Thread-Cutting Attachment


Out of stock

SKU: 3100 Category:

Product Description

About the Thread-Cutting Attachment

One of the big advantages of having a lathe is being able to machine threads. Many threads can be cut using taps and dies, but having a tap and die set that will enable you to cut all the non-standard thread sizes would be quite expensive. Sherline offers a unique and versatile thread-cutting attachment for its lathe. This low-cost attachment enables you to machine thirty-six different unified thread pitches (Pitch range from 80 to 5 threads per inch) and twenty-eight different metric thread pitches (Pitch range from .25 to 2.0 mm). It also allows you to cut them as either left-hand or right-hand threads. A 60° carbide cutting tool is included, but a standard high-speed steel lathe tool can be ground to cut various thread forms on any pitch diameter you desire. This versatility enables you to machine any inside or outside, standard or non-standard thread you might desire, as long as it is within the size limitations of the lathe.

NOTE: Lube up your gears well with light oil before using your threading attachment.

The attachment consists of:3100_thread-cutting_attachment_2

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

Threads are generated on the Sherline lathe by gearing the spindle to the leadscrew. As the spindle is rotated with the handwheel mounted on the headstock spindle, the tool will advance an amount determined by the ratio of the gears. When the tool has completed its movement, you simply stop cranking, back up the tool, and turn the spindle in the opposite direction until the tool is past its starting point. Then reset the tool, and you’re ready for the next pass. It’s as simple as tapping! By using a 127-tooth gear (supplied), true metric threads can be cut on an inch (model 4000, 4500, or 4400) or true inch threads on a metric (model 4100, 4530, or 4410) lathe.

NOTE: The thread-cutting attachment will work with all of our headstocks except the 3C Headstock (standard, ER16, and 9/16″).

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

If you are using the leadscrew engagement lever with the Thread Cutting Attachment in conjunction with Digital Readout (DRO), you will need to adapt your lathe with the DRO sliding shaft (sold separately) so the leadscrew engagement shafts will properly engage the leadscrew.

Gear Selection Calculator

This Sherline Thread Attachment Calculator comes to us via Joo Beng Koh of Singapore. He originally posted it to the Sherline Lathe & Mill Facebook Group and graciously allowed us to post his calculator link to our website. The calculator automates the gear selection based on the desired thread count.

Here is his explanation and a link to the spreadsheet calculator:

Click on the image for a larger view.

“I do use the Sherline Thread Attachment and found that it was quite tedious to set up the gears each time I wanted to cut threads. I didn’t use it that often, and the threads I cut often changed from project to project. So I created a spreadsheet on Google Sheets to “automate” the selection of the correct gears for the threads I wanted to cut. So I thought I’d share the spreadsheet in case others can also benefit from it. I hope it’s self-explanatory, but feedback to improve the sheet is certainly welcome. After selecting the parameters in light yellow, the “answers” will be shown in the green boxes. There is also an image on the right which shows which gears go where. There’s also a step-by-step description on the image to install the gears in the correct sequence. It made my life a lot easier, so hopefully, it’ll help some of you too!”

CLICK HERE for Joo Beng Koh’s Sherline Thread Attachment Calculator.

More Calculators

Visit our Calculators page to download or link to other Gear Tooth and Thread Calculators. The page includes calculators for thread counts, helical gears, conversions, etc.

The improper use of machine tools and their accessories can result in serious injury. Before using this tool, thoroughly read the instructions and make sure you understand its proper and safe use.


Always wear safety glasses when operating machine tools.

Download PDF 3100 Instructions

Instructions PDF Download

Download PDF Tip 92-Cutting Threads with the Sherline Compound Slide

Instructions PDF Download

Assembling the Thread Cutting Attachment

Using the Threading Cutting Attachment

Cutting Threads with the Compound Slide

Part No. Description Quantity
15090 Sliding Shaft 1
15410 Sliding Shaft O-Ring 1
15420 Engagement Lever 1
15430 Fixed Shaft 1
31010 Handwheel 1
31020 Primary Support Arm 1
31030 Secondary Support Arm 1
31040 Small Shim Washer 1
31050 Large Shim Washer 2
31060 Gear Bushing 2
31070 Gear Drive Pin 1
40520 10-32 x 3/16″ Set Screw 1
31090 4-40 x 3/16″ Pan Head Type F Thread Cutting Screw 1
31100 100 Tooth Gear, 56 Pitch (W/ Notch) 1
31110 100 Tooth Gear, 56 Pitch 1
31150 Gear Shaft 2
31200 20 Tooth Gear, 24 Pitch 2
31220 22 Tooth Gear, 24 Pitch 1
31240 24 Tooth Gear, 24 Pitch 1
31260 26 Tooth Gear, 24 Pitch 1
31270 127 Tooth Gear, 56 Pitch 1
31280 28 Tooth Gear, 24 Pitch 1
31300 30 Tooth Gear, 24 Pitch 1
31320 32 Tooth Gear, 24 Pitch 1
31340 34 Tooth Gear, 24 Pitch 1
31360 36 Tooth Gear, 24 Pitch 1
31380 38 Tooth Gear, 24 Pitch 1
31400 40 Tooth Gear, 24 Pitch 1
31500 50 Tooth Gear, 56 Pitch 1
40330 10-32 x 5/8″ SHCS 1
40340 10-32 x 1″ SHCS 1
40510 10-32 x 3/8″ SHCS 3
40660 #10 3/16″ Washer 1
40900 10-32 x 3/8″ Flat Head Socket Screw 1
21 Tooth Gear, 24 Pitch31210$19.64
23 Tooth Gear, 24 Pitch31230$19.64
25 Tooth Gear, 24 Pitch31250$19.64
27 Tooth Gear, 24 Pitch312700$19.64
29 Tooth Gear, 24 Pitch31290$19.64
31 Tooth Gear, 24 Pitch31310$19.64
33 Tooth Gear, 24 Pitch31330$19.64
35 Tooth Gear, 24 Pitch31350$15.90
37 Tooth Gear, 24 Pitch31370$19.64
39 Tooth Gear, 24 Pitch31390$19.64