Date post: | 02-Apr-2018 |
Category: |
Documents |
Upload: | sayli-jadhav-sable |
View: | 254 times |
Download: | 1 times |
of 14
7/27/2019 7.Jigs and Fixtures
1/14
Jigs and Fixtures
What are jigs and
fixtures?
Used to hold and guidework pieces
Used to accuratelymanufacture duplicate
parts
7/27/2019 7.Jigs and Fixtures
2/14
A jig is a device that holds and locates a piece
of work and guides the tools that operateupon it.
A fixture is a device designed and built forholding a particular piece of work formachining operations.
Jigs and fixtures allow mass production ofconsistent quality. They also give added safetyby confining waste
7/27/2019 7.Jigs and Fixtures
3/14
Difference between Jig & Fixture
Jig Fixture
1. Used to guide and hold the workpiece 1.Only hold the workpiece
2.Used to drilling and related operations
only
2. Used for milling,
boxing,grinding,shaping
3. It is lighter in weight & construction 3. It is heavier in weight & construction
4.It reqires drill bushes 4. It require setting block
7/27/2019 7.Jigs and Fixtures
4/14
Degrees of freedom
Figure 3-1. The twelve degrees of freedom
7/27/2019 7.Jigs and Fixtures
5/14
Degrees of freedom
As shown in Figure 3-1, the twelve degrees of
freedom all relate to the central axes of theworkpiece. Notice the six axial degrees of
freedom and six radial degrees of freedom. Theaxial degrees of freedom permit straight-linemovement in both directions along the three
principal axes, shown as x, y, and z. The radial
degrees of freedom permit rotational movement,in both clockwise and counterclockwise radialdirections, around the same three axes.
7/27/2019 7.Jigs and Fixtures
6/14
A workpiece free in space canmove in an infinite number of
directions. For analysis, thismotion can be broken downinto twelve directional
movements, or "degrees offreedom." All twelve degreesof freedom must be restricted
to ensure proper referencingof a workpiece.
7/27/2019 7.Jigs and Fixtures
7/14
Basic Categories of Jigs
Clamps
Chucks
Vises Bushings
Modular Fixtures
7/27/2019 7.Jigs and Fixtures
8/14
Figure 3-2.The three forms of location: plane, concentric, and radial.
7/27/2019 7.Jigs and Fixtures
9/14
Clamps
7/27/2019 7.Jigs and Fixtures
10/14
Figure 3-3.Solid, adjustable, and equalizing supports locate a workpiece from a flat surface.
7/27/2019 7.Jigs and Fixtures
11/14
7/27/2019 7.Jigs and Fixtures
12/14
Bushings
7/27/2019 7.Jigs and Fixtures
13/14
Figure 3-15.Examples of redundant location.
Avoiding Redundant LocationAnother condition to avoid in workholder design is redundant, or
duplicate, location. Redundant locators restrict the same degree of
freedom more than once. The workpieces in Figure 3-15 show several
examples. The part at (a) shows how a flat surface can be redundantly
located. The part should be located on only one, not both, side surfaces.
Since the sizes of parts can vary, within their tolerances, the likelihood ofall parts resting simultaneously on both surfaces is remote. The example
at (b) points out the same problem with concentric diameters. Either
diameter can locate the part, but not both.
The example at (c) shows the difficulty with combining hole and
surface location. Either locational method, locating from the holes or
locating from the edges, works well if used alone. When the methods are
used together, however, they cause a duplicate condition. The condition
may result in parts that cannot be loaded or unloaded as intended.
7/27/2019 7.Jigs and Fixtures
14/14