Geometry sucks!

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Hamberg

Hamberg

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Good at math but geometry eludes me - algebra, no issues; figuring out a mitre angle, and I'm on the floor in a fetial position crying :mad:!

My go-to method has always been trial and error - little cuts until the joint works. But there has to be a better way?? Some, super secret, carpenter only method that is only accessible via some sort of industry handshake??

Example below (from a deck railing I was installing yesterday) - could someone (anyone) please explain an EASY way to figure the angle(s) needed to make this joint?

Angle.jpg
 
Is that 90 degree location an outside wall? What are you trying to achieve? Sometimes crooked walls are just part of doing business, but the straight line should be aesthetically pleasing to the eye. The way your drawing shows, the ?? area is also 90 degrees.
 
havasu said:
Is that 90 degree location an outside wall? What are you trying to achieve? Sometimes crooked walls are just part of doing business, but the straight line should be aesthetically pleasing to the eye. The way your drawing shows, the ?? area is also 90 degrees.
Click to expand...

Hey @havasu for example purposes, the 90 is an out side wall. The railing was on a (concrete) porch and was far from square. Although, without the railing, cosmetically it looked fine.

Here is a more exaggerated example of what I'm talking about - assume the ?? lines followed the porch footprint, how would the two mitre angles be calculated?

Angle1.jpg
 
If they point where the ?? are, isn't, 90 degrees, then set a speed square on one side and the degree of difference will be revealed. Divide the difference in two and that's the degree of adjustment for the cut.
 
All 4 corners of a square will equal 360 degrees. Using a adjustable T square, you find that angle, then the remaining angle will need to add up to 360 degrees. But as said earlier, you just need to have the project aesthetically pleasing to the eye, so "wing it!"
 
Then you would have an oblique angle.
"The definition of an oblique angle is one that is not 90 degrees. ... An angle, such as an acute or obtuse angle, that is not a right angle or a multiple of a right angle."
I would have to pull out my geometry books for that.

However, in the pic above, your unknown would by 92 degrees. Hell, you got my brain smoking now.
 
I hate Math so much that after reading this, I have no idea what you want to do. When I need an angled cut, I guess and use a scrap piece until I get the cut exactly right.
 
Nothing wrong with making a cardboard pattern. Many granite counter installers hot glue furring strips to the exact angles needed, and they come out perfect and best of all, no math is needed.
 
I have traced an angle onto paper then folded to bisect the angle.
 
All I'm remembering is Pythagorean's theorum and my Sikh geometry teacher saying "Right angles are congruent" in an Indian accent...
 
In your example, only the top railing needs to have the miter angle cut. Take two pieces of the material you will use for the top rail, cut slightly longer than needed. Then lay one on top of the other in the position they are going to be and mark both sides of the top board onto the bottom one. Then reverse the boards putting the other one on top and mark both sides on the other one. Now draw a line from the inside corner of the marked line to the outside corner om both boards. This is the angle to cut.
 
Just a thought, use the video technique to mark and cut the first rail then with the rails in place trace a line on the second rail. BTW it's looking good!

Here's another trick for an inside miter;

 
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