PVD Coating vs. CVD: Two Common Coating Application Methods

Most tool manufacturers offer tool coatings, made up of a layer of metal compounds adhered to the surface of the tool to enhance its performance. The most common methods for adding coatings to a tool are Physical Vapor Deposition (PVD coating) and Chemical Vapor Deposition (CVD coating). This article will take a deep dive into each method to identify their unique and shared characteristics.

Physical Vapor Deposition (PVD) Coatings

The PVD coating method is a process in which metals go through a cycle of vaporization and condensation to be transferred from their original solid state to the tool. The metal compounds that make up the coatings are often referred to as the “metal material” in this process. The metal material starts as a solid wafer and is vaporized into a plasma, which can then be put onto the tools in the chamber. In this process, the tools are referred to as the “substrate.”

There are two different ways in which PVD coatings can be performed: arc ion plating and sputtering.

Arc Ion Plating & Sputtering

Key Differences

The main difference between arc ion plating and sputtering is that arc ion plating uses high electrical currents to vaporize the metallic material, and the metal ions are steered onto the tool for coating. Sputtering, in contrast, uses the properties of magnetic fields to direct reactive gasses to collide with a target made up of metallic material. During these collisions, metallic surface ions fall from the target and land on the substrate, slowly bombarding it until it is sufficiently coated. Both arc ion plating and sputtering are high temperature, ultrahigh vacuum processes. The term “vacuum” refers to any pressure below atmospheric pressure at sea level.

Above is an example of a Harvey Tool AlTiN Coated tool, which is applied using a PVD process.

Application Processes of Arc Ion Plating & Sputtering

Arc Ion Plating

  1. The internal pressure within the reaction chamber is dropped to form a vacuum to around 1 Pa (0.0000145 psi). Creating a vacuum is crucial as it removes any moisture and impurities, on or surrounding the tools.
  2. The chamber is heated to temperatures ranging from 150 – 750°C (302 – 1382°F). The temperature of the chamber is dependent on the coating that is being applied to create an ideal chemical reaction and adhesion between the plasma and substrate. A high current of around 100 A is applied to the metallic material causing an explosive reaction.
  3. The high current positively ionizes the metal and vaporizes it into a dense plasma.
  4. The substrate is negatively charged to attract the positive metal ions.
  5. The ions collide into tools with force and are deposited, forming a film that builds up in thickness to create the desired coating.

Sputtering

  1. The internal pressure within the reaction chamber is dropped to form a vacuum to around 1 Pa (0.0000145 psi) to remove any moisture and impurities on or surrounding the tools.
  2. An inert gas is pumped into the chamber to create a low pressure atmosphere. Inert gases are specifically used, as it is non-reactive with the metal elements and ensures that impurities are not mixed in with the tool coatings.
  3. The gas used is dependent on the atomic weight of the metal material; a heavier gas is commonly used with heavier metals.
  4. The chamber is heated to temperatures anywhere from 150 – 750°C (302 – 1382°F) depending on the coating that is being applied.
  5. The tools are placed between the metallic materials (called the “target” in sputtering) and an electromagnet, so that when turned on, a magnetic field runs along and around the tools.
  6. A high voltage is then applied along the magnetic field ionizing the argon atoms.
  7. Voltage ranges from 3-5 kV, and if using AC, with a frequency of around 14 MHz.
  8. The target is negatively charged attracting the positively charged Argon gas.
  9. The inert gas collides with the target ejecting metallic compounds onto the substrate to create a coating.

Key PVD Coating Differences, Summarized

Arc ion plating and sputtering are both effective methods of applying a PVD coating. So why use one over the other? Arc ion plating has a significantly higher ionization rate than sputtering, allowing for much faster deposition rates, shortening coating times. In turn, since sputtering is a slower process, it allows for more control when applying multi-metal compositions and ensuring that the stoichiometry of the coating is even throughout the tool. Finally, during the PVD coating process, micro-droplets are formed as the vaporized metals condense and solidify onto the tools. As these droplets impact the newly applied coating, they can cause defects and craters, producing residual stress points. In order to achieve a perfect coating, droplet size must be minimized. Arc ion plating produces droplets up to 3µm (micrometers) in diameter, while sputtering has droplets with diameters up to 0.3µm. With droplets up to ten times smaller, sputtering produces much smoother and defect-free surfaces which have been proven to slow corrosion rates.

