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best way to verify a 45 degree angle?

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Discussion starter · #21 ·
tjbnwi said:
I don't know, that's why I asked you.

Tom
Click to expand...
hehe, were you asking me how close the concrete was to 45 degree?

I don't know, I'll know monday morning.:laughing:

I'm kind of scared to find out. The 2 long walls are out by an inch over 30'
 
Discussion starter · #23 · (Edited)
m2akita said:
Did you actually pull that 44' 4 1/8" or is that what you got with SketchUp? If you actually pulled that measurement, you need to find some new concrete guys. They're setting the bar pretty high on quality!!!! :)
Click to expand...
I'm willing to bet it will be over an inch out. At least. Sometimes these guys are an inch out over 10':blink: I had to use a triple rim board on an entry way once.
 
#24 ·
Didn't read all the other posts so sorry if its already been said.
Knowing the lengths of the 3 sides you can use the law of cosines.
c^2=a^2+b^2-2abcos(C)
The C angle is across from the c side, using this for all sides you can determine all angles. Or you can find the one angle and then use the easier law of sines.
 
#26 ·
SuperiorHIP said:
Didn't read all the other posts so sorry if its already been said.
Knowing the lengths of the 3 sides you can use the law of cosines.
c^2=a^2+b^2-2abcos(C)
The C angle is across from the c side, using this for all sides you can determine all angles. Or you can find the one angle and then use the easier law of sines.
Click to expand...
The only knowns we're the lenght of the legs and one angle.

The base length was unknown. That is what he was looking to determine mathematically.

Tom
 
#28 ·
JT Wood said:
hehe, were you asking me how close the concrete was to 45 degree?

I don't know, I'll know monday morning.:laughing:

I'm kind of scared to find out. The 2 long walls are out by an inch over 30'
Click to expand...


It's ok... We're working off of a foundation that'd out 3 inches in 20 feet..........

It's an addition. HO said go with it. Alright, boss.....
 
#29 · (Edited)
Verify that the back wall and side wall are square to each other first.

Measure length of side wall to corner. Measure length from back wall to long point of angle wall. Subtract to find the difference. Use this number as the lengths of a right triangle and calculate the diagonal. If your angle wall is a 45, the number won't lie.

Example: Side wall is 30 feet. Length from back wall to point is 40 feet.

This leaves 10', or 120". Diagonal of 10' is 169.705".

If your diagonal doesn't match this length, the angle is off.

The same can be accomplished with unsquare reference walls by snapping square lines on top of the walls.

As for the 45 wall, you only need two numbers to establish a 45. Never trust the mason.
 
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#30 ·
kiteman said:
Are the lengths of the black lines the same? A line that bisects the point in the circle will create two equal right triangles. From there, Pythagoras takes over.
Click to expand...
Using this "equal right triangles" school of thought, w/a 135* deck angle, and a CMC.

Set Pitch = (180 -135) = 45* / 2 = 22.5*

Enter 22.5 [Pitch], 10' [Run], [Diag] = 10' 9-7/8"

The Black lines are 10'9-7/8" each,

The Red line is (2 x 10') = 20'

;)
 
#31 ·
JT Wood said:
Refresh my memory,

We are just starting a new frame, and I can't seem to remember how to mathematically verify the 45 degree angle on this foundation wall.

Normally the other (parallel) walls are long enough on a house, that I can run a 90 degree angle and get it that way.

So this is what I have.


The yellow lines are established as square.
The red circle is a 45 degree.
What I want to know, is

can I deduce the length of the red line given the length of the black lines, and the angle of the red circle?

For instance, If I pull the tape 24' on each black line, I get 44' 4"1/8 as the red line measurement.

BUT I cheated, I used sketchup.:laughing: Before Sketchup as invented, I would have run string lines and tried to get parallel measurements fron the string.

Anybody know the proper formula for this?

Thanks:thumbsup:


BTW what A nice view on this Acreage!
Click to expand...
What's the yellow line length?

That will b the diagonal of half the square of the two blue lines that should be equal.

Once you have the yellow line length from that rectangle you can get the exact length of the two blue lines.

What are the rectangle measurements?
 

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#32 · (Edited)
Birch said:
Using this "equal right triangles" school of thought, w/a 135* deck angle, and a CMC.

Set Pitch = (180 -135) = 45* / 2 = 22.5*

Enter 22.5 [Pitch], 10' [Run], [Diag] = 10' 9-7/8"

The Black lines are 10'9-7/8" each,

The Red line is (2 x 10') = 20'

;)
Click to expand...
How can this be if the OP states in the first post that the black lines are 24'? It has also been determined that the red line is 44'-4 1/8":eek:

Tom
 
#33 ·
JT,

I mentioned in an earlier post to use a calculator to find the sine. If you have an iPhone with iOS 7, you can use the calculator in Control Center (swipe up from bottom to access), turn the phone to landscape you have a scientific calculator with the trig keys. My guess is Android has something similar.

Tom
 
#34 · (Edited)
If the black line is 24', then the width of the rectangle should be 33' 11-5/16".

Just view the yellow rectangle in plan view with a 45° triangle off the end.

The width of the triangle is the diagonal of the 24' black line.

24 [Feet] [Run]

45 [Pitch] [Diag] Returns -33' 11-5/16"
 
Discussion starter · #36 ·
Joe Carola said:
What's the yellow line length?

That will b the diagonal of half the square of the two blue lines that should be equal.

Once you have the yellow line length from that rectangle you can get the exact length of the two blue lines.

What are the rectangle measurements?
Click to expand...

The reason I didn't us the "blue lines" to help is, I don't know if one or both or none of those walls are correct either. (not yet) So using that a benchmark to verify anything would likely not work out.
 
#37 · (Edited)
JT Wood said:
The reason I didn't us the "blue lines" to help is, I don't know if one or both or none of those walls are correct either. (not yet) So using that a benchmark to verify anything would likely not work out.
Click to expand...
What I'm saying is YOU make it work. You have the length and width of the rectangle yellow lines I drew. Those should be exact. If the foundations not square, you make your lines square. Now you can make the blue lines work out to an exact 45°.

What are the dimensions of the yellow rectangle?
 
Discussion starter · #38 ·
This is realistically the way I am going to verify this and other 45 degree corners from now on.

It's simple and easy for me personally to understand.
 

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Discussion starter · #39 · (Edited)
Joe Carola said:
What I'm saying is YOU make it work. You have the length and width of the rectangle yellow lines I drew. Those should be exact. If the foundations not square, you make your lines square. Now you can make the blue lines work out to an exact 45°.

What are the dimensions of the yellow rectangle?
Click to expand...

Not sure, the plans are on site. And I don't remember,

I re-read what you said.... you are right I agree:thumbsup:
 
#40 ·
JT Wood said:
This is realistically the way I am going to verify this and other 45 degree corners from now on.

It's simple and easy for me personally to understand.
Click to expand...
Whatever way is the easiest for you to undrestand is the best way.

I'm just suggesting to you that using the width of your rectangle is all you need to create the two black lines of your triangle, or the blue lines I made.

Since your black lines are 24', the width of the yellow lines in the rectangle should be 33' 11-5/16".
 
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