Design Consideration in Jigs

1. The major frame of jig should be strong sufficient so that the deflection of jig is as minimum as possible. This deflection of jig is caused because of the forces of cutting, clamping of the workpiece or clamping to the machine table. The mainframe of the jig must have the mass to prevent vibration and chatter.

2. Frames must be built from simple sections so that frames can be fastened with screws or welded, whenever essential. Those parts of the frame that remain intact with the jig can be welded. The parts needing frequent altering may be held with the screws. Where the body of jig or fixture has difficult shape, it can be cast from good grade of cast iron.

3. Clamping must be fast enough and require least amount of effort.

4. Clamps must be arranged so that they are readily available and may be easily removed.

5. Clamps must be supported with springs so that clamps are held against the bolt head wherever possible.

6. If the clamp is to swing off the work, it must be permitted to swing as far as it is essential for removal of the workpiece.

7. All of the locators, clamps must be easily visible to the operator and easily accessible for cleaning, positioning or tightening.

8. Provision must be made for easy disposal of chip so that storage of chips doesn't interfere with the operation and that their elimination during the operation doesn't interfere with the cutting process.

9. All clamps and support points that have to be adjusted with a wrench must be of same size. All clamps and adjustable support points must be capable of being operated from the fronts of the jig.

10. Workpiece must be stable when it is placed in jig. If the workpiece is rough, three fixed support points must be used. If workpiece is smooth, more than three fixed support points may be utilized. Support point must be placed as farthest as possible from each other.

11. The three support points must circumscribe the centre of gravity of the workpiece.

12. The surface area of contact of support must be as small as possible without causing damage to the workpiece. This damage is because of the clamping or work forces.

13. Support points and other parts are designed in such a way that they can be easily replaced on failure.