Chemical Vapor Deposition (CVD)

PVD coating vs CVD Coated Tool
Above is an example of a Harvey Tool CVD Ball End Mill.


Unlike PVD coating operations, which use high electrical charges and atomic collisions to deposit coatings onto a tool, the CVD method utilizes the chemical properties of the metals to transfer metallic compounds onto the tool. The following steps are required to carry out the CVD operation:

  1. Much like the PVD method, the first step is creating an ultrahigh vacuum within the reaction chamber of around 1 Pa (0.0000145 psi) to eliminate all moisture and impurities.
  2. The internal temperature of the chamber is increased between 600 – 1000°C (1112 – 2012°F).
  3. The temperatures required in the CVD process are significantly higher than PVD coating because this method requires a chemical reaction to occur between gases flowed into the chamber and the substrate. High temperatures are required to initiate and maintain these reactions.
  4. Once the substrate is heated to its desired temperature, the metals intended to be coated onto the tools, which are already in their vapor state, are chemically bonded with a reactive gas (typically chlorine), and flowed into the chamber.
  5. The metallic materials being bonded to a gas keeps it in a gaseous state while it is being transported through the chamber and around the tools.
  6. Hydrogen gas is then pumped into the chamber and mixes with the chlorine and metals.
  7. When this mixture meets the heated substrate, the thermal energy creates a reaction where hydrogen and chlorine bond and leave the metallic materials behind on the tools.
  8. In the chamber, there is an exit vent where the waste gas (H2Cl) is removed.

PVD Coating & CVD Coating, Summarized

Tool coatings are utilized by machinists every day to accomplish prolonged tool life, a more efficient machining operation, and an overall higher quality final part. Most manufacturers use two different types of application techniques, PVD coating and CVD coating. Stay on “In the Loupe” to learn more about tool coatings by reading the following blog posts: Overview of Harvey Tool Coatings: Maximizing Performance and 3 Ways Tool Coatings Increase Tool Life.

Citation:
[1] Ucun, İ., Aslantas, K., & Bedir, F. (2013). An experimental investigation of the effect of coating material on tool wear in micro milling of Inconel 718 super alloy. Wear, 300(1-2), 8–19. https://doi.org/10.1016/j.wear.2013.01.103

3 Ways Tool Coatings Increase Tool Life

Cutting tools are commonly found with an ultra-thin molecular compound coating applied to its cutting surfaces. These coatings are engineered to combat against forces that wear down your cutting tools and lead to catastrophic tool failure. Not only are coatings created for cutting specific materials, but they also limit heat and friction and enhance the performance of your tool. When selecting a coated tool, the machinist must consider how the material and desired cutting operations may break down the cutting edges of the tool, to determine which coating will best serve their needs. Before those decisions can be made, one must understand how coatings increase a tool’s cutting abilities. The following is an in-depth look into the benefits provided by tool coatings and how they work to improve tool life and performance.

What Is a Coating?

Tool coatings consist of organic and inorganic compounds which are applied and adhered onto the substrate using Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD). Compounds are deposited onto the tools in layers until a desired thickness is achieved.

Coated cutting tools provide three main functions:

  1. Provide a thermal barrier between the tool and workpiece
  2. Improve tool lubricity
  3. Increase tool wear resistance

With the proper utilization of these three features, cutting tools can be pushed much harder, run with faster cycle times, and last longer.

1.      Provide a Thermal Barrier Between the Tool and Workpiece

Heat mitigation is essential in machining, as excessive tool and workpiece heating during cutting operations can be detrimental. As the carbide tool’s temperature rapidly increases, its hardness decreases, resulting in greater wear and burn out. Thermal conductivity is a material property used to measure a material’s ability to retain or transfer heat energy. For example, tungsten carbide has a thermal conductivity of 88 W/m.K at 20°C. This means at room temperature, 20°C (68°F), an uncoated carbide tool can conduct 88 Watts of thermal energy per meter with a temperature gradient measured in Kelvin. The materials used in tool coatings do not conduct heat as well with thermal conductivity rates as low as 4.5 W/m.K. This means that a coating with a thermal conductivity of 4.5 W/m.K, the coating would transfer 19.56 times less heat than tungsten carbide.

