"

9.6 Tool Holding

Micky R. Jennings

Tool holding devices on a milling machine are designed to securely hold the tools for various operations. They need to be simple, quick, and easy to use. The most common tool holding solutions on milling machines are drill chucks and collets. These solutions come in many different styles, but they all perform the same function of holding the tools. Not all tool holding devices are right for every job though.  Drill chucks are only used to hold the hole making tools outlined in the drill press chapter. Tools that cut in a lateral motion require more support than a drill chuck can provide.

End Mill Holder

An end mill holder with an integral R8 taper.
Figure 9.87. An end mill holder with an integral R8 taper. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
A close up view of an endmill holder focussing on the bore to which an end mill is inserted and the set screws that would secure the end mill.
Figure 9.88. A close-up view of an endmill holder showing the bore to which an end mill is inserted, and the set screws that secure the end mill. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
An end mill holder with a ball end mill installed.
Figure 9.89. An end mill holder with a ball end mill installed. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
A close up view of the shank of a milling tool that has setscrew flats for securing in an endmill holder.
Figure 9.90. A close-up view of the shank of a milling tool that has set screw flats for securing in an endmill holder. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0

An end mill holder is a solid R8 tapered holder that has a set screw for securing an end mill or other side cutting tool. In addition to the precision taper, there is also a precision diameter. These features mate against or inside the precisely ground spindle. The holder also has a thread in the end to tighten the tool into the spindle.

Spring Collet

Three spring collets sit on a piece of plywood on top of a milling table.
Figure 9.91. Three spring collets sit on a piece of plywood on top of a milling table. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
Two spring collets laying on a table showing the standard range of R8 collets. To the left is a ¾
Figure 9.92. Two spring collets lay on a table showing the standard range of R8 collets. To the left is a ¾” collet, and to the right is a â…›” collet. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
The side profile of a spring collet showing the R8 taper, precision upper diameter, pin slot, and one of the compression slits.
Figure 9.93. The side profile of a spring collet showing the R8 taper, precision upper diameter, pin slot, and one of the compression slits. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
A close up view of the thread in the end of a spring collet.
Figure 9.94. A close-up view of the thread in the end of a spring collet. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0

A spring collet, often just called a collet, also has an R8 taper, a precision diameter, and a thread in the end. However, these holders are not solid; they are flexible. The collets use this flexibility to clamp onto the tool as the drawbar pulls the collet up into the taper of the spindle. Collets are not designed to grip on diameters larger or smaller than the advertised size. Doing so could damage the tooling and the collet or allow the cutting tool to slip during the machining process.

Draw Bar

Side view of a draw bar showing the thread, shaft, shoulder, and hex.
Figure 9.95. Side view of a draw bar showing the thread, shaft, shoulder, and hex. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
A close up view of the threads at the end of a draw bar.
Figure 9.96. A close-up view of the threads at the end of a draw bar. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
An exploded view of a draw bar, collet, and tool and their relationship as installed in the milling machine.
Figure 9.97. An exploded view of a draw bar, collet, and tool and their relationship as installed in the milling machine. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
A close up view of the working relationship between draw bar, collet, and tool.
Figure 9.98. A close-up view of the working relationship between draw bar, collet, and tool. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0
An end of tool view of the working relationship between draw bar, collet, and tool.
Figure 9.99. An end of tool view of the working relationship between draw bar, collet, and tool. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0

A draw bar is a long rod that has a head with a hex on one end and threads on the other. The draw bar sits inside the spindle, and the larger diameter head rests against the top. The threaded end of the draw bar is used to screw into the ends of various tool holders that may be inserted into the spindle. As the draw bar is tightened, the tool holder gets pulled further into the spindle and increases the engagement of the R8 taper, locking it in position.

Drill Chuck

A keyless drill chuck. A straight shank with a flat is used for holding the chuck in a collet or an end mill holder.
Figure 9.100. A keyless drill chuck. A straight shank with a flat is used for holding the chuck in a collet or an end mill holder. / Image Credit: Micky R. Jennings, courtesy of Wenatchee Valley College, CC BY 4.0

A drill chuck for milling machines can be similar to those of the drill press but is often of better quality and may be of the keyless variety. Keyless chucks have a couple advantages over keyed chucks. The first is that they are easy to use and require only hand strength to tighten. The second is that if they start to slip, the internal mechanism will twist, tightening the chuck and stopping the slipping action. One thing to note is that drill chucks are only for holding plunging style tools that are capable of stabilizing themselves. End mills and all other side cutting tools cannot be held securely in a drill chuck.

Attributions

  1. Figure 9.87: End mill holder by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  2. Figure 9.88: End mill holder 2 by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  3. Figure 9.89: End mill holder with tool by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  4. Figure 9.90: Setscrew flats by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  5. Figure 9.91: Three spring collets by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  6. Figure 9.92: Two spring collets by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  7. Figure 9.93: Spring collet by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  8. Figure 9.94: Spring collet thread by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  9. Figure 9.95: Draw bar by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  10. Figure 9.96: Draw bar threads by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  11. Figure 9.97: Draw bar, collet, and tool by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  12. Figure 9.98: Draw bar, collet, and tool 2 by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  13. Figure 9.99: Draw bar, collet, and tool 3 by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
  14. Figure 9.100: Keyless drill chuck by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
definition

License

Icon for the Creative Commons Attribution 4.0 International License

Introduction to Machining Copyright © by SBCTC is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book