A key advantage of owning a lathe is the ability to machine threads. While taps and dies can cut many threads, acquiring a comprehensive tap and die set to cover all non-standard thread sizes can be costly. Sherline provides a unique and versatile thread-cutting attachment for its lathe. This affordable attachment enables you to machine thirty-six different unified thread pitches (ranging from 80 to 5 threads per inch) and twenty-eight different metric thread pitches (ranging from .25 to 2.0 mm). It also allows for both left-hand and right-hand threading. A 60° carbide cutting tool is included, but you can also grind a standard high-speed steel tool to cut various thread forms at any pitch diameter. This versatility allows you to machine both standard and non-standard inside or outside threads, as long as they fall within the lathe’s size limitations.

Note: Ensure you lubricate the gears with light oil before using the threading attachment.

The attachment includes:

• 15 aluminum gears
• Mounting brackets
• Engagement mechanism
• 4.00" (102 mm) handwheel

Thread cutting on the Sherline lathe is accomplished by gearing the spindle to the leadscrew. As the spindle is rotated using the handwheel mounted on the headstock spindle, the tool advances according to the gear ratio. Once the tool reaches the end of its movement, simply stop cranking, reverse the tool, and turn the spindle in the opposite direction until the tool passes its starting point. Reset the tool, and you’re ready for the next pass. It’s as straightforward as tapping! By using the supplied 127-tooth gear, you can cut true metric threads on an inch lathe or true inch threads on a metric lathe.

⚠️ Note: The thread-cutting attachment is not compatible with the 3C Headstock.

Adapting the Leadscrew Engagement Lever for Use with Digital Readout (DRO)

Gear Selection Calculator

The Sherline Thread Attachment Calculator, created by Joo Beng Koh of Singapore, automates gear selection based on your desired thread count. Originally shared on the Sherline Lathe & Mill Facebook Group, Joo Beng graciously allowed us to feature this tool on our website. The calculator simplifies the setup process, particularly for users who frequently change their thread specifications.

For instructions, select the desired parameters in the light yellow fields, and the corresponding gear selections will appear in the green boxes. An accompanying image shows the correct gear placement along with step-by-step guidance for installation. This tool has greatly improved the process for Joo Beng and can help others as well.