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"Types of Milling Machines"
Work Holding

Milling Types Home

Before we can begin to start making chips on the milling machine, the workpiece must somehow be securely fastened to the machine table. On most jobs that require milling, setting up the workpiece is the most difficult part of the job. Setups require critical thinking because not only does that part have to be fastened to the table, but the part must be positioned so that the proper surfaces can be machined using the correct features of the workpiece for positioning. If the setup is not properly planned and the accuracy is not insured in the setup, the part will probably end up as scrap. To insure a good setup, the operator must become aware of the types and proper uses of the work holding devices associated with milling machines.

Milling Machine Vises

The milling machine vise is the most common type of work holding devise used on the milling machine (Figure 1).

Figure 1: Plain Milling Machine Vise

The plain milling machine vise is used for holding work which has parallel sides. The vise is bolted directly to the table using the T-slots in the machine table. The plain vise can be accompanied by a swivel base (Figure 2).

Figure 2: Swivel Base

 Figure 3: Swivel Base and Vise

 The swivel base is graduated in degrees and allows the vise to swivel in the horizontal plane. The swivel base gives the vise a greater degree of versatility, but should be avoided when doing heavy rough cutting operations because it reduces the rigidity of the setup.

For machining operations involving compound angles, a universal vise is commonly used (Figure 4).

Figure 4: Universal Angle Milling Vise

The universal vise allows the operator to tilt the workpiece 90 degrees in the vertical plane as well as swivel it 360 degrees in the horizontal plane.

In high production situations an air or hydraulically actuated vise may be used. These types of vises are quick acting. They also maintain consistent clamping pressures from one part to the next. However, on most manual type milling machines the vise is opened or closed using a handle. When tightening a plain type milling machine vise it is not necessary to strike the handle of the vise (Figure 5).

Figure 5

Striking the vise handle with a hammer can either cause the vise to become over-tightened or cause the vise handle to break. If it becomes apparent that the vise is not holding properly, check with your instructor for other possible causes to the problem.

In Figure 6 please study the correct and incorrect vise clamping practices.

Locate the part in the center of the vise. This equalizes the pressure on the vise jaws.

Holding the workpiece off center puts unequal pressure on the vise jaws.  This can cause the piece to loosen up.

The workpiece should always be supported by the bottom of the vise or by parallels.

Work pieces that are not supported will move under the pressure of the cutting forces.

Keep the workpiece as low in the vise as possible.

Work that extends out of the vise has a greater chance of loosening up under cutting conditions.

Figure 6: Vise Clamping Principles For Milling

V-Blocks hold and support round work for milling or drilling (Figure 7). V-Blocks come in many different sizes. On milling machines, V-Blocks are typically clamped directly to the table (Figure 8).

Figure 7: V-Blocks

Figure 8: A V-Block and a strap clamp being used to clamp a round part to the table.

Angle Plates

An angle plate is an L shaped piece of Cast Iron or Steel that has tapped holes or slots to facilitate the clamping of the workpiece(Figure 9).Angle plates are used when parts need to have machining operations performed at a 90 degree angle to the axis of the table(Figure 10 ).

Figure 9: Angle Plates

Figure 10: Angle plate being used to machine the end of a long part.

Direct Mounting to the Table

Work that is too large or has an odd configuration is usually bolted directly to the table (Figure 11). This method of work holding takes the most ingenuity and expertise.

There are a number of accessories that can be used to help you set up the workpiece.

Figure 11: Direct Clamping using strap clamps-Notice the stop block. It is used to align the work as well as prevent the part from slipping.

A variety of commercially available clamp sets are available for directly mounting workpieces (Figure 12).

Figure 12: Clamping Sets

Parallels are pieces of steel bar stock accurately machines so that the opposing sides are parallel to each other (Figure 13). Parallels are provided in sets of two with identical dimensions.

Figure 13: Parallels come in sets of two.

Figure 14:
Parallels being used to raise the workpiece above the table surface.

Parallels are used in order to provide clearance under the work so the cutting tool does not damage the machine table or the vise base (see Figure 14).

In Figure 15 please study the correct and incorrect direct clamping practices.

Place clamp stud close to the workpiece.

Do not place clamp stud closer to the support

Use shims between finished surfaces and clamps

Clamps in contact with finished surfaces will mar the workpiece.

Clamps that are level or with a slight decline toward the workpiece will equalize the clamping pressure.

Angling clamps incorrectly puts pressure on the support, not the workpiece.
Place support parallels directly under clamps.
The spring caused by improper parallel placement will cause the part to bow.

Figure 15: Correct and Incorrect Clamping Practices

Milling Machine Fixtures

Fixtures are special work holding devices that are specifically designed to hold a particular workpiece (Figure 16). Fixtures are needed, in some cases, to hold odd-shaped parts which could not be held any other way. Castings are usually a good example of parts which need to be fixtured. Fixtures can also be used in high production situations. Supplying a fixture for machining the part can greatly increase productivity by reducing the time to position the part on the machine table.

Figure 16: Milling Fixture

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