Jig and Fixture: What is The Difference?

Jigs or fixtures? The two terms are easy to confuse. You’ll often find them paired together and despite sharing similar functions, the two are not interchangeable. Let’s learn the subtle differences between these manufacturing tools by examining how they are used to improve manufacturing quality, reduce production costs, and automate work.

What is a Jig?

A jig is a device used in securing a workpiece and machine part on a workstation. It is secured to the CNC machine tools such as a cutter, where it dictates the location and motion. That means, in a way, it guides such machining tools. Jigs are unique such that when they move, the tool becomes stationary.

You might know the term “jig” from your weekend fishing hobby, but it has a different meaning within the engineer’s lexicon. For our purposes, a jig holds the position of a tool in order to perform a manufacturing task. It’s often a custom part that ensures accuracy and repeatability when drilling and tapping holes.

Drill bushings are a common jig application. They help guide a drill through a workpiece in order to maintain accurate positioning and angle. Not only does it lead to higher quality work, but drill bushing can also increase manufacturing speed.

Types of Jigs

Jigs are common devices in CNC machining, and they come in different and various types. Below are the common types of jigs used in machining operations.

1. Template Jigs

These jigs are simple and ideal due to their accuracy. They also have tremendous speed. However, machinists use them more for accuracy than speed. Template jigs are used in many ways. For example, you can fit them over, on, or into the workpiece. However, they are not usually clamped.

2. Angle-Plate Jigs

Angle plate jigs are ideal for holding parts prepared for drilling at angles to their mounting locators.

3. Plate Jigs

Plate jigs are like template jigs with the same ways of use. However, unlike template jigs, they have built-in clamps to hold the workpiece.

4. Leaf Jigs

They have a hinged leaf which makes it easy to load and unload parts. The hinged leaf does not surround the part completely.

What Is a Fixture?

A fixture or CNC fixture is another popular CNC machining tool regarded as an agent of stability, support, and positioning. Like the jig, it works to secure, support, or mount a workpiece on a CNC machine.

How does a fixture differ from a jig? Rather than guiding a manufacturing tool, fixtures hold a workpiece in a secure position, orientation, or location. The vice on your workbench is also a fixture.

Fixtures are critical manufacturing tools that enable automation. You’d be hard-pressed to find an automated industrial process that doesn’t involve fixtures. An automobile assembly line, for instance, is not possible without the hardworking fixtures that secure and guide cars through the welding and assembly process.

They can also be used to hold a product in place for optical and laser scanning to assess manufacturing quality. Take a walk through a manufacturing facility and you’re bound to come across a fixture or two.

Types of Fixtures

Most machinists are not familiar with fixture classification. No wonder they have a problem with selecting the right one for their operation. The types of fixtures illustrated below are based on three things: machining operations, uses, and power sources. The list will be summarized.

Types of Fixtures Based on the CNC Machining Operation

• Turning Fixtures.
• Milling Fixtures.
• Drilling Fixtures.
• Boring Fixtures.
• Grinding Fixtures.

There are other types of fixtures based on the type of machining operation. We have concluded that every CNC machining operation that needs a fixture takes the operation’s name.

Therefore, for CNC machining operations like honing and lapping, you have CNC honing fixtures and CNC lapping fixtures, respectively.

Types of Fixtures Based on their Uses

• Universal Fixtures.
• Special Fixtures.
• Assembled Fixtures.
• Modular Fixtures.
• Combination Fixtures.

Types of Fixtures Based on their Power Source

• Manual fixture.
• Pneumatic fixture.
• Hydraulic fixture.
• Electric fixture.
• Magnetic fixture.
• Vacuum fixture.

Combining Jigs and Fixtures to Improve Precision

Using jigs and fixtures together helps achieve the manufacturing precision required for products to function properly. Take a look at your doors, cabinets, and shelving. The holes for the door’s knob, latch, and hinges require precise placement or guidance for drilling.

The same with cabinets with dovetail cuts or the shelving holes on the cabinet sides. Without jigs and fixtures, books would slide off the shelf, drawers would be flimsy, and doors wouldn’t close properly.

How to Manufacture Jigs and Fixtures

CNC machining is the most common manufacturing process for creating jigs and fixtures since volumes are typically low. In some cases, 3D printing is the most logical process when the geometry is too difficult or costly to machine.

It’s important to note that not all jigs and fixtures need to be made of metal. For many applications, plastic will reduce costs and meet your performance requirements.

Rapid manufacturing isn’t going to replace your current machine shops, but when utilized properly it can be a valuable tool for producing blanks for jigs and fixtures or less critical parts that don’t require high precision.

For a handful of parts, we recommend our CNC machining capabilities for your most common jigs or fixtures. If your part requires a more intricate geometry that’s difficult to machine, we would recommend 3D printing. For high volume needs, rapid injection molding can produce 25 to 10,000+ parts in a number of engineering-grade thermoplastics.

Design

Before designing a jig and fixture, there are some things you must know. Below is a highlight of the common things you must know

• Study the component.
• Study locating elements.
• Know the type and capacity of the machine.
• Know the loading and unloading arrangement.
• Get to know the clamping arrangement.
• Study the power devices and safety arrangement devices.
• Know the clearance between the jig or fixtures and their components.
• Study of ejecting devices, table fixing arrangement, and the indexing device.

Materials Use in Making the Jig and Fixture

Selecting a material to be used for making a jig or fixture depends on its application and machining operation requirements. Below are the materials used in making a jig and fixture.

• Steel (Stainless, Hard, Carbide, Mild, High Speed).
• Cast iron.
• Hardened Aluminum.
• Plastic: Derlin, Nylon, and PC.
• Bronze.

Use of the Jig and Fixture

The jig and fixture generally function in securing the workpiece and machine parts. However, there is a difference between both. With the fixture, the tool does not move when the workpiece moves. This is not so with the jigs where the tool moves. Depending on the types of jigs and fixtures, you might need to clamp also.

Advantages of Using Jigs and Fixtures

There are many advantages of using the jig and fixture in any machining operation. Below are a few important ones:

• Better Productivity and Efficiency: Because the two tools eliminate a workpiece’s alignment, a machine’s idle time reduces, which improves productivity and efficiency. 
• Decreases Manufacturing Cost: Their use decreases the product manufacturing cost while increasing productivity and quality.
• Improvement in Quality of Product: They remove the need for machinists to manually sets parts apart during operation. Therefore, this removes the human chance of creating error and improves quality.
• Easy to Manufacture Complex and Heavy Tools: They enable machinists to manufacture heavy and complex-shaped parts easily. This is because the two tools hold the workpiece rigidly during the machining operation.
• Improves Safety: Since the jig and fixture are directly involved in the workpiece and machine, they remove the involvement of humans, thereby increasing safety

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