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 Calculating Cross Sectional Area 
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Joined: Wed Feb 24, 2010 5:44 am
Posts: 444
Location: Mississippi Gulf Coast
When calculating a rectangular port with radius corners, how do you subtract the area of the radius?

Example: intake port opening 2.57"h x 1.91"w with 5/8" corner radius

Formula for calculating throat cross sectional area?

Ray

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Wed Dec 01, 2010 1:47 am
Profile YIM

Joined: Wed Mar 03, 2010 11:12 pm
Posts: 22
area of 5/8 dia = 3.142 x .3125 x .3125 = 0.3095 sq inch

area of 5/8 square = .625 x .625 = 0.5840

0.5840 minus 0.3095 = 0.2745 sq inch

subtract that from the large port area 2.57 x 1.91 = 4.9087

4.9087 - 0.2745 = 4.6342 square inches

hope you understood all this ..lol

Cheers

Lynds


Wed Dec 01, 2010 2:09 am
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Joined: Fri Feb 19, 2010 7:36 pm
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Location: Grantsville, Utah 45 min west of Salt Lake City
Lynds,
First of all nice hearing from you again! I appreciate your formula and it helped a bunch. I did it, but my math came out a little different.
area of a 5/8" circle that I did was Pi X R^ or 3.1416X(.3125X.3125)= .306796875
area of a 5/8" square is .625X.625 = .390625
so the difference I get is .083828125 and subtracted from 4.9087 gives me 4.824871875 square inches. Am I missing something or doing it wrong? Or did I get the correct answer?

John


Wed Dec 01, 2010 3:03 am
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Joined: Wed Feb 24, 2010 5:44 am
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Location: Mississippi Gulf Coast
Thanks Lynds and John.

I was confused with the formulas for Area of a circle and circumference of a circle.

Ray

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Wed Dec 01, 2010 4:57 am
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Joined: Thu Feb 25, 2010 3:39 pm
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this is some good math, and i have added it to my notes.

One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????

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Gordon


Wed Dec 01, 2010 2:16 pm
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Location: Mississippi Gulf Coast
Flash wrote:
One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????


You can use radius gages or make some using a hole template available from most office supply stores or drafting supplies.

Ray

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Wed Dec 01, 2010 2:56 pm
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Joined: Tue Jun 15, 2010 7:51 pm
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Location: So Cal
Flash wrote:
One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????


I also find using the unsharpened end of a drill bill useful sometimes.

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Wed Dec 01, 2010 6:27 pm
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Joined: Thu Feb 25, 2010 3:39 pm
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Sooo lets say i take a 1/4" drill bit and it fit perfection in the corner.......is that a 1/4 radius or 1/8 radius or...........................

And then do i times that # by 4 aka 4 corners? Before i subtract from to total?

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Gordon


Wed Dec 01, 2010 8:21 pm
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Location: Mississippi Gulf Coast
Devide 1/4" by 2 equals 1/8" or .250/2 = .125" radius

Or you could use this calculator Stan Weiss posted on Larry Meaux's forum to do the math:
http://users.erols.com/srweiss/index.html#jcalc

Ray

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Wed Dec 01, 2010 8:48 pm
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Joined: Thu Feb 25, 2010 3:39 pm
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Input Arc Radius o
Input Arc Diameter o


Yaah i seen that but was confused about my options

so if a 1/4" fit in each corner, i would enter .125 in each corner and then select Radius, not diameter...Right?

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Gordon


Wed Dec 01, 2010 9:06 pm
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