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What is Square?
The idea of “square” is vital to woodworking. It refers to a square angle that is 90 degrees. So, when two pieces of wood come together to form a 90 degree angle not only is that angle square, but they are said to be square to each other.
When the face of a piece of wood comes to a 90 degree angle with its edge, that is also square. If all the faces and edges of a piece of wood or a project are 90 degrees, that piece or project is also called square.
Getting square angles in a project is important for the fit of the various pieces. You want to account for that in the project. Otherwise, if you need square 90 degree angles and you’re off, then the project doesn’t fit together properly.
Measuring For Square
Types of Squares
There are several common tools that measure for square. The first and probably oldest is the try square. This tool is simple and consists of 2 parts; a stock and a tongue. Put it up to an angle, either inside or outside, and if the parts register across the tongue and stock with no gaps, the angle is square – assuming this tool is actually square.
The try square is also great for marking a line that is perpendicular, or square, to the edge. The stock is made thicker than the tongue so that it registers against the edge. If the edge is straight and square to the face you’re marking on, then you can mark a square line across it. We do this to mark for crosscuts.
There are also tools like the speed square that are a bit different from a try square in that they can do some other carpentry measurements, but they aren’t able to measure an outside angle.
The combination square is the most versatile tool in the bunch but I’ve found that you have to spend quite a bit to get a good one unless you can find a good used one.
A combination square can do everything a try square does, but it also has a 45 degree edge for marking those angles, and it can be adjusted to a certain length and used to measure other parts that are supposed to be the same length. It can also be used to draw a line parallel to the edge.
This is a carpenter’s square, but it’s not the best for woodworking. I use mine from time to time for longer measurements, but not very often. It doesn’t have a shoe that registers against an edge, so it’s difficult to position it and be accurate.
The biggest square I have is a T square. This are used for drywall, but they’re also great for plywood.
All of these tools have their purpose, but they aren’t very helpful if they aren’t actually square, themselves.
Checking That a Tool is Square
There’s a quick way to “check for square”. Find an edge you know to be straight and flat like the factory edge of a piece of plywood. You can even place your straight-edge, such as the rule from your combination square, on the edge and make sure there are no gaps.
Hold the square up to it and draw a line. Now flip the square over and draw a second line touching the first. If the lines diverge from each other, at all, then your square is not….well, square. Again, this is assuming the edge you’re using is straight and flat.
Close is probably close enough, but if it’s significantly off, use a different square. There are ways to try an adjust certain ones, but I would just use a different one.
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