An In-Depth Pitch On Thread Milling - The Ultimate Guide!

January 16, 2023 By tyler welch

Thread milling has become an increasingly popular alternative to tapping and thread turning. Not only can thread milling cutters be extremely flexible and be used for many different applications, but it can be cost effective as well.

Read this in-depth pitch on thread milling to learn everything there is to know.

What is Thread Milling?

Thread milling is a metalworking operation used to cut internal and external threads of different sizes through the circular ramping movement of a rotating tool. The thread pitch is created by the lateral movement in one revolution. Different from tapping, thread milling is mainly applied to larger workpieces, however, solid carbide thread mills can also produce small threaded holes. The same tool can be used for both left and right-hand threads, different thread tolerance, various materials, and hole diameters, producing threads with high accuracy and great surface finish. Although not as widely used as thread turning, thread milling can achieve high productivity in some applications.

You're probably thinking, taps carry out the job faster, why is thread milling so big?

Read the next section and you will find out!

What are the benefits of Thread Milling?

Thread Milling provides a better quality thread than tapping as it offers better chip evacuation. Tapping uses a tool the same size as the thread, forcing the chip through the thread for evacuation.
Thread Milling tools are flexible. They can do internal and external threads, and can cut to different diameters, so long as the pitch is the same.
You can carry out threading in difficult to machine materials. Due to the superior cutting conditions, they can thread hardened steels up to HRC 65, Titanium and even more!
They are very secure due to producing short chips and having a low cutting force. The workpiece is less likely to get damaged as the diameter is smaller than the thread.
Using a tool smaller than the thread ensures the thread is properly machined with the correct clearance needed to evacuate the chips effectively.
One main advantage against tapping, is that tapping only starts making a complete thread profile on the third thread, whereas thread milling will produce a complete thread profile from the top to the bottom.
The process can reduce machining time and save energy.
High thread quality can be achieved without burrs.

What is a thread?

A thread is something we see and use everyday without even realising. Get thirsty? You unscrew your bottle lid to have a drink. That there, is a thread. Simply put, a thread forms a coupling between 2 different mechanisms. In this example, the bottle and the bottle lid form together to create a seal holding the water. Threads are measured using GO and NO-GO gauges. These measuring tools ensure the pitch is correct. The NO-GO gauge ensures the pitch diameter is above the minimum, and the Go gauge ensure it is below the maximum. There are other methods experienced engineers use to save the cost of a gauge, however gauges are the most reliable and efficient method.

What are all the types of thread mills?

MTD – 3 in 1 -Drill, Chamfer & Thread mill - Two fluted drill thread milling cutter with 45° chamfering. Ideal for mass production applications. High thread surface quality. Internal coolant. Optimized carbide grade for Aluminium and Cast Iron.
DMT – 3 in 1 - Drill, Chamfer & Thread mill - Short cycle time and high performance reduces machining costs. Suitable for both blind and through holes. Full Profile thread. No time lost for tool change, since drilling, chamfering and thread milling are done with one tool.
MTS – Mini Type - Can produce a wide range of threads and pitches and both External and Internal threads. Coolant-through the flutes is very effective for deep holes. Longer tool life due to special triple coating. Machining of hardened materials up to 45 HRc.
MTSB – Through Coolant Mini Type - Perfect for thread milling operations where chips are concentrated at the bottom of the thread and external coolant can’t wash the chips away or for complicated applications where external coolant is inefficient or can’t reach the machined area.
MTI – Single point mill thread. Same Tool for Internal and External Thread. Ultra-fine Sub-micron grade with PVD triple Blue coating on selected grades.
MT - Solid Thread Mills without internal coolant. Spiral flutes allow smooth cutting action. Shorter machining time due to multi, 3-6, flutes. Longer tool life due to special multi-layer coating. Excellent surface finish.
MTB – Through Coolant Thread Mills with internal coolant bore for blind holes. Spiral flutes allow smooth cutting action. Shorter machining time due to multi, 3 to 6, flutes. 2.2 mm and up cutting diameter. Longer tool life due to special multi-layer coating. Excellent surface finish.
MTZ – Through Flute Coolant Thread Mills. Spiral flutes allow smooth cutting action. Shorter machining time due to multi, 3 to 6, flutes. 2.2 mm and up cutting diameter. Longer tool life due to special multi-layer coating. Excellent surface finish.
MTQ – Long Reach Thread Mills that include relieved neck for deep work pieces. Spiral flutes allow smooth cutting action. Shorter machining time due to multi, 3 to 6, flutes. 2.2 mm and up cutting diameter. Longer tool life due to special multi-layer coating. Excellent surface finish.
FMT – Through Coolant (5-8 Flutes) - Fast Thread Mills with internal coolant bore. Spiral flutes allow smooth cutting action. Longer tool life due to special multi-layer coating. Excellent surface finish.
AMT - For aluminium - Optimized carbide grade for Aluminium, cast iron and stainless steels. Cylindrical shank (Weldon shank- upon request), with internal coolant bore. Uncoated, smooth cutting edge. High thread surface quality. Same tool for right hand or left hand internal threads.
SC – Solid carbide tapered end mill suitable for most materials. 4 Flute for effective chip evacuations. Offering an excellent surface finish.
Hard Type (H) – For hardened steels & super alloys (Hastelloy & Inconel, etc).
CMT – Thread, Groove, Rads, Chamfer, etc. - Solid carbide thread mills designed specifically for the machining of hardened materials up to 62HRc. These tools provide high performance, improved cut and an excellent surface finish. High temperature alloys. Titanium alloys. Super Alloys (Hastelloy, Inconel, Nickel Base Alloys).
SR – Standard indexable thread milling - Same toolholder and insert can produce both RH and LH threads. A single insert & toolholder can produce a given thread on many diameters (External & Internal). Most inserts are double sided, having two cutting edges. Longer tool life thanks to a special multilayer coating process.
SRH – Spiral mill thread - Spiral fluted toolholders hold 1 to 9 inserts in a comparatively small cutting diameter. The unique clamping method enables optimal indexability. This is a general purpose grade, which can be used with all materials.
D Thread – Extra long reach - Improved productivity due to multi-insert toolholders. Partial Profile, standard or U-type inserts for a wide range of threads. Inserts with three cutting edges, reduces tooling costs. Low cutting resistance due to the single point inserts.
Thread Whirling - Thread Whirling is a fast and accurate way to thread long, small diameter parts in exotic materials such as titanium, stainless steel and Inconel. Whirling inserts and holders can produce a wide range of medical parts such as dental implants and bone screws.
Bright - provides a smooth, polished finish on the tool. It increases chip flow in softer materials like aluminium.
Titanium Nitride (TiN) - is a multi-purpose coating which increases chip flow in softer materials. The heat and hardness resistance allows the tool to run at higher speeds than uncoated tools.
Titanium Carbonitride (TiCN) - is harder and more wear resistant than TiN. It is used on stainless steels, cast iron and aluminium alloys.
Aluminium Chromium Nitride (AlCrN) - has higher-heat resistance than AlTiN. It is commonly used for machining aircraft and aerospace materials, nickel alloys, stainless steel, titanium, cast iron and carbon steel.
TiCN PLUS Titanium Carbon-Nitride (TiCN) - plus Titanium Nitride (TiN) is an all-purpose finish designed to increase tool life by two to four times more than TiN coated tools. The heat and hardness resistance allows the tool to run at higher speeds than uncoated tools.

