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"Milling Machines"
Tool Holding

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A Milling Machine without the tooling would be a fairly useless machine tool. It is the vast amount of tool holders and accessories that go along with the milling machine that expands the uses for this machine. This section is entitled Tool Holding . In tool holding we try to include the most common types of tool holding methods.
There are two basic types of collets used on milling machines. The solid collet and the split collet (Figure 1 & 2).

  Figure 1

Figure 2

Solid Collets- The solid collet is the most rigid type of tool holding collet. The solid type of collet is commonly referred to as an endmill holder. The solid type of collet has a precision ground shank which fits precisely into the spindle of the machine. The collet is held in the machine using a draw-in bolt which runs through the center of the spindle (Figure 3).

Figure 3

The solid collet also has a precision ground hole in it to accept the shank of the cutter. The cutter, in a solid collet, is secured using a set screw(s) (Figure 1). The set screw is tightened down on top of the flat which is ground or cast into the shank of the tool. Solid collets are used were the cutting forces might cause the tool to slip in a less rigid type of tool holder. Typical applications for solid collets would be indexable carbide endmilling and form cutting using a form relief cutter such as a t-slot or dovetail cutter. Solid collets come in many different sizes. Each size is precision ground to accept different size cutters and tool holder shanks.

Split Collets-Split collets are very popular on vertical milling machines. On the type of split collet shown in Figure 2, the tapered neck of the split collet is pulled into the spindle taper of the machine using the draw bar or draw bolt on the machine spindle. The pulling in of the collet causes the split collet to squeeze down onto the tool shank. Split collets are a very effective tool holding method, although under heavy cutting pressures split collets may have a tendency to slip. Another type of split collet system where the tool slippage may be minimized is the collet chuck system (Figure 4).

Figure 4

The collet chuck system uses a split type collet commonly referred to as a spring collet. The collet chuck adapter is machined to accept the spring collet. As the nosepiece for the collet chuck is tightened the collet clamps down onto the tool shank. Some collet chuck systems utilize a non-pull out button which aligns with the flat on the tool shank to prevent slippage (Figure 5).

Figure 5

It is important to note that when using the collet chuck system, snap the collet into the nosepiece first before placing the tool and the collet into the body of the collet chuck (figure 6). Failure to assemble the collet chuck in the proper order can cause serious damage to the collet and the chuck.

Figure 6

Shell End Mill Adapter-
Face milling cutters under six inches are known as shell end mills (Figure 7). Shell end mills come in different cutting tool materials. Carbide and high speed steel being the most common.

Figure 7

To use the shell end mill, it has to be attached to an adapter before it can be mounted in the machine spindle. The adapter (Figure 8)holds the milling cutter in place through the use of a clamp screw. Drive keys mounted in the adapter align with keyways formed in the shell end mill and are used to drive the cutter. The shell end mill and the adapter are aligned through the use of a large counter bore on the back of the cutter and a precision ground pilot on the nose of the adapter.

Figure 8