowledge passed on. "Poor is not the person who has too little, but the person who craves more."...Seneca
Edited 4/24/2007 9:48 pm by dovetail97128
Thanks everyone!
What a great University we have here.
I now have at least four solutions to figure my octagon!
I'm goin to bed.
Thanks for all of your help, I really appreciate it.
Eric[email protected]
Eric,
Here is a lead on a great book.
Try to locate an older version of : "Kidder's Architects and Builders Handbook", Published by John Wiley and Sons.
Mine is the 17th. Edition, copy right 1921 It has a complete listing of factors for polygons starting with a triangle and going thru a dodecagon.
Factors are for area, radius of circumscribing circle, factor for length of sides factor for radius of inscribed circle.
Also has all the fornulas etc. This book is one of my building bibles. It has information on virtually every subject.
"Poor is not the person who has too little, but the person who craves more."...Seneca
Kidder's book.Abebooks.com
$35 + shipping.
Pete
Edited 4/25/2007 11:05 am ET by gotcha
ebay $9.99
be used, abused and transfused
I also have in my mind that seemingly wealthy, but most terribly impoverished class of all, who have accumulated dross, but know not how to use it, or get rid of it, and thus have forged their own golden or silver fetters.
Parolee # 53804
You win this time.
Nice to know so many places to shop.
Pete
Eric,If you want to draw something small and use the square, open this link from a few years ago.http://forums.taunton.com/tp-breaktime/messages?msg=36653.15Joe Carola
I love the framing square also, but it doesn't give you an exact size measurment for a room size octagon. The calculator is 100 times more efficient then the framing square for that.Joe Carola
you are thinking about this way to hard. lay it out with a framing square. If the octagon is in a 20 inch sq find your center point. From there make vertical and horizontal lines splitting the the 20 sq in to 4 sections. then make 45 degree runs through the center point. at that point you know that center point is 10 inches to the edge. run up each leg 10 inches all the way around. there is your octagon
Kodi,You posted to the wrong person.Joe Carola
No I do not.
I should perhaps. [email protected]
I like to multiply the sides by .414, which is the same as 1.414 divided by 3.414.
The reason I can remember this is I know that a right triangle with legs of 1 will have a hypotenuse of 1.414. If you look at an octagon as a collection of right triangles (see attachment) you will see that you can find any dimension you need by adding the right combination of legs and hypotenuses of a triangle of the size that you need for your octagon.
*edit- I had .29 as the factor, not .414.
Jon Blakemore RappahannockINC.com
Fredericksburg, VA
Edited 4/24/2007 9:41 pm ET by JonBlakemore
You can use a compass and protractor, too. Strike the circle and make marks every 45º. Connect the dots. 360º/8(sides)= 45º per corner
Eric,
Looks pretty simple to me but... Start by bisecting the square, both vertically and horizontally. Next draw another set of lines connecting the the corners of the square. Then start at the point where one of the bisecting lines meets the perimeter of the square and draw 22+1/2 degree lines into the opposing quadrants until they meet the lines which connect the corners. Repeat the last step from each of the perimeter bisecting points.
If I'm repeating what someone else has already suggested, it's because I fell asleep after about the first eight posts .
PS: After reading further, I yield to the method proposed by Kathleen in post #32. It's a distinct refinement of what I proposed above and it doesn't require any mathematics. For a carpenter, that's a noble solution.
Edited 4/25/2007 9:45 am ET by Hudson Valley Carpenter
Eric,
This might help as well.
Octagon layout calculator at
http://www.members.cox.net/ultimate_poker_table_top/Octagon%20Layout%20Calculator.html
You can also see directions on how to make a poker table there too.
In geometry you construct the shapes that you want using a straight edge and compass--no math needed!
Make your square.
Use a compass to find the midpoint of each side and mark the midpoints. (I suppose you could measure this, but I have problems reading a ruler so it's easier to construct it.)
Use a straight edge to draw the diagonals of the square. This will also provide the center of the square.
Set a compass to the distance from the center of the square to one of the midpoints. Use this setting to draw a circle inside the square, using the center of the square as the center of the circle as well.
The midpoints of the sides of the square and the points where the circle intersects the diagonals are the vertices of your octagon.
Kathleen
katiewa, Interestingly enough I was just looking at another way to draw the octagon. Draw your square, draw your diagonals.
Now set your compass from the corner to the center.
Draw an arc that intersects each of the adjacent sides from each of the corners.
You now have the octagon points layed out. At least that is the way I understood the directions and drawing.
"Poor is not the person who has too little, but the person who craves more."...Seneca
Interestingly enough I was just looking at another way to draw the octagon.
Excellent--even easier!!
Kathleen
you can use a framing square, the table is located on the face and tongue of the square
>I haven't read the math thread in the Tavern but.............how does one create a octagon within a given equal sided square?
Use the octagon tool in their CAD.