TYPES AND FUNCTIONS OF JIGS AND FIXTURES

1.      What is the difference between a jig and a fixture?

The difference is in the way the tool is guided to the workpiece.

-For jig, it is production tool made so that it not only locates and holds the workpiece but also guides the cutting tool as the operation is performed. Jigs are usually fitted with hardened steel bushings for guiding drills or the cutting tool.Small jigs are not fastened to the drill press table. However, holes above .25 inch in diameter are to be drilled, it is usually necessary to fasten the jig to the table securely.

-Difference with fixture, a fixture is a production tool that locates, holds, and support the work securely so the required machining operations can be performed.Set blocks and feeler or thickness gauges are used with fixtures to reference the cutter to the workpiece. A fixture should be securely fastened to the table of the machine upon which the work is done. Though largely used on milling machines, fixtures are also designed to hold work for various operations on most of the standard machine tool. Fixture also help to simplify metalworking operations performed on special equipment.

2.How are jigs  and fixtures normally identified?

Jigs and fixtures can be identified from the way of their operations.

Jigs are divided in two general classes : boring jigs and drill jigs.

Boring jigs are used to bore holes that either are too large to drill or must be    made an odd size. Drill jigs are used to drill, ream, tap, chamfer, counterboure, countersink, reverse spotface, or reverse countersink.

Fixture can be identified by a subclassification. For example, if a fixture is designed to be used on a milling machine, it is called a milling fixture.

3. What are set block used for?

        -Set blocks are used with fixtures to reference the cutter to the workpiece.

4.What class of jig would normally be used to tap holes?

         -Drill Jigs

5.A gang-milling fixture is actually what class of tool?

-Milling Fixture.

6.Analyze the following part drawings and operations to be performed and select the best jig or fixture for each.

a.       Figure 2-25. Operation: Mill a slot .250 inch by .250 inch

                                                  i.Vise-jaw fixture

b.      Figure 2-26. Operation: Drill four .500-inch-diameter holes.

                                                  i.      Plate jig

c.       Figure 2-27. Operation:  Drill four holes ( two .62-inch and two .25-inch )

                                                  i.      Channel jig

d.      Figure 2-28. Operation: Drill four holes, .50 inch in diameter.

                                                  i.      Template jig

e.       Figure 2-29. Operation: Mill a shoulder .75 inch by .75 inch by .38 inch.

                                                  i.      Angle-plate jig