Calibrating a square ensures its accuracy, which is crucial for precise woodworking, metalworking, construction, and other crafts. A calibrated square means it forms a perfect 90-degree angle, allowing for true square cuts and layouts.
Understanding Square Accuracy: The Flip Test Method
The most common and effective way to check if your square is truly accurate, or "in square," is through a simple method often called the "flip test" or "scribe test." This process allows you to identify any deviation from a perfect 90-degree angle.
Materials Needed:
- A flat, stable reference surface (e.g., a sheet of plywood, MDF, or a workbench with a straight edge).
- A sharp pencil or marking knife.
- The square you wish to calibrate.
Step-by-Step Guide to Checking Accuracy:
- Establish a Reference Edge: Position your chosen flat surface so one of its edges acts as a straight, reliable reference. This edge does not need to be perfectly square to the board, but it must be perfectly straight.
- Draw the First Line:
- Place the stock (the thicker base) of your square firmly against the straight reference edge of your surface.
- Position the blade or tongue of the square extending onto the main body of the surface.
- Using a sharp pencil or marking knife, draw a clear, crisp line along the inside edge of the square's blade. This is your first test line.
- Flip the Square:
- Crucially, do not move the reference surface or the board.
- Carefully lift your square and flip it over.
- Realign the stock of the square precisely against the same straight reference edge you used for the first line. The blade of the square should now be on the opposite side of your first line, extending over the surface.
- Draw the Second Line:
- With the square's stock firmly against the reference edge, draw a second line along the inside edge of the blade, right next to or directly on top of your first line.
- Interpret the Results:
- In Square: If your square is perfectly accurate, these two lines will be identical and perfectly aligned, appearing as one single, crisp line. Your square is "in square."
- Out of Square: If the two lines deviate, even slightly, appearing as two distinct lines that diverge from each other, your square is "out of square." The amount of deviation indicates how far off the 90-degree angle it is.
Calibrating and Adjusting Out-of-Square Tools
Once you've identified that your square is out of calibration, the next step depends on the type of square you own.
1. Adjustable Squares (e.g., Combination Squares)
Many combination squares are designed with an adjustable head that can be recalibrated.
- Adjustment Mechanism: Look for small set screws, usually hex or Phillips head, on the stock of the square where it meets the blade.
- Procedure:
- Perform the flip test as described above to determine the degree of error.
- Loosen the set screws slightly.
- Carefully adjust the blade's angle relative to the stock. Some squares might have a specific adjustment screw; others require slight manipulation of the head.
- Tighten the set screws and re-perform the flip test.
- Repeat this process of small adjustments and re-testing until the two lines from the flip test align perfectly.
- Tip: A small shim (like a piece of paper or feeler gauge) can sometimes be used between the blade and the stock to achieve very fine adjustments if the square doesn't have an explicit adjustment screw.
2. Non-Adjustable Squares (e.g., Framing Squares, Speed Squares, Try Squares)
For solid, non-adjustable squares, direct calibration isn't usually possible in the same way.
- Framing Squares & Speed Squares: These are typically solid pieces of metal. If they are out of square, it's often due to being dropped or bent.
- Minor Adjustments (Carefully!): For very slight deviations in metal squares, some professionals very carefully apply gentle pressure or tap the square with a mallet on an anvil to try and spring it back into square. This is a delicate process and can easily damage the tool further.
- Compensation: If adjustment isn't feasible, you can mark the amount of deviation (e.g., "1/32nd out over 12 inches") and mentally or physically compensate for it during layout.
- Replacement: For significant errors, especially in critical work, replacing the square is often the most reliable solution.
- Wooden Try Squares: These can sometimes be disassembled. If the blade is glued and screwed into the stock, you might be able to carefully re-glue or shim the joint to correct the angle, but this requires skill.
Why Accurate Squares Matter
Using a square that is even slightly out of calibration can lead to:
- Crooked Cuts: Miter joints won't close, cabinet carcasses will rack, and panels won't fit together correctly.
- Inaccurate Layouts: Walls won't be plumb, foundations won't be square, and frames will be twisted.
- Wasted Materials: Mistakes caused by an out-of-square tool often require re-cutting expensive materials.
- Frustration: Repeatedly fixing errors caused by inaccurate tools can be time-consuming and discouraging.
Types of Squares and Calibration Considerations
| Type of Square | Primary Use | Calibration/Accuracy Note |
|---|---|---|
| Combination Square | Marking, measuring, depth gauging | Often adjustable; can be calibrated with set screws. |
| Framing Square | Large layout, roof pitches, stair stringers | Solid construction; typically not adjustable (check for bends). |
| Speed Square | Quick angle finding, saw guides | Solid, cast aluminum; generally not adjustable. |
| Try Square | Checking small joints, marking joinery | Can be wooden or metal; some older wooden ones might be repairable. |
| Layout Square | Large-scale marking, construction | Similar to framing squares; accuracy is paramount. |
| Machinist Square | Precision metalworking | High precision; often non-adjustable; sometimes ground for accuracy. |
For more information on different types of squares and their applications, you can explore resources like Wikipedia's article on squares.
Maintaining Your Squares
Regular maintenance can extend the life and accuracy of your squares:
- Storage: Store squares carefully to prevent them from being dropped or bent. Hang them up or keep them in dedicated drawers.
- Cleaning: Keep them clean and free of rust or debris that could affect their flatness or edges.
- Regular Checks: Perform the flip test periodically, especially if the square has been dropped or is used frequently for critical work.
By understanding how to check and, where possible, calibrate your squares, you ensure that your projects start with accurate foundations, leading to better results and greater efficiency.
