Discover the ten most common types of fixturing and what type of fixturing is best for your milling project in this CNC fixturing overview.

Workholding and fixturing can be challenging aspects of CNC milling. Designers have learned and shared several different ways to clamp parts into place throughout the decades. The ten most common fixtures range from CNC vises to self-fixturing and vacuum workholding.

John Saunders of NYC CNC created a video series that breaks down the top 10 CNC fixturing types, from soft jaws to custom fixtures. We’ve included all of his accompanying videos in this article to give you a closer look at each fixturing type

What is CNC Milling?

Before we get started, what is computer numerical control (CNC) milling? CNC milling is a machining process that utilizes computerized controls and rotating multipoint cutting tools to consecutively remove material from the workpiece to create a specific or custom part, product, or fixture. Hence, this process is faster and more precise than traditional machining processes. It’s also important to note CNC milling is not limited to metalwork.

Engineers can also manipulate plastic, glass, and wood for various applications. The milling process begins with a 2D or 3D product design in computer-aided design (CAD) software. Then, the engineer converts and prepares the file in computer-aided manufacturing (CAM) software in preparation for milling. They then load the product into the machine, and physical production begins.

Types of Fixturing

So, let’s take a look at the best ways to fixture material within the CNC machines, including vises, soft jaws, vacuum work holding, and more. Enjoy!

1. Vise Work

Many people are familiar with a traditional vice often used for woodworking or other home renovation projects. Traditional vices tend to have serrations or teeth that dig into the clamped object. CNC vises, on the other hand, use precision flat edges. The clamping power of a CNC vise is far greater than traditional vices. CNC vises use two inclined planes that act against each other. When the screw tightens, the top triangle pushes against the lower triangle on the movable jaw. As a result, this provides a strong clamping force forward and downward.

2. Soft Jaws

Soft jaws hold parts that would be difficult to fixture with standard, flat vise jaws during machining. You can 3D print or mill soft jaws to the exact specifications needed for various CNC projects and hold round objects. However, one downside to using soft jaws is accommodating the two screws that hold them to the vise. Machinists should also be careful to avoid any variation in diameter, tolerance, or size of the material held by the soft jaws. Uneven pressure can cause catastrophic failures.

3. Round Parts and Chucks

5C collets, expanding mandrels, and chucks hold round materials in a CNC vise, fixture plate, or fourth axis. 5C collets slide directly into the vise blocks and can be used on round objects from 1/16 of an inch to one inch. In addition, expanding mandrels are expandable cores that a product slides over. The mandrels push outward on the product from the inside with even pressure. Chucks are perfect for holding round objects vertically.

4. Large Parts

Large parts are usually items that will not fit in a traditional six-inch vise. Thus, they can be placed right on the CNC machine and milled easily using a fixture plate, mod vises, and other clamps.

5. Multi-Part Workholding

Multi-part machining workflows allow machinists to program CAD and CAM around multiple parts. This allows the CNC machine to make multiple parts at the same time. Further, dual-station vises allow for op one and op two programming coordinates.

6. Custom Fixtures

Custom fixtures are unique to the machinist’s needs. Utilizing Fusion 360 allows designers to create intricate workflows to machine custom fixtures for products that any other vises cannot hold. 

7. Vacuum Workholding and Thin Parts

Vacuum workholding gives about 14 pounds per square inch of holding power. This is an excellent alternative to holding thin parts that would not clamp well or get damaged in a different vise type.

8. Superglue Workholding

Unlike typical superglue applications, superglue workholding differs by applying a layer of tape between the fixture and the product. This keeps the superglue off of the CNC machine and product. This holding process can be paired with vacuum workholding when the part is large enough to require additional clamping force.

9. Tabbing and Window Machining

Window machining simplifies fixturing for the fixed stream for the second or third operation by letting the product/material serve as the fixture. This is accomplished by tabbing. A tab is a final piece used to hold a self-fixtured part.

10. 4th and 5th Axis Work

During 4-axis and 5-axis machining, the material dynamically moves in the CNC machine. Often in 4-axis machining, a collet or chuck is used. For smaller parts, a trunnion can help reach various rotational angles. You can also use the product as its own fixture. Custom fixtures can be made from material to attach directly to the product to hold within the machine.

Fixturing is a key component of any CNC milling project. Engineering is rooted in precision and innovation, and fixturing is another important step in the milling process. Thus, where there is material, there is a way to clamp it to produce even the most intricate designs.

Download Fusion 360 today to explore the wide variety of fixturing techniques for your next CNC project!