Turning Tools

Radius/Ball Turning on a Lathe

Single-Point Cutting Tool Geometry & Clearance

• A Single-Point Cutting Tool is a metalworking tool that is used in lathes to remove material from a workpiece. As the name suggests, these tools have only one cutting edge, which is used to create chips by removing material from the workpiece in a controlled manner.

• Single-point cutting tools work by rotating against the workpiece and making contact with it at a specific angle. As the tool moves along the workpiece, it removes material through a process called cutting. The cutting action generates heat and can cause wear on the tool, which is why tool geometry is so important.

• The geometry of a single-point cutting tool includes several critical angles, including the rake angle, relief angle, and clearance angle. These angles determine how the tool interacts with the workpiece and how effectively it can remove material:

  • Rake Angle is the angle between the top surface of the cutting tool and the surface being cut. A positive rake angle means that the tool is angled in the direction of the cut, which makes it easier to remove material but also creates more heat and friction. A negative rake angle means that the tool is angled away from the direction of the cut, which makes it more difficult to remove material but generates less heat and friction.

  • Relief Angle is the angle between the cutting edge and the surface of the tool behind the cutting edge. This angle is important because it allows chips to flow freely away from the cutting edge, preventing them from getting in the way of the cutting action.

  • Clearance Angle is the angle between the side of the cutting tool and the surface being cut. This angle ensures that the tool doesn't rub against the workpiece, which can cause wear and tear on the tool and reduce its effectiveness.

• The geometry of a single-point cutting tool is critical because it determines how effectively the tool can remove material and how long it will last before needing to be replaced. By selecting the right tool geometry for a specific part feature, machinists can achieve the desired results with minimal wear and tear on the tool.

Grinding a HSS Tool

• • Making a custom turning/form tool for use in a lathe is a handy skill to have when all you have access to is a manual lathe and you need to precisely cut non-standard features into a part. To make a custom tool, follow these steps:

    • Select a High-Speed-Steel (HSS) Blank: Choose a high-speed-steel blank that is appropriate for the size and shape of the tool you want to create. High-speed-steel is a type of steel that can withstand high temperatures and is ideal for cutting tools.

    • Layout: Using a scribe or other marking tool, layout the desired shape of the tool on the surface of the blank. This will serve as a guide when grinding the tool.

    • Rough Grind: Using a bench grinder or other grinding tool, grind the blank to the desired shape and size. Start with a rough grind to remove most of the material and then gradually work towards the final shape. Make sure to keep the tool cool while grinding to avoid overheating and damaging the steel.

    • Finish Grind/Polish: After the rough grinding is done, use a tool post grinder or other precision grinding tool to achieve the final shape and surface finish. The tool must be ground to the correct angles, including the rake angle, relief angle, and clearance angle, to ensure optimal cutting performance. Finally, polish the cutting edge to achieve a sharp edge.

    • Test Cut: Once the tool is finished, it should be tested on a workpiece to ensure that it is cutting as desired. Make sure to adjust the cutting parameters, such as cutting speed and feed rate, to achieve the best results.

  • Making a custom turning/form tool requires precision grinding skills and an understanding of the specific requirements of the tool. Machinists must have a good understanding of the material being cut, the tool geometry, and the desired results to create an effective cutting tool.