An experiment showcasing the thermal abilities of coatings is shown below. Both an AlTiN Nano coated tool and uncoated tool were turning 4340 steel at a speed of 155 m/min (508.5 ft/min) and 200 m/min (656.17 ft/min), at a feed rate on 0.5 mm/rev (0.019 in/rev) and a depth of cut of 3.5 mm (0.138 in) [1]. No coolant was used.

uncoated tool thermal gradient

Figure 1: Thermal gradient of the cutting tip of the uncoated tool [1].

tool coatings thermal gradient

Figure 2: The above images, found in a study titled “Experimental Study and Modeling of Steady State Temperature Distributions in Coated Cemented Carbide Tools in Turning,” written by Amol Thakare and Anders Nordgren, showcase the effects of cutting tool speed and tool deformation on temperature distributions in unworn (left) and worn (right) tool.

Comparing the two tools, it is clear that the coated tool absorbs far less heat than the tool without a coating. With lower thermal conductivity rates, tool coatings create a thermal barrier between the carbide and workpiece. This greatly decreases the internal temperature of the carbide as the heat generated during the cutting operations is redirected into the chips and workpiece. With lower temperatures, faster cutting speeds can be attained. Looking at the thermal gradients above, the uncoated tool running at 155 m/min and the coated tool running at 200 m/min roughly have the same surface temperature. This means the coated tool can run 22.5% faster than its uncoated counterpart.

2. Coatings Increase Tool Lubricity

Another key to limiting heat generation and keeping cutting smooth and chatter-free is to decrease the amount of friction between the cutting tool and workpiece. Frictional force is the resistance to motion, and in the case of cutting tools, the force opposing the lateral and radial movements of the tools as it cuts through the workpiece. This opposing force is determined by the coefficient of friction, often denoted as the Greek letter Mu (μ). The friction coefficient is the ratio between the force required to move one surface across another, divided by the pressure between the two surfaces. Minimizing μ is how coatings decrease the overall frictional forces involved in cutting operations because the force of friction is directly proportional to μ.

An example to show how much a coating can reduce the coefficient friction during cutting operations, over an uncoated carbide tool, is shown in the study performed by the University of Technology of Malaysia. In this experiment, 1040 carbon steel was turned at 60 mm/min (2.36 in/min), a depth of cut of 1 mm (0.04 in), a feed rate of 0.06 mm/rev (0.0024 in/rev), and a repeated length of cut of 100 mm (3.937 in) until the tool cut a total length of 1000 m (3280.84 ft) [2]. The coated tool had a TiCN coating, a coating similar to the more popular AlTiN coating. Below are the results:

Figure 3: The above image, found in “Friction and Wear Characteristics of WC and TiCN-coated Insert in Turning Carbon Steel Workpiece,” displays the friction coefficient of the TiCN coated tool and uncoated tungsten carbide tool.

As seen in figure 3, the TiCN coated tool had a much lower coefficient of friction than the uncoated tool. This lower coefficient decreases the frictional forces experienced during cutting operations, reducing heat generation, giving a better part finish, and extending tool life.

Selecting a coated tool with high lubricity would also be ideal for cutting materials with low melting temperatures, as well as materials that generate a tremendous amount of heat during machining, such as high hardness alloys. In materials with low melting points (such as aluminum or other non-ferrous metals), high friction can cause heat generation and sticking of chips. These chips can then cause chip packing in flute valleys and galling on the cutting edge. This galling is called built up edge (BUE) which creates a thicker edge and can break down the tool. With lower friction coefficients, it is more difficult for chips to stick to the tool and for BUE to occur. When cutting materials that would generate high temperatures (such as stainless steels and aerospace alloys), keeping frictional forces at a minimum, will reduce heat generation, and result in smoother cutting, preserving the tool’s cutting edges.

3.      Tool Coatings Increase Tool Wear Resistance

Adding a coating with a high microhardness rating increases a cutting tool’s ability to resist wear and avoid permanent deformations. In the cutting industry, cutting tool grades for tungsten carbide range from grades C1 to C14, depending on what the cutting operation the tool will be performing. Between grades C1 to C14, tungsten carbide has a Vickers Hardness (HV) ranging from 760 HV to 1740 HV. Tool coatings have higher microhardness ratings than tungsten carbide. Adding a coating can increase a tool’s hardness anywhere from 2213 HV using a TiN coating, to 9993 HV with the CVD diamond coating. While a TiN coating would not be chosen solely for its hardness, it shows that even the coating with the lowest hardness is still harder than bare tungsten carbide. By making the cutting tool significantly harder, the ratio of workpiece hardness to tool hardness increases. Increasing the tool’s hardness will allow it to shear off chips and remove material with greater ease, especially against high abrasive materials, while the tool maintains its structural integrity against the extreme forces experienced during cutting operations.

