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Confidently Select Your Next Thread Mill

Do you know the key differences between a Single Form Thread Mill and a Multi-Form Thread Mill? Do you know which tooling option is best for your job? This blog post examines how several factors, including the tool’s form and max depth of thread, are important to ultimately making the appropriate Harvey Tool thread mill decision.

Thread Mill Product Offering

Single Form Thread Mill

The single form thread mill is the most versatile threading solution Harvey Tool offers. These tools are ground to a sharp point and are capable of milling 60° thread styles, such as UN, metric, and NPT threads. With over 14 UN and 10 Metric sized tools, Harvey Tool’s single form selections allow machinists the opportunity to machine many different types of threads.

Thread Mill

Harvey Performance Company, LLC.

Single Form Thread Mills for Hardened Steels

Similar to the standard single form thread mills, Harvey Tool’s thread mills for hardened steels offer machinists a quality option when dealing with hardened steels from 46-68 Rc. The following unique geometries helps this tool machine tough alloys:

  1. Ground Flat – Instead of a sharp point these tools have a ground flat to help ensure long tool life.
  2. Eccentric Relief – Gives the cutting edges extra strength for the high feeds at relatively low RPMs required for harder materials.
  3. AlTiN Nano Coating – Allows for superior heat resistance.
thread mill

Harvey Performance Company, LLC.

A key difference between the standard Single Form Thread Mill and the Single Form Thread Mills for Hardened Steels is that the thread mills for hardened steels are actually only capable of milling 83% of the actual thread depth. At first, this may seem detrimental to your operation. However, according to the Machinery’s Handbook 29th Edition, “Tests have shown that any increase in the percentage of full thread over 60% does not significantly increase the strength of the thread. Often, a 55% to 60% thread is satisfactory, although 75% threads are commonly used to provide an extra margin of safety.” With the ability to preserve tool life and effectively perform thread components, Harvey Tool’s single form thread mills for hardened steels are a natural choice when tackling a hardened material.

Tri-Form Thread Mills

Tri-Form thread mills are designed for difficult-to-machine materials. The tri-form design reduces tool pressure and deflection, which results in more accurate threading. Its left-hand cut, left-hand spiral design allows it to climb mill from the top of the thread to the bottom.

thread mill

Harvey Performance Company, LLC.

Multi-Form Thread Mills

Our multi-form thread mills are offered in styles such as UN, NPT, and Metric. Multi-Form Thread Mills are optimized to produce a full thread in single helical interpolation. Additionally, they allow a machinist to quickly turn around production-style jobs.

thread mill

Harvey Performance Company, LLC.

Coolant-Through Multi Form Thread Mills

Coolant-Through Multi Form Thread Mills are the perfect tool for when a job calls for thread milling in a blind hole. The coolant through ability of the tool produces superior chip evacuation. These tools also improve coolant flow to the workpiece – delivering it directly from the tip of the tool – for decreased friction and high cutting speeds.

thread mill

Harvey Performance Company, LLC.

Long Flute Thread Mills

These tools are great when a job calls for a deep thread, due to their long flute. Long Flute Thread Mills also have a large cutter diameter and core, which provides the tool with improved tool strength and stability.

thread mill

Harvey Performance Company, LLC.

N.P.T. Multi-Form Thread Mills

While it may seem obvious, N.P.T. Multi-Form Thread Mills are perfect for milling NPT threads. NPT threads are great for when a part requires a full seal, different from traditional threads that hold pieces together without the water-tight seal.

thread mill

Harvey Performance Company, LLC.

Understanding Threads & Thread Mills

Thread milling can present a machinist many challenges. While thread mills are capable of producing threads with relative ease, there are a lot of considerations that machinists must make prior to beginning the job in order to gain consistent results. To conceptualize these features and choose the right tool, machinists must first understand basic thread milling applications.

 

What is a thread?

The primary function of a thread is to form a coupling between two different mechanisms. Think of the cap on your water bottle. The cap couples with the top of the bottle in order to create a water tight seal. This coupling can transmit motion and help to obtain mechanical advantages.  Below are some important terms to know in order to understand threads.

Root – That surface of the thread which joins the flanks of adjacent thread forms and is immediately adjacent to the cylinder or cone from which the thread projects.

