Understanding Tools for Checking Flatness and Squareness

The question asks us to identify the instrument specifically used for checking the flatness and squareness of a surface. Various tools are used in workshops for checking dimensions, angles, and surface properties. Let's examine the options provided.

Analyzing the Options

• Go Gauge: A go gauge is a limit gauge used to check if a workpiece dimension is within the upper limit of the tolerance. It is a 'go' tool because if it fits, the dimension is acceptable. It does not check for flatness or squareness, only a specific linear dimension.
• Try square: A try square is a precision tool used primarily for checking if a surface or edge is at a 90-degree angle (square) to another surface or edge. The blade and stock of the try square form a perfect 90-degree angle. It can also be used to check for flatness by placing the edge of the blade on the surface and checking for any gap between the blade and the surface.
• Vernier height gauge: A vernier height gauge is a measuring instrument used to determine the height of objects or to scribe lines at a specific height from a reference surface plate. It uses a vernier scale for precise measurements. It is not used for checking angles like squareness or for assessing surface flatness directly.
• Centre punch: A centre punch is a hand tool used to make a small indentation in a workpiece. This indentation serves as a starting point for drilling, preventing the drill bit from wandering. It is a marking tool, not a measuring or checking instrument for flatness or squareness.

Identifying the Correct Instrument

Based on the analysis of the functions of each tool:

• The Go Gauge checks linear dimensions.
• The Vernier height gauge measures height and scribes lines.
• The Centre punch is used for marking.
• The Try square is designed specifically to check for 90-degree angles (squareness) and can also be used to check for flatness over a short span by observing light gaps under the blade.

Therefore, the instrument used for checking flatness and squareness of a surface among the given options is the try square.

Correct Answer Explanation: Try Square for Checking Flatness and Squareness

The try square is the appropriate tool for the stated purpose. It consists of a thick stock (handle) and a thin blade, rigidly fixed at a 90-degree angle. To check squareness, the stock is placed firmly against one surface (the reference edge), and the blade is brought into contact with the other surface. Any gap between the blade and the second surface indicates that the angle is not square (not 90 degrees). To check for flatness, the edge of the blade can be laid on the surface. If the surface is flat, the blade will rest evenly without any visible light passing underneath. While dedicated surface plates and straight edges are used for high-precision flatness checks, a try square is a common tool for checking flatness over smaller areas or when less precision is required.

Revision Table: Workshop Checking Tools

Additional Information: Types of Squares and Related Tools

Beyond the basic try square, several other types of squares and related tools are used for checking angles and surfaces:

• Engineer's Square: Similar to a try square but typically more precise, used in engineering workshops.
• Mitre Square: Used for checking 45-degree and 135-degree angles.
• Combination Square: A versatile tool with multiple heads (square head, center head, protractor head) that slide along a ruler, allowing for checking squareness, mitre angles, center finding, and angle measurement.
• Surface Plate: A highly flat, rigid surface used as a reference plane for inspection and layout. Used in conjunction with other tools to check flatness and straightness with high accuracy.
• Straight Edge: A tool with a precisely straight edge used for checking the straightness or flatness of surfaces by comparing the surface against the straight edge.

Each tool serves a specific purpose in the process of measurement, marking, and checking in manufacturing and woodworking.