Jigs and Fixture

Jigs r provided with tool guiding elements such as drill bushes.These direct the tool to the correct position on the w/p. Jigs are rarely clamped on the m/c table bcz it is necessary to move the jig on the table to align the various bushes in the jig with the m/c spindle. Fixture hold the w/p securely in the correct position with respect to the m/c during operation. There is sometimes a provision in the fixture for setting the tool with respect to the w/p, but the tool is not guided as in a jig. Fixture are often clamped to the m/c table. Elements of J&F(Locating,Clamping,Tool Guiding & Setting Elements ) Adv of J&F(Productivity,Interchageability,Skill Reduction,Cost Reduction) Limits & Fits Diff b/w high and low limit , is called tolerance(unilateral,bilateral). Classification of Fits (Running,Push,Press Fit,Force Fit) Cost Estimation(Matl,M/cing,Heat Treatment, Assembling Cost) Principles of Location (1 Location must be related to the dimensional rqmts stated on the components drawing 2) It is prefable to use a more accurately m/chined surface than a less accurate surface Location, 3) The w/p should be prevented from moving along and rotating around X,Y and Zaxes 4) Location sys should facilitate easy and quick loading and unloading of the w/p and aim at motion economy 5) Redundant Locators must be avoided 6) Location sys should positevely prevent wrong loading of the w/p by foolproofing. Locating Methods of Plane Surfaces 1 A reasonably flat suface can be located by 3 pins of equal height having spherical surfaces at the location points 2 A rough, uneven or tapered plane should be loacted by 3 adjustable location pins having spherical ends 3 Additional adjustable supports are neccesary to prevent vibrations or distortion of the w/p during m/c operation. The force for adjusting the supports should be kept minimum so that the w/p doesnot get dislocated or lifted from the location pins 4) A machined surface can be located by pads having flat