DESIGN OF JIGS AND FIXTURES Chapter (1) INTRODUCTION
Guide for the drill Required hole Location of w.p. Clamping of w.p. Example of a drilling jig
The principles of jig and fixture design Loaction: (a) Ensure that the w.p. is given the desired constraint (b) Position the locators so that swarf will not cause mal-alignment (c) Make the location points adjustable if a rough casting or forging is being machined (d) Introduce foolproofing devices, such as fouling pins and projections, to prevent incorrect positioning of the w.p. (e) Make all location points visible to the operator from his working position (f) Make the location progressive (i.e. locate on one locator and then on to the other) (g) Ensure that redundant location is not present (i.e. two location points to control one constraint).
The principles of jig and fixture design (cont.) Clamping: (a) Position the clamps to give best resistance to the cutting forces (b) Position the clamps so that they do not cause deformation of the w.p. (c) Design the clamps so that they are not deformed by the clamping forces (d) If possible, make the clamps integral with the fixture body (e) Make all clamping and location motions easy and natural to perform. Clearance: (a) Allow ample clearance to allow for variation of w.p. size (b) Allow ample clearance for the operator’s hands (c) Ensure that there is ample swarf and cutting-fluid clearances (d) Allow clearance so that the w.p. can be removed after machining, when burrs may be present.
The principles of jig and fixture design (cont.) Stability and rigidity: (a) Provide four feet so that uneven seating will be obvious, and ensure that the forces caused by the mass of the w.p. and the cutting action act within an area enclosed by a line joining the seating points (b) Make the equipment as rigid as is necessary for the operation to be performed (c) Provide means of positioning and bolting the equipment to the machine table or spindle if required. Handling: (a) Make the equipment as light as possible, particularly if it is to be moved about by the operator for loading, etc. (b) Consider the shape of the equipment so that it can be handled easily; ensure that there are no sharp corners or awkward projections (c) If possible, provide lifting handles or lifting hooks.
The principles of jig and fixture design (cont.) General: (a) Keep the design simple in order to minimize cost and to avoid breakdown caused by over-complication (b) Utilize standard and ‘bought out’ parts as much as possible (c) Ensure that the w.p. can be loaded into and removed from the equipment.