Flank – The flank of a thread is either surface connecting the crest with the root. The flank surface intersection with an axial plane is theoretically a straight line.

Crest – This is that surface of a thread which joins the flanks of the thread and is farthest from the cylinder or cone from which the thread projects.

Pitch – The pitch of a thread having uniform spacing is the distance measured parallelwith its axis between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis. Pitch is equal to the lead divided by the number of thread starts.

Major Diameter – On a straight thread the major diameter is that of the major cylinder.On a taper thread the major diameter at a given position on the thread axis is that of the major cone at that position.

Minor Diameter – On a straight thread the minor diameter is that of the minor cylinder. On a taper thread the minor diameter at a given position on the thread axis is that of the minor cone at that position.

Helix Angle – On a straight thread, the helix angle is the angle made by the helix of the thread and its relation to the thread axis. On a taper thread, the helix angle at a given axial position is the angle made by the conical spiral of the thread with the axis of the thread. The helix angle is the complement of the lead angle.

Depth of Thread Engagement – The depth (or height) of thread engagement between two coaxially assembled mating threads is the radial distance by which their thread forms overlap each other.

External Thread – A thread on a cylindrical or conical external surface.

Internal Thread – A thread on a cylindrical or conical internal surface.

Class of Thread – The class of a thread is an alphanumerical designation to indicate the standard grade of tolerance and allowance specified for a thread.

Source: Machinery’s Handbook 29th Edition

Types of Threads & Their Common Applications:

ISO Metric, American UN: This thread type is used for general purposes, including for screws. Features a 60° thread form.

British Standard, Whitworth: This thread form includes a 55° thread form and is often used when a water tight seal is needed.

NPT: Meaning National Pipe Tapered, this thread, like the Whitworth Thread Form, is also internal. See the above video for an example of an NPT thread.

UNJ, MJ: This type of thread is often used in the Aerospace industry and features a radius at the root of the thread.

ACME, Trapezoidal: ACME threads are screw thread profiles that feature a trapezoidal outline, and are most commonly used for power screws.

Buttress Threads: Designed for applications that involve particularly high stresses along the thread axis in one direction. The thread angle on these threads is 45° with a perpendicular flat on the front or “load resisting face.”         

Thread Designations

Threads must hold certain tolerances, known as thread designations, in order to join together properly. International standards have been developed for threads. Below are examples of Metric, UN, and Acme Thread Designations. It is important to note that not all designations will be uniform, as some tolerances will include diameter tolerances while others will include class of fit.

Metric Thread Designations              

M12 x 1.75 – 4h – LH

In this scenario, “M” designates a Metric Thread Designation, 12 refers to the Nominal Diameter, 1.75 is the pitch, 4h is the “Class of Fit,” and “LH” means “Left-Hand.”

UN Thread Designations

¾ 10 UNC 2A LH

For this UN Thread Designation, ¾ refers to the thread’s major diameter, where 10 references the number of threads per inch. UNC stands for the thread series; and 2A means the class of thread. The “A” is used to designate external threads, while “B” is for internal threads. For these style threads, there are 6 other classes of fit; 1B, 2B, and 3B for internal threads; and 1A, 2A, and 3A for external threads.

ACME Thread Designations

A 1 025 20-X

For this ACME Thread Designation, A refers to “Acme,” while 1 is the number of thread starts. The basic major diameter is called out by 025 (Meaning 1/4”) while 20 is the callout for number of threads per inch. X is a placeholder for a number designating the purpose of the thread. A number 1 means it’s for a screw, while 2 means it’s for a nut, and 3 refers to a flange.

How are threads measured?

Threads are measured using go and no-go gauges. These gauges are inspection tools used to ensure the that the thread is the right size and has the correct pitch. The go gauge ensures the pitch diameter falls below the maximum requirement, while the no-go gauge verifies that the pitch diameter is above the minimum requirement. These gauges must be used carefully to ensure that the threads are not damaged.

Thread Milling Considerations

Thread milling is the interpolation of a thread mill around or inside a workpiece to create a desired thread form on a workpiece. Multiple radial passes during milling offer good chip control. Remember, though, that thread milling needs to be performed on machines capable of moving on the X, Y, and Z axis simultaneously.

