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Four corners each greater than 90 degrees


Bob_Plumb's Avatar
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03-16-17, 04:46 PM   #1  
Four corners each greater than 90 degrees

So I was in a room and decided to put my speed square in each of the corners just for fun. To my surprise each corner was greater than 90 degrees. Last time I checked the sum of angles in squares, rectangles, and any parallelogram is 360. Yet each of the 4 corners is larger than 90.

So, I'm guessing its how the corners are made. Can anyone post a URL to a good page that illustrates how corners are typically made, and how that would explain what I have measured. Or maybe the walls themselves are not straight or something? Hmmmm, those lasers would show me wouldn't they?

 
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03-16-17, 05:19 PM   #2  
Start at a corner and use the Pythagorean Theorem. Go out on wall and make a mark at 3'. Then a mark on the adjacent wall at 4'. Measure between your marks and it should be 5'. No wall has been built square.

 
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03-16-17, 05:36 PM   #3  
Posted By: Bob_Plumb To my surprise each corner was greater than 90 degrees.
Think, "squared circle".

The walls are bowed or racked, which means you're not measuring true angles.
You're dealing with tangents.


( )

 
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03-16-17, 07:07 PM   #4  
There is a simple explanation. Your speed square is only 6" long. The way drywall corners are mudded, your square is sitting on the one or two degree angle created by the mud and tape. That alone tips the square away from the other wall. Add in the angle on the other side and makes the corner seem to be quite obtuse. That's why each corner seems to be the same. But that doesn't mean your walls are not square to each other. It only means that you've got some mud caked in the corners.

To measure a square or rectangle for square (square 90 degree corners), you measure the diagonals. They should match. If they don't match, you either have a rhombus or a parallelogram. But a speed square isn't going to tell you squat... it's too small.

 
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03-17-17, 04:57 AM   #5  
I agree with XSleeper. I have a 6' long ruler/straight edge. It's sometimes shocking when I put it up to an otherwise straight looking wall. The straight edge really points out where the sheetrock joinery was done. Those finely feathered joints can do a very good job of tricking the eye.

 
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03-17-17, 05:25 AM   #6  
There really isn't any such thing as a perfect house or even a perfect paint job BUT as long as you can give the illusion of a perfect job - you've done your job right


retired painter/contractor avid DIYer

 
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03-18-17, 05:25 AM   #7  
Start at a corner and use the Pythagorean Theorem.
Thanks a ton, I've been trying to remember these 'rules' from my school days because I know they have good practical use in carpentry. Feel free to post any others.

There is a simple explanation.
Yes, that is what I was thinking/hoping. I was looking for a URL to show my how corners are built but I suppose its a simple case of the sheets of jetrock meet, the corners are taped, and then a (hopefully) thin layer of mud is smeared in there.

There really isn't any such thing as a perfect house or even a perfect paint job BUT as long as you can give the illusion of a perfect job - you've done your job right.
Yes I agree. I think the goal has to be striving for perfection but knowing that you will easily magnify your time effort trying to get achieve that. Balance is key especially if you are do it for a living. Being off by a 'hair' doesn't usually break anything.

 
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