A Complete Guide to Effective Screw Thread Machining

A complete guide to effective screw thread machining

August 1, 2025
By Sandvik Coromant, for the Blue Print

Threading might seem straightforward — just cutting a groove around a cylinder, right? But there’s far more nuance involved in creating strong, accurate threads that deliver the right fit and function. From engine components to heavy-duty fasteners, threaded parts are found almost everywhere. To guarantee reliable performance, the threading process requires careful attention. Here’s a quick, approachable look at how to optimize thread turning for both precision and efficiency.

Theory

In thread turning, a threading insert is typically used to create the thread profile and pitch required. An indexable insert tool uses a program to help create the thread by breaking down the total depth into smaller passes until you reach the threading specifications. By gradually working down to the final cutting depth, you minimize stress on the delicate thread-profile point of the cutting edge. This approach helps preserve tool integrity, extend cutting life, and maintain thread accuracy—even in high-volume or high-hardness applications. Different infeed methods perform better depending on the pitch and the material being threaded. Many times, you will see Radial infeed still used because it's what has been a standard for many years. We recommend using a modified flank infeed to achieve more consistent threading tool life and improved chip control.

Selection procedure

To get started, nail down these key parameters:

Thread Type and Pitch: Are you cutting metric threads, imperial threads, or something more specialized like trapezoidal or ACME? Identifying the exact profile and pitch is your first step in selection.
Material Characteristics: Steel, aluminum, and exotic alloys each require different insert grades and cutting strategies. Harder materials typically call for tougher inserts with heat-resistant coatings.
Cutting Depth and Passes: Determine how many passes are needed to remove material in small increments without overloading the tool. This can also impact cycle time and tool wear.

System overview

Successful thread turning depends on the entire machining ecosystem:

Machine Rigidity: Any vibration or chatter can quickly compromise thread quality.
Tooling: From indexable inserts to toolholders, a stable setup ensures the cutting edge remains properly aligned. Choosing the appropriate shim to give your threading insert with the best inclination clearance on both flanks is a commonly overlooked detail.
Programming: Consistent feeds and speeds, combined with correct toolpath positioning, are critical for achieving the final form.
Coolant/Lubrication: Keeping the cutting zone cool and effectively clearing chips away helps prevent re-cutting, which can degrade both the insert and the part’s surface.

How to apply

Set Up: Begin by confirming your toolholder is properly squared and at the correct angle for your thread form.
Program Passes: Configure multiple passes in your CNC program - or carefully plan them for a manual lathe - to gradually deepen the thread groove. Programming with a different number of passes can give you improved results and can be done easily with most modern canned software.
Monitor Cutting: Pay close attention to chip formation and surface finish on the threads. Catching issues early can help avoid expensive rework later.

Troubleshooting

Chatter or Vibration: This often points to insufficient machine rigidity or an improperly seated insert. Adjust feeds and speeds, check your clamping setup, and ensure the correct inclination angle to allow free cutting.
Premature Insert Wear: May indicate the need for a different insert grade or better coolant application.
Inaccurate Threads: Verify that your tool is correctly oriented and that your machine is programmed for the precise thread pitch and depth.

Tapping

Although thread turning gets most of the spotlight, tapping is another common approach for creating internal threads. Instead of a single-point cutting edge, tapping relies on specialized taps with multiple edges. This method can be faster for smaller diameters but also requires carefully selected taps and matched speeds to avoid breakage or galling. For deeper or larger-diameter holes, thread turning or thread milling often provides better control and improved surface quality.

Threading may be a classic machining process, but as with any craft - the smallest details matter. By choosing the right insert, cutting parameters, and machine settings, you can produce threads that perform consistently - whether they’re destined for assembly on the shop floor or high-stress applications in aerospace. The key is to plan carefully, closely monitor your process, and be ready to adjust as you go. With a solid approach and a bit of know-how, you’ll be well on your way to mastering precision threading.

Content originally from Sandvik Coromant. Reused here with permission.