Thread Cutting Attachment

Thread Cutting Attachment (Lathe not included)

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.

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 he has 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

31010 Handwheel
31020 Primary Support Arm
31030 Secondary Support Arm
31040 Small Shim Washer
31050 Large Shim Washer (2)
31060 Gear Bushing (2)
31070 Gear Drive Pin
31080 10/32 X 3/8″ Set Screw
31090 Sheet Metal Screw, Pan Head, No. 6 X 3/16″, Type A
31100 100 Tooth Gear, 56 Pitch (W/ Notch)
31110 100 Tooth Gear, 56 Pitch
40340 10-32 X 1″ Skt Hd Cap Screw
40510 10-32 X 3/8″ Skt Hd Cap Screw (3)
40330 10-32 X 5/8″ Skt Hd Cap Screw
40660 No. 10 Washer
31150 Gear Shaft (2)
31200 20 Tooth Gear, 24 Pitch (2)
31220 22 Tooth Gear, 24 Pitch
31240 24 Tooth Gear, 24 Pitch
31260 26 Tooth Gear, 24 Pitch
31270 127 Tooth Gear, 56 Pitch
31280 28 Tooth Gear, 24 Pitch
31300 30 Tooth Gear, 24 Pitch
31320 32 Tooth Gear, 24 Pitch
31340 34 Tooth Gear, 24 Pitch
31360 36 Tooth Gear, 24 Pitch
31380 38 Tooth Gear, 24 Pitch
31400 40 Tooth Gear, 24 Pitch
31500 50 Tooth Gear, 56 Pitch
15090 Sliding Shaft
15410 Sliding Shaft O-Ring
15420 Engagement Lever
15430 Fixed Shaft
40900 10-32 x 3/8″ Flat Head Socket Screw

Optional 24 Pitch gears are available for cutting odd numbers of T.P.I., where the last two numbers before the final zero(s) in the part number represent the number of gear teeth. Available are sizes 31210, 31230, 31250, 312700, 31290, 31310, 31330, 31350, 31370 and 31390.

Assembling the Thread Cutting Attachment

Using the Threading Cutting Attachment


Cutting Threads with the Compound Slide