The benefits of increasing tool hardness with its improved performance are demonstrated in an experiment done by Afyon Kocatepe University. In this experiment, a 2 flute micro end mill with a cutting diameter of 4 mm was slotting into Inconel 718 at 20,000 rpm, with a feed rate of 5 micrometers per flute, a depth of cut of 0.2 mm and a length of cut of 120 mm [3]. This cut was performed using both an uncoated and AlTiN coated (3620 HV hardness) carbide end mill with no coolant. Below are optical comparator images of the two tools showing their wear and deformations.

Figure 4: The image above from “An Experimental Investigation of the Effect of Coating Material on Tool Wear in Micro Milling of Inconel 718 Super Alloy,” showcases an uncoated cutting tool.

Figure 5: The image aboves from “An Experimental Investigation of the Effect of Coating Material on Tool Wear in Micro Milling of Inconel 718 Super Alloy,” showcases the difference a coating can make on a cutting tool. Figure 4 displays an uncoated cutting tool, and figure 5 displays a cutting tool with AlTiN PVD coating.

Looking at the two tools, it is evident that the uncoated tool experienced significant flank and crater wear, which resulted in the flaking of its cutting edges. As this tool performed its cuts, flank wear occurred first. This wear happened directly at the cutting edge as the abrasive Inconel alloy began to breakdown the tool. As the flank wear increased past the cutting edge and into the rake face of the tool, crater wear formed. Crater wear is characterized by its depth into the tool. As chips slid across the rake face and increased this crater, pieces of the carbide tool began to flake off, forming a new, weaker cutting edge. This new edge is blunt and will not be capable for cutting the workpiece properly, and will continue to break apart until catastrophic tool failure occurs.

Flank and crater wear are two types of mechanical tool decay that are a direct result of the abrasiveness of the workpiece material. Increasing the microhardness of the cutting tool can combat against these abrasive modes of tool wear. This is proven in figure 5, as the AlTiN PVD coated end mill held up much better in comparison to the uncoated tool as it experienced minimal flank wear. As the coated tool performed its cuts, the only detectable wear was a microfracture along one of its cutting edges, and peeling of the AlTiN coating. The protection provided by the coating against abrasive wear is evident in this example, and with this protection, tool life is significantly increased.

The Benefit of Tool Coatings During Machining

Combining the three main advantages of a tool coating, thermal resistance, increased lubricity, and higher microhardness, not only does the tool perform better, but it lasts longer. Minimizing thermal and abrasive tool wear can substantially prolong tool life.

Citations

      [1] Thakare, Amol, and Anders Nordgren. “Experimental Study and Modeling of Steady State Temperature Distributions in Coated Cemented Carbide Tools in Turning.” Procedia CIRP, vol. 31, 2015, pp. 234–239., doi:10.1016/j.procir.2015.03.024.

      [2] Talib, R.J., et al. “Friction and Wear Characteristics of Wc and Ticn-Coated Insert in Turning Carbon Steel Workpiece.” Procedia Engineering, vol. 68, 2013, pp. 716–722., doi:10.1016/j.proeng.2013.12.244.

[3] Ucun, İ., Aslantas, K., & Bedir, F. (2013). An experimental investigation of the effect of coating material on tool wear in micro milling of Inconel 718 super alloy. Wear300(1-2), 8–19. https://doi.org/10.1016/j.wear.2013.01.103

Overview of Harvey Tool Coatings: Maximizing Tool Performance

Proper tool coating plays a large role during the selection of a CNC cutting tool. At Harvey Tool, coatings are optimized for specific materials and alloys to ensure the highest tooling performance, possible. Each coating offers a unique benefit for the cutting tool: increased strength, enhanced lubricity, heat resistance, and wear mitigation, just to name a few.  

In Benefits of Tool Coatings, the method of applying coatings to tools is examined. In this post, we’ll take a closer look at each Harvey Tool coating to examine its key properties, and to help you decide if it might add a boost to your next CNC application.

Harvey Tool offers a wide range of tool coating options for both ferrous and exotic materials, as well as non-ferrous and non-metallic materials. In the Harvey Tool catalog, coatings are often denoted in a -C# at the end of the product part number.

