Procedure in Designing for Jigs & Fixtures

The procedure for designing Jigs & Fixtures is governed through some principles.

1.     Rigidity:

-          The jigs and fixtures should be strong enough to held up the preset accuracy of machining.

2.     Fool Proofing:

-          It is defined as the,” incorporation of the design feature that will make it possible to lead the work into jig and fixture, in an improper position, but will not interfere with the loading and unloading of the work piece.”

-          There are many fool proofing devices, such as fooling pegs, blocks or pins which clears correctly positioned parts but prevent incorrectly loaded parts from entering the jig and fixture body.

3.     Clearance:

                 Clearance is provided in the jig or fixture body to allow for any:-

-          Variation in component sizes specially those of casting and forging.

-          Hand movements so that the work piece may easily be placed in the jig or fixture and removed after machining.

4.     Burr Grooves:

-          A burr raised on the work piece at the start of the cut is termed a minor burr and at the end of a cut is called a major burr.

-          Jigs should be designed so that the removal of the work piece is not obstructed by these burrs for the suitable clearance grooves or else slots should be provided.

5.     Ejectors:

-          The use of ejection devices is to force the work piece out from the jig or fixture.

-          It is important in the following cases:

Ø  When the work piece is heavy.

Ø  When the machining pressure forces the work piece to the slides.

Ø  When the pressure and oil or coolant fill causes the work to struck and makes it difficult to be removed on small jigs and fixtures.

Ø  When a pin located under the work removes the part radialy.

6.     Inserts:

-          To avoid any damage to fragile and soft work pieces and also to the finished surfaces of the work piece while clamping.

-          Inserts of some soft material such as copper, lead, fiber, leather, hard rubber and plastic should be fitted to the faces of the clamps.

7.     Design for Safety:

-          Jigs and fixtures must be safe and convenient in use.

-          Following are some of the factors for the safety of workers working on jigs and fixtures.

Ø  Sharp corner on the body of jig and fixture should be avoided.

Ø  Sighting surfaces should be cleared.

Ø  Bolts and nuts should be inside the body of the jig or fixture and not protrude on the surface.

8.     Sighting Surface:

-          Machining on the work piece must be clearly visible to the worker.

-          He should not be required to bend his neck for seeing the work piece or work surfaces.

9.     Simplicity in design:

-          Design of the jig and fixture should be a simple one.

-          A complete design requires maintenance.

-          They should be easy to set and manufacturing cost should be low.

10.               Economical:

-          Jigs and fixtures should be simple in construction, give high accuracy, should be sufficiently rigid and light weight.

-          To satisfy these conditions an economical balance has to be made.