Mumbai University > Mechanical Engineering > Sem 5 > Production process 3

Marks: 10 M

Year: Dec 2014

A jig is a special device that holds, supports, or is placed on a part to be machined. It is a 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 other cutting tools.

• A jig is any of a large class of tools in woodworking, metalworking, and some other crafts that help to control the location or motion (or both) of a tool. Some types of jigs are also called templates or guides. The primary purpose for a jig is for repeatability and exact duplication of a part for reproduction.
• An example of a jig is when a key is duplicated; the original is used as a jig so the new key can have the same path as the old one.
• Since the advent of automation and CNC machines, jigs are often not required because the tool path is digitally programmed and stored in memory.
• The most-common jigs are drill and boring jigs. These tools are fundamentally the same. The difference lies in the size, type, and placement of the drill bushings..
• Jig that expedites repetitive hole center location on multiple interchangeable parts by acting as a template to guide the twist drill or other boring device into the precise location of each intended hole center.
• In metalworking practice, typically a hardened bushing lines each hole on the jig to keep the twist drill from cutting the jig.
• There are many types of jigs, and each one is custom-tailored to do a specific job.
• Many jigs are created because there is a necessity to do so by the tradesmen.
• Some are to increase productivity, to do repetitious activities and to do a job more precisely.
• Because jig design is fundamentally based on logic, similar jigs used in different times and places may have been created independently.

Pot jig

• Pot type Jigs are used for the purpose of drilling holes in hollow cylindrical components
• Body of the Jig is similar to a pot and accommodates entire workpiece in it
• Clamp is provided inside which firmly adheres the workpiece, the clamp is projected from the drill plate which is located on top of the jig

Template jigs

• Template jigs are normally used for accuracy rather than speed.
• This type of jig fits over, on, or into the work and is not usually clamped.
• Templates are the least expensive and simplest type of jig to use.
• They may or may not have bushings. When bushings are not used, the whole jig plate is normally hardened.

Plate jigs

• Plate jigs are similar to templates. The only difference is that plate jigs have built in clamps to hold the work.
• These jigs can also be made with or without bushings, depending on the number of parts to be made.

Turnover Jigs or Leaf Jig

• Leaf jigs are small box jigs with a hinged leaf to allow for easier loading and unloading.
• Leaf jigs are normally smaller than box jigs and are sometimes made so that they do not completely surround the part.
• They are usually equipped with a handle for easier movement