How to calculate - Woodworking Talk - Woodworkers Forum
Old 06-19-2019, 02:57 PM Thread Starter
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How to calculate

How do I calculate this length. These boards meet at center top 45ed together and then extend down to wall where it meets them at a 45. Width needs be 84. How do I find out using math how long to make the pieces

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Old 06-19-2019, 03:28 PM
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You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.

In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.

George
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 The Following 2 Users Say Thank You to GeorgeC For This Useful Post: Onefreetexan (06-19-2019), wretched64 (06-19-2019)
Old 06-19-2019, 04:25 PM Thread Starter
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Quote:
Originally Posted by GeorgeC View Post
You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.

In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.

George
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

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Old 06-19-2019, 10:41 PM
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The top angle, is it a 45 degree angle or two miters making it a 90 degree angle?
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Old 06-20-2019, 06:29 AM
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I read it as 2 45's.

Hard to tell several areas, that is why I suggested more accurate drawing.

George
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Old 06-20-2019, 06:31 AM
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Originally Posted by wretched64 View Post
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

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If you want good answers, you must at least make them good enough so that responders can tell what it is that you intend to build.

George
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Old 06-20-2019, 06:42 AM Thread Starter
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If you want good answers, you must at least make them good enough so that responders can tell what it is that you intend to build.

George
Thought I explained the concept good enough. O well

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Old 06-20-2019, 06:43 AM Thread Starter
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Originally Posted by Steve Neul View Post
The top angle, is it a 45 degree angle or two miters making it a 90 degree angle?
2 45 angles making a 90

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Old 06-20-2019, 07:30 AM
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https://www.spikevm.com/calculators/...ter-length.php

Is this a shed roof? No matter as the calculations would be the same. Your drawing shows a 45 degree angle , which is a 12/12 pitch. Enter half of 7' (84") into the equation as the width and there you go.

Google how to calculate common rafter lengths and it will be clear. You might also read up on using a framing square as you can use it to step off lengths and then add any overhangs if you want and its just good to know how to use one.. They were the original calculators.

Or, you could just draw it out on a piece of plywood if you have one.
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Old 06-20-2019, 07:55 AM Thread Starter
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Originally Posted by Frost View Post
https://www.spikevm.com/calculators/...ter-length.php

Is this a shed roof? No matter as the calculations would be the same. Your drawing shows a 45 degree angle , which is a 12/12 pitch. Enter half of 7' (84") into the equation as the width and there you go.

Google how to calculate common rafter lengths and it will be clear. You might also read up on using a framing square as you can use it to step off lengths and then add any overhangs if you want and its just good to know how to use one.. They were the original calculators.

Or, you could just draw it out on a piece of plywood if you have one.
It's my starting point for a slat wall I start with those 2 pieces and work around then.

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Old 06-20-2019, 07:56 AM Thread Starter
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And 59.41 was exactly the length need for Long to short with 84 being the hard measurement. Tha is for help

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Old 06-20-2019, 08:24 AM
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The 59.41 sounds right. I drew it to scale and came up with 59".
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Old 06-20-2019, 08:58 AM
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I used the Pythagorean Theorem and got the same answer: 59.4 inches. Because of the way the angles are cut, the inside length and outside length are the same.

Side length = sqrt((84^2)/2) = 59.4
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Old 06-20-2019, 09:09 PM
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Originally Posted by wretched64 View Post
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

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Right On!

Tony B

Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Somerville, Tx
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Old 06-21-2019, 01:45 PM
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Quote:
Originally Posted by GeorgeC View Post
You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.

In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.

George
yeah, George nailed it!
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Old 06-22-2019, 10:27 PM Thread Starter
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Wall up and letters attached

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