A try square is a simple but essential workshop tool used to check and mark 90° right angles. It has a long, thin metal blade fixed at a right angle to a thicker stock, often made of wood, metal, or plastic. Accurate right angles matter because small layout errors can make joints weak, surfaces uneven, and assembled parts misaligned.
In woodworking, metalworking, and general fabrication, the try square helps turn careful measurement into accurate work.
Understanding Tools & Workshop Machines: Try Square
A try square works only when its stock sits firmly against a clean reference edge. A reference edge is the edge chosen as the starting point for all measurements and marks. Put the stock flat against this edge, then let the blade lie across the face of the material.
Hold the tool still without forcing it. A pencil line drawn along the blade gives a cutting guide. For a check, hold the blade against the line or edge and look for light between the blade and the workpiece.
Light near one end shows that the angle or line is not square. This simple gap test is often more useful than trying to judge an angle by eye.
The order of work matters. First choose one straight, undamaged edge as the reference. Mark each needed line from that same edge.
If marks are taken from different edges, small errors can build up across the job. This is called accumulated error. A board may be only slightly out at each stage, yet the final frame can twist or fail to fit.
Students often see this when making a box, a picture frame, or a simple stool. Corners that are not square leave gaps.
A diagonal measurement can reveal the result. On a rectangular piece, equal diagonals are a useful sign that the overall shape is square.
A try square itself can lose accuracy after being dropped, bent, or exposed to moisture. It should be tested before important work. Draw a line against the blade on a straight board.
Turn the square over so the stock remains against the same reference edge, then draw a second line from the same starting point. If the two lines separate, the blade is not truly at a right angle to the stock. The distance between the lines shows the error.
Do not try to bend a damaged blade back by hand. Use another square or ask a teacher to check the tool. Dirt, wood chips, burrs on metal, and a nicked stock can create a false gap even when the square is accurate.
Good technique depends on steady contact rather than heavy pressure. Pressing too hard can tilt the stock, especially on soft wood or rough surfaces. Keep fingers behind the marking edge when using a knife or sharp pencil.
A marking knife can make a more precise line than a thick pencil, but it needs careful control and is usually used with teacher guidance. Read the line from the correct side before cutting, since a saw blade removes material.
In workshop tasks, check the angle after cutting rather than assuming the guide line was followed perfectly. This habit connects measurement, marking, cutting, and inspection into one reliable process.
Key Facts
- A try square checks and marks 90° angles between two surfaces or lines.
- The blade is the long, thin metal ruler used for marking and checking straight edges.
- The stock is the thicker handle that rests against the edge of the workpiece.
- For a right triangle check, a^2 + b^2 = c^2 confirms a 90° angle.
- Percent error = |measured value - true value| / true value × 100.
- A larger contact area between stock and workpiece helps improve squareness and stability.
Vocabulary
- Try square
- A measuring and marking tool used to check and draw accurate 90° angles.
- Blade
- The long, flat metal part of a try square used as a straightedge and marking guide.
- Stock
- The thicker part of a try square that rests against the edge of the workpiece.
- Right angle
- An angle that measures exactly 90 degrees.
- Squareness
- The condition of two edges, faces, or lines meeting at a true 90° angle.
Common Mistakes to Avoid
- Holding the stock away from the edge, because the try square cannot show a true 90° reference unless the stock is seated firmly against a straight edge.
- Using a damaged or bent blade, because even a small bend can make marked lines inaccurate across the length of the workpiece.
- Marking from a rough or unprepared edge, because the square transfers the error from that edge into every line you draw.
- Assuming every try square is accurate forever, because drops, wear, and poor storage can shift the blade out of square and require checking.
Practice Questions
- 1 A board is marked with a try square line across a width of 180 mm. If the line is 2 mm out of position at the far edge, what is the approximate error per 100 mm of width?
- 2 To check a corner using the 3-4-5 method, one side is marked 300 mm and the other is marked 400 mm. What diagonal distance should confirm a right angle?
- 3 A student presses the blade against the workpiece but leaves the stock slightly lifted from the edge. Explain how this affects the accuracy of the marked line and how to correct the technique.