5 Tips for Successful Thread Milling Operations:

1.  Opt for a Quality Tooling Manufacturer

There is no substitute for adequate tooling. To avoid tool failure and machining mishaps, opt for a quality manufacturer for High Performance Drills for your starter holes, as well as for your thread milling solutions. Harvey Tool fully stocks several types of threadmills, including Single Form, Tri-Form, and Multi-Form Thread Milling Cutters. In addition, the 60° Double Angle Shank Cutter can be used for thread milling.

thread milling

Image Courtesy of  @Avantmfg

2. Select a Proper Cutter Diameter

Choose only a cutter diameter as large as you need. A smaller cutter diameter will help achieve higher quality threads.

3. Ensure You’re Comfortable with Your Tool Path

Your chosen tool path will determine left hand or right hand threads.

Right-hand internal thread milling is where cutters move counterclockwise in an upwards direction to ensure that climb milling is achieved.

Left-hand internal thread milling a left-hand thread follows in the opposite direction, from top to bottom, also in a counterclockwise path to ensure that climb milling is achieved.

4. Assess Number of Radial Passes Needed

In difficult applications, using more passes may be necessary to achieve desired quality. Separating the thread milling operation into several radial passes achieves a finer quality of thread and improves security against tool breakage in difficult materials. In addition, thread milling with several radial passes also improves thread tolerance due to reduced tool deflection. This gives greater security in long overhangs and unstable conditions.

5. Review Chip Evacuation Strategy

Are you taking the necessary steps to avoid chip recutting due to inefficient chip evacuation? If not, your thread may fall out of tolerance. Opt for a strategy that includes coolant, lubricant, and tool retractions.

In Summary

Just looking at a threading tool can be confusing – it is sometimes hard to conceptualize how these tools are able to get the job done. But with proper understanding of call, methods, and best practices, machinists can feel confident when beginning their operation.

6 Uses of Double Angle Shank Cutters

A Double Angle Shank Cutter is often referred to as the “Swiss Army Knife of Machining” due to its extreme versatility. This singular tool can be used for chamfering, back chamfering, V-groove milling, deburring, and countersinking. Below, we’ll learn the nuances of each operation, and why a Double Angle Shank Cutter might is an excellent tool to have on hand in any machine shop.


1. Thread Milling

Both in purpose and look, a Double Angle Shank Cutter is very similar to that of a single-form thread mill. Single-form thread mills are more versatile than multi-form thread mills, as they are not locked into a fixed pitch. Double Angle Shank Cutters that have a 60° angle can create internal and external 60° Unified National (UN) and metric threads. Double Angle Shank Cutters with a 55° angle can be used to thread 55° British Standard Pipe Threads (BSPT). To determine the thread sizes that various Double Angle Shank Cutters can produce, it’s helpful to consult thread fit charts, which pair appropriate cutter diameters to the thread size needed.


2. Chamfering

Depending on the requirements of your chamfering operation, and the angle of the chamfer you’re creating on your part, a Double Angle Shank Cutter might be appropriate. The angle of the top or bottom of the cutting face of the tool (called out below in as a B1 dimension), will determine the angle of your part’s chamfer. The area marked in red in Figures 2 and 3 below indicate the cutting portion for your chamfering and back chamfering (leaving a chamfer on the bottom of a part) operation.

For more information on the angles of Double Angle Shank Cutters, view Harvey Tool’s helpful guide: “Angles Untangled.”


3. Back Chamfering

Consider a through-hole that has a burr or tear-out caused from drilling the back of a workpiece. Reorienting the workpiece and relocating the hole is time-consuming, and it may be difficult to accurately finish the hole. In a case like this, back chamfering the burred hole without changing the setup is a preferred method. Put simply, the ability to accurately chamfer not only the top – but also the bottom of a part without needing to refasten the workpiece in your machine will save valuable time and money.

For best results when chamfering with Double Angle Shank Cutters, use a stepping over technique with diminishing passes as the radial engagement increases. This strategy helps to manage the amount of contact along the angle and can significantly avoid tool deflection.


4. Machining V-Grooves

A Double Angle Shank Cutter is commonly applied for machining V-groove profiles because of its cutting head, which is perpendicular to the tool centerline. This provides effective cutting action, even at a low spindle speed. A low tip speed can lead to issues with other tools, such as Chamfer Cutters, where the pointed profile is on-center of the tool.