Harvey Tool Coating Gallery

Harvey Tool Coatings for Ferrous and Exotic Materials

TiN

TiN, or Titanium Nitride (-C1), is a mono-layer coating meant for general purpose machining in ferrous materials. TiN improves wear resistance over uncoated tools and aids in decreasing built-up edge during machining. This coating, however, is not recommended for applications that generate extreme heat as its max working temperature is 1,000 °F. TiN is also not as hard as AlTiN and AlTiN Nano, meaning its less durable and may have a shorter tool life.

Harvey Tool 46062 Tin Tool Coating

Harvey Tool 46062-C1

AlTiN

AlTiN, or Aluminum Titanium Nitride (-C3), is a common choice for machinists aiming to boost their tool performance in ferrous materials. This coating has a high working temperature of 1,400 °F, and features increased hardness. AlTiN excels in not only dry machining, due to its increased lubricity, but also in machining titanium alloys, Inconel, stainless alloys, and cast iron. To aid in its high heat threshold, the aluminum in this coating coverts to aluminum oxide at high temperatures which helps insulate the tool and transfer its heat into the formed chips.

altin tool coating 823816-C3

Harvey Tool 823816-C3

AlTiN Nano

AlTiN Nano or Aluminum Titanium Nitride Nano (-C6) is Harvey Tool’s premium coating for ferrous applications. This coating improves upon AlTiN by adding silicon to further increase the max working temperature to 2,100 °F while also increasing its hardness for increased tool life during demanding applications. Due to its penchant for demanding applications, AlTiN is recommended for hardened steels, hardened stainless, tool steels, titanium alloys, and aerospace materials. These applications often create high levels of heat that AlTiN Nano was designed to combat.

altin nano tool coating

Harvey Tool 843508-C6

harvey tool coating zoomed in

Tool Coatings for Non-Ferrous and Non-Metallic Materials

TiB2

TiB2, or Titanium Diboride (-C8), is Harvey Tool’s “bread and butter” coating for non-abrasive aluminum alloys and magnesium alloys, as it has an extremely low affinity to aluminum as compared to other coatings. Aluminum creates lower working temperatures than ferrous materials, so this coating has a max working temperature of of a suitable 900 °F. TiB2 prevents built-up edge and chip packing, further extending its impressive tool life. TiB2 is not recommended for abrasive materials as the carbide is slightly weakened during the coating process. These materials can cause micro fractures that may damage the tool at high RPMs.

TiB2 can be found on a wide variety of Harvey Tool 2 and 3 flute tools as the premium option for high performance in aluminum alloys.

tib2 tool coating

Harvey Tool 820654-C8

ZrN

ZrN, or Zirconium Nitride (-C7), is a general-purpose coating for a wide variety of non-ferrous materials, including abrasive aluminum alloys. This tool coating is a lower cost alternative to diamond coatings, while still boasting impressive performance through its high hardness levels and overall abrasion resistance. ZrN has a max working temperature of 1,110 °F with strong lubricity in abrasive alloys. This coating is best suited for abrasives, such as brass, bronze, and copper, as well as abrasive aluminum alloys that should not be used with TiB2.

zrn tool coating

Harvey Tool 27912-C7

CVD Diamond Tool Coatings

CVD Diamond, or Crystalline CVD Diamond, is a process where the coating is grown directly onto the carbide end mill. This process dramatically improves hardness over other coatings, improving tool life and abrasion resistance while also allowing for higher feed rates. The trade-off for increased wear resistance is a slight rounding of the cutting edge due to the coating application. Due to its increased wear resistance, CVD is best suited for highly abrasive materials such as graphite, composites, green carbide, and green ceramics. Similarly, these tool coatings have a max working temperature of 1,100 °F, meaning they are not well suited for ferrous applications.

Harvey Tool’s CVD Diamond Coating Options:

diamond tool coatings
Amorphous, CVD 4 μm, CVD 9 μm, PCD Diamond

CVD Diamond (4 μm)

The 4 μm is thinner than the 9 μm allowing for a sharper cutting edge, which in effect leaves a smoother finish.

CVD Diamond 9 μm)

The 9 μm CVD tool coating offers improved wear resistance over the 4 μm CVD and Amorphous coatings due to its increased coating thickness.

