10.6 Tool Holding
Micky R. Jennings
Workholding devices on a lathe 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 a lathe are tool posts and drill chucks. These solutions come in many different styles, but they perform the same function of holding the tools.
Rocker Tool Post
Arocker tool post is one of the older styles of tool posts that may still be found on some lathes. This style has a central bolt that tightens against a tool holder. The tool holder itself is sitting on a wedge that has a round bottom. The round bottom of the wedge sits in a round tapered base. The circular portion of the wedge and the base allow the tool holder to rock up and down. The up-and-down movement is used to set the tool height before locking the tool into position with the top bolt.
Square Indexable Tool Post
A square tool post has a central bolt and nut arrangement that tightens it to the tee slot in the compound rest. Tools can be mounted on four sides of this tool post and indexed when loosened in order to use different cutting tools. When tools are mounted in this tool post, they must be shimmed in order to get the proper tool height. This tool post design is still seen on some lathes but in many instances, it has been replaced with a more efficient model.
Quick Change Tool Post
Quick change tool posts have become the standard in the industry. With a design that is quick, easy to use, and repeatable, it is superior to many other styles. Although there are many different types of quick change tooling some common elements exist. Quick change tool holders have a central bolt and nut, similar to the square type, locking in the position and orientation of the main body of the tool post. There is a cam mechanism inside the base that is actuated by a handle on top of the tool post. The cam mechanism moves a piston or a portion of a dovetail in and out to tighten and loosen a tool holder that is mounted onto the body. The tool holder itself has a similar design to that of the square tool post, using set screws to tighten a cutting tool inside a support channel. The difference is that the tool holder has an adjustable screw that is used to move the tool holder up and down on the body before it is secured in place. This system allows the operator to have as many different tools as they have tool holders available. In fact, the operator can save time by setting the tools up once rather than adjusting and setting the tools up for each part.
Drill Chuck
A drill chuckis a complex device that uses multiple jaws to grip on the straight shanks of drilling style cutting tools. As the outer collar of the chuck is rotated, either by hand or by chuck key, the jaws synchronously close on the cutting tool, gripping it with a high level of concentricity. The interior components of a drill chuck have many ground precision surfaces in order for this to work correctly. Low quality, or worn chucks, may have tool runout that is unacceptable for some operations. Modern drill chucks may be keyed or keyless. Keyless chucks are becoming popular on machine tools because of their ease of use and quick tool changing capabilities. In order to use a keyless chuck, the operator just needs to grip the outer portion of the chuck in one hand and the upper knurled ring in the other and twist. Hand tight is all that is needed. Because of the way keyless chucks are designed, if the tool starts to slip, it will twist the jaws and outer portion of the chuck and give the chuck a tighter grip to stop the slipping.
Morse Taper
Morse tapers are considered self-holding tapers and are suitable on a lot of manual machinery in a shop. The Morse taper holds tools in alignment by a tight wedging action of both parts of the mating tapers. Often, the Morse taper will have a flattened portion at the end, known as a tang. The tang is for alignment and removal of the tool. Morse tapers are a suitable tool holding method on lathes for drilling style operations that have a twisting force and forces pushing into the quill of the tailstock. They are not a good choice for sideways force as this could loosen the taper and dislodge the tool.
Attributions
- Figure 10.57: Square tool post by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.58: Quick change tool post by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.59: Quick change tool post 2 by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.60: Quick change tool post 3 by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.61: Quick change tool holders by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Video 10.23: Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.62: Keyless drill chuck by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 10.63: Morse taper by Micky R. Jennings, courtesy of Wenatchee Valley College, for WA Open ProfTech, © SBCTC, CC BY 4.0
An antiquated style of tool holding device that uses a rocking motion to position the height of the tool.
A tool holding device that is capable of holding multiple tools as well as the ability to easily cycle between them.
A modern standard in tool holding. Allows the operator to quickly and repeatedly change tools during the machining process.
A device used to easily hold hole making tools.