5. Deburring

The task of hand-deburring parts can be tiresome for you, and cost inefficient for your shop. It can also lead to inaccuracies in parts that require precise dimensions. Double Angle Shank Cutters can be used to debur a part right in your CNC machine. By doing so, the process of finishing a part is made simple, fast, and accurate. Of course, ensuring proper clearance prior to machining the bottom of a machined hole is pivotal.

Other useful and versatile tools to have on-hand for quick CNC deburring include deburring end mills, back deburring mills, undercutting end mills, and chamfer cutters.


6. Countersinking

Countersinking a part  is done so a screw, nail, or bolt is able to sit flush with the part surface. Using specialty profile tooling can help enlarge the rim of a drilled hole and bevel the sides for a screw to sit accurately. A Double Angle Shank Cutter can also perform this operation by using the bottom portion of its cutting face.


Because of its ability to perform six different operations, Double Angle Shank Cutters are an ideal tool to keep in your tool carousel. In a bind, these tool forms can mill threads, chamfer, back chamfer, machine v-grooves, deburr in your CNC machine, and countersink. This versatility makes it a machining favorite and can offer shops boosted productivity by eliminating the need to flip parts, deburr by hand, or carry multiple tool forms.

For more on Harvey Tool Double Angle Shank Cutters, Click Here.

Multi-Start Thread Reference Guide

A multi-start thread consists of two or more intertwined threads running parallel to one another. Intertwining threads allow the lead distance of a thread to be increased without changing its pitch. A double start thread will have a lead distance double that of a single start thread of the same pitch, a triple start thread will have a lead distance three times longer than a single start thread of the same pitch, and so on.

By maintaining a constant pitch, the depth of the thread, measured from crest to root, will also remain constant. This allows multi-start threads to maintain a shallow thread depth relative to their longer lead distance. Another design advantage of a multi-start thread is that more contact surface is engaged in a single thread rotation. A common example is a cap on a plastic water bottle. The cap will screw on in one quick turn but because a multi start thread was used there are multiple threads fully engaged to securely hold the cap in place.

multi-start thread

Figure 1 displays a triple start thread with each thread represented in a different shade. The left side of the image represents a triple start thread with just one of the three threads completed. This unfinished view shows how each individual thread is milled at a specific lead distance before the part is indexed and the remaining threads are milled. The right side of the image displays the completed triple start thread with the front view showing how the start of each thread is evenly spaced. The starting points of a double start thread begin 180° apart and the starting points of a triple start thread begin 120° apart.

multi-start thread

Figure 2 displays the triangle that can be formed using the relationship between the lead distance and the circumference of a thread. It is this relationship that determines the lead angle of a thread. The lead angle is the helix angle of the thread based on the lead distance. A single start thread has a lead distance equal to its pitch and in turn has a relatively small lead angle. Multi-start threads have a longer lead distance and therefore a larger lead angle. The graphic depicted on the right is a view of the lead triangle if it were to be unwound to better visualize this lead angle. The dashed lines represent the lead angle of a single start thread and double start thread of the same pitch and circumference for comparison. The colors represent each of the three intertwined threads of the triple start thread depicted in Figure 1.

Lead Angle Formula

multi-start thread

The charts below display the information for all common UN/Metric threads as well as the lead and lead angle for double and triple start versions of each thread. The lead angle represented in the chart is a function of a thread’s lead and major diameter as seen in the equation above. It is important to be aware of this lead angle when manufacturing a multi-start thread. The cutting tool used to mill the thread must have a relief angle greater than the lead angle of the thread for clearance purposes. All Harvey Tool Single Form Thread Milling Cutters can mill a single, double, and triple start thread without interference.

Machining a Multi-Start Thread

  1. Use the table or equation to determine the pitch, lead, and lead angle of the multi-start thread.
  2. Use a single form thread mill to helically interpolate the first thread at the correct lead. *The thread mill used must have a relief angle greater than that of the multi-start thread’s lead angle in order to machine the thread.
  3. Index to the next starting location and mill the remaining parallel thread/threads.

Click here for the full chart – starting on Page 2.

multi-start thread