How are engineer’s squares made?

29th February 2020


How are engineer’s squares made?


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		Heat treating
		Heat treating and tempering are manufacturing processes used to alter the physical properties of metal and other materials. Heat treating involves heating the metal up to a very high temperature and then quenching (rapidly cooling) it. This increases the hardness of the metal, but will also make it more brittle.

		Tempering
		Tempering is performed after heat treating, and also involves heating the metal, but to a lower temperature than required in heat treating, then letting it cool slowly. Tempering decreases the hardness and brittleness of the metal whilst increasing its toughness. By controlling the temperature the metal is heated to during tempering, it’s possible to alter the final balance between the hardness and toughness of the metal.

		Why is heat treatment and tempering carried out? Heat treating the blade of an engineer’s square makes it harder, so it will wear less from having a knife or scriber run along it. This helps it to keep its accuracy and last longer. Tempering is required to prevent the blade becoming too brittle which could cause it to break.

		Grinding
		Grinding is the process of using a bonded grinding wheel made of abrasive particles to remove material from a workpiece. The grinding wheel is a disc that is spun at high speed, and the workpiece is passed across the side face or circumference surface. Grinding can be done with discs made with grain sizes ranging from 8 (coarse) to 250 (very fine); the finer the grain size, the better the surface finish on the workpiece will be.

		Precision grinding Precision grinding is carried out by a very fine grain wheel on a machine such as a CNC (Computer Numerically Controlled) cylindrical grinder. The CNC machine allows precise control of the grinding wheel and workpiece, giving a more accurate finish than other grinding.

		Lapping
		Lapping is a finishing process used in manufacturing to achieve a smoother and flatter surface on a finished product. Lapping involves a lapping compound made up of abrasive grits and oils placed between the surface of a workpiece and a lapping tool. The lapping tool is then moved over the surface of the workpiece.

		The abrasive nature of the lapping compound wears away imperfections in the workpiece surface and produces an accurate and smooth surface finish. The most common types of abrasives used in lapping are aluminium oxide and silicon carbide, with a grit size between 300-600.

		Which gives the better surface? Lapping produces a better surface finish than even precision grinding and so is more frequently seen in the higher accuracy grades of engineer’s squares.

		How are the blade and stock attached?
		There are several methods of attaching the blade to the stock of an engineer’s square: welding, riveting or pinning and silver soldering can also be used. The most common of these is the use of three pins.

		Welding Welding provides the strongest connection between the blade and stock. It is also the least likely to move, which could affect the squareness and accuracy. Pins or rivets Pins or rivets, whilst being the most common way of attaching a blade to the stock, are more likely to move, affecting the squareness and accuracy.

		Engineer’s squares that do not have a stock have the two parts either welded together or the whole square will be machined from a solid billet (extruded bar) of metal. Engineer’s squares that are machined from a solid billet of metal are the strongest and will generally be of a superior quality.