Solid Carbide VS Indexable

Most CNC milling machine operators will have different opinions on their preferred type of cutting tool for a specific application that is based strictly on past experience because it is natural to repeat strategies that have succeeded in the past. However, a better-educated decision can result in even better results. Walter Tools made a fantastic video explaining this.

To summarise, both types are very effective. However it all comes down to the job you’re carrying out. There are so many factors which come into play to picking the perfect tool. Hole diameter, workpiece material, size of the job, how many threads, cost effectiveness, cycle time of changing tools, and so many more. If you need help, please call us today and speak to our technician!

When to Use Thread Milling - Thread Milling Applications

Thin-walled parts
Asymmetric/non-rotating components
Machining materials generate high cutting force and easy to cause chip evacuation problems
Requiring to reduce tool inventory
Unstable component setups
As an alternative to tapping
Adjust the tolerance of the thread
Cut numerous odd thread sizes with a single tool
Back chamfer the hole

mts infographic

Thread Milling vs Tapping - What’s the Difference Between Thread Milling and Tapping?

Compared with tapping, which process should you choose?

Tapping is usually used to make threads in small holes after drilling, while thread milling tends to produce threads in larger holes.
Tapping uses a tool of the same size as the thread, forcing the chip through the thread to evacuate, while thread milling uses a tool with a smaller size than the thread, so thread milling achieves a better thread quality than tapping.
Tapping can be performed either by hand or machine. Thread milling usually requires CNC machine tools with at least three axes for helical interpolation.
Thread milling requires lower cutting forces than tapping.
It is not necessary to have the correct hole size in the thread milling process, a single tool can be used in thread milling to make a wide range of hole sizes. While for tapping, a different size tap is required for each size hole that needs to be threaded.
Thread milling produces pipe threads easily without creating the troublesome stringy chips produced in the tapping process.
Thread milling can achieve a better thread quality and smoother surface than tapping
Thread milling gives the user the ability to design custom threads, while the custom taps can be very expensive and require long lead times.
Tapping does not allow for adjusting the thread fit. Once the hole is tapped, the size and position of the thread are fixed. While the thread milling can control the fit. The machine operator has the ability to adjust thread size using a strategy similar to using an end mill, rather than a drill bit to make a hole.

Thread Milling Guide & Tips

1. Choose a proper quality tool

High-quality and suitable thread milling tool is essential to avoid failure and problems during the process, you can select some qualified tooling manufacturers and compare their advantages and disadvantages, and choose the one closest to your request. Before that, you need to master the types of thread mills (Helical flute thread mills, Straight flute thread mills, Single profile thread mills, Indexable insert thread mills, Solid carbide thread mills, etc.) and specifications of those thread milling cutters (Single form, Tri-form, and Multi-form), like diameters.

2. Apply several radial passes

Separate the thread milling operation into several radial passes can achieve higher quality, improve the thread tolerance, ensure safety and avoid tool breakage in difficult-to-machine materials, as well as make it suit in difficult applications, like long overhangs and unstable conditions.

3. Determine tool path

Left or right-hand threads are depending on the selected tool path. Which one is more suitable for you? Choose the more efficient one according to your experience.

4. Depth of the thread

Generally, the depth of the thread should be no more than one and a half times the diameter of the hole. Because the longer the milling tool, the more chance it can experience deflection, which can create inaccuracies in the thread.

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