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How to Square A Deck or a Carpentry Project Using 3 4 5 Method

How to Square A Deck or a Carpentry Project Using 3 4 5 Method
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One Thing I Make Use of on Almost Every Project

Knowing how to square things when building anything is very important and essential if you want your projects to turn out the best. Some people use a framing square but this is not very accurate since it is so small so we have to learn how to square a carpentry project using a method called 3 4 5. This method which is called the “Pythagorean theorem” and comes from good ole mathematics and geometry.

3-4-5-deck-framing2The “Pythagorean theorem” is a basic equation of  a2+b2=c2 where c represents the length of the hypotenuse, and a and b represent the lengths of the other two sides. So if we use 3 4 5 to replace a b and c we get this equation  32 + 4= 52 which turns into this – (3×3) + (4×4) = (5×5) which then turns into this 9 + 16 = 25 when we solve the equation.  Fairly simple is it not?

3-4-5-triangle-drawingWith this equation we can now use it to square our lines for our deck footings, use it to square the first joist to the house and other applications in carpentry projects as well.

Another tip with this method is you can use multiples of the starting numbers to measure over a greater length for more accuracy such as, instead of 3 4 5 you could use 6 8 10. So then your equation looks like this 62 x 82 = 102 which turns into – (6×6) + (8×8) = (10×10). And if we complete the equation we will have this – 36 + 64 = 100.

Out of all the geometry, trigonometry and calculus I took in school this “Pythagorean theorem” is the one thing I make use of on almost every project.

 

Tools required to square a carpentry project are:

  1. A good tape measure – one that does not bend over when you pull out 10 feet of length or so.
  2. A pencil or a sharper pen.
  3. A helper – your spouse, a friend, a partner – its pretty hard to be accurate doing this method without an assistant.

 

For another method of squaring you can read this post about how I square a box using the cross measure method which is making use of this 3 4 5 in a much different way.

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