What are the parts of an engineer’s straight edge?

29th February 2020


What are the parts of an engineer’s straight edge?


	Shop for Engineer’s Straight Edges




		Working face
		The working face of an engineer’s straight edge (highlighted in red) is the flat surface that is placed in contact with the workpiece. ‘I section’ and ‘rectangular’ straight edges have two working faces.

		Supporting points
		The supporting points, or ‘feet’ of an engineer’s straight edge, are positioned on the opposite side to the working face, slightly in from the ends of the tool. By positioning the supporting points here, the straight edge will experience the minimum natural deflection of the working face (deflection due to the weight of the tool itself).

		Additional features
		Weight saving holes Weight saving holes are found mainly on large cast iron and steel straight edges. The holes are positioned along the length of the straight edge, keeping the weight to a minimum without affecting the rigidity and accuracy of the straight edge.

		On some very large granite straight edges, the weight-saving holes are also the supporting points that can be used for lifting the straight edge using a crane.

		Ribs Ribs (highlighted in red) are often used in conjunction with weight saving holes to minimise the weight of the straight edge whilst maintaining the accuracy required. Ribs distribute internal stresses (created by changing atmospheric conditions) evenly across the straight edge.

		Graduations These are marks of measurement sometimes placed on the side faces of a rectangular or knife edge straight edges. They allow the straight edge to be used as a ruler.



		Bowed and I section straight edges are not used for measuring, only checking the surface of objects are flat. So graduation marks are not found on I section or bow shaped straight edges. If you need a straight edge with graduation marks, you will have to use either a rectangular straight edge or a knife edge straight edge.

		Hanging holes Some smaller and thinner rectangular and knife edge engineer’s straight edges have a hanging hole on one end. This allows the straight edge to be hung up when not in use and minimises forces through the working face, so reducing any possible distortion of the working face.