Amorphous Diamond

Amorphous Diamond (-C4) is a PVD diamond coating which creates an exceptionally sharp edge as compared to CVD. This coating aids in performance and finish in abrasive non-ferrous applications, as it allows for greatly improved abrasion resistance during machining, while still maintaining a sharp cutting edge necessary for certain abrasives. Due to the thinness of the coating, edge rounding is prevented in relation to CVD diamond tooling. Amorphous Diamond is best suited for use in abrasive plastics, graphite, and carbon fiber, as well as aluminum and aluminum alloys with high silica content, due to their abrasiveness. The max working temp is only 750 °F, so it is not suited for use in ferrous machining applications.2

Harvey Tool 809362-C4

PCD Diamond

PCD Diamond, or Polycrystalline Diamond, is a tool coating that is brazed onto the carbide body. In comparison to the other diamond coatings, PCD does not face the same challenges of other coatings as it pertains to rounded cutting edges, as these edges are ground sharp. PCD has the edge benefits of Amorphous Diamond with the abrasion resistance of CVD Diamond. PCD is the thickest diamond layer offered by Harvey Tool, and excels due to its incredible hardness and abrasion resistance. This tool is best suited for all forms of abrasive, non-ferrous materials including abrasive plastics, graphite, carbon fiber, and composites. Similar to the other non-ferrous tool coatings, PCD is not suited for ferrous applications due to its working temperature of 1,100 °F.

pcd diamond

Harvey Tool 12120

Tool Coating Summary

When deciding on a coating for your application there are many factors to be considered. Different coatings often cross several applications with performance trade-offs between all of them. Harvey Tool offers a “Material Specific Selection” that allows users to choose tooling based upon what materials they are working with. Further, Harvey Tool’s technical team is always a phone call away to help in finding the right tool for your specific applications at 1-800-645-5609. Also, you can contact Harvey Tool via e-mail.

Titan USA Carbide Drills: Jobber, Stub, & Straight Flutes

When navigating Titan USA’s offering of carbide drills, it is imperative to understand the key differences among the three carbide drill styles: Jobber Length, Stub Length, and Straight Flute Drills. The right drill for your application depends on, among other factors, the material you are working in, the job requirements, and the required accuracy.

PRO TIP:

Chip evacuation can be an obstacle for hole making. Pecking cycles can be used to aid in chip removal. Peck cycles are when the drill is brought in and out of the hole location, increasing depth each time until the desired depth is reached. However, pecking cycles should only be used when necessary; this process increases cycle time and subjects the tool to added wear from the repeated engaging and disengaging.

Jobber Length Drills

A carbide Jobber Length Drill is the standard general-purpose drill within Titan USA’s offering. It has a long flute length and an included angle of 118o. These drills are great for general purpose drilling where the tolerances are not as tight as the Stub Drill or Straight Flute Drill. Due to the length of these drills, however, they will be more affected by any lack of rigidity in the set up and can have higher runout, or straying from a desired location, during the drilling operation.

PRO TIP:

To achieve high accuracy and great finish, consider utilizing a Reamer. Reamers are designed to remove a finite amount of material but bring a hole to a very specific size. To do this, first drill 90% – 94% of the desired hole diameter with a Jobber Drill. After 90% – 94% of the material is removed, go in for a finishing pass with a Reamer. Reaming tools are highly accurate and leave a beautiful finish.

Stub Length Drills

Titan USA carbide Stub Length Drills have a shorter flute length, wider included point angle, and a significant drop in helix angle, when compared to Jobber Length Drills. The shorter length and wider tip create for a more rigid tool and, in turn, more accurate holes. The stub drill is the best option when drilling with tight tolerances on shallower holes.

Straight Flute Drills

Carbide Straight Flute Drills have the smallest core of the three drill types mentioned within this post. Titan USA offers Straight Flute Drills with 2 flutes and a 140o included angle. These drills are designed for hole making in materials that create short chips. Materials in which the Straight Flute Drill typically performs best include cast aluminums and cast irons, as well as copper. In addition, this type of drill can work very well in high hardness materials, but the core diameter should first be adjusted to accommodate the increased hardness. For these difficult to machine materials, casting the part with a core hole and then opening it up with the Straight Flute is a great option. This removes some of the stress caused by chip removal and allows for the drill to do what it does best.

Chip removal can be more difficult in this style of carbide drill because the chips are not guided along a helix. With helix flutes, the motion of chip removal is mostly continuous from their initiation point, through the flute valleys, and finally out of the flute valleys. The helix creates a wedge which helps push the chips along, but the straight flute does not have that. It interrupts that natural turning motion created by the drill face which can affect chip evacuation. Due to the interruption in motion this type of drill is better suited for applications involving chips of smaller size.

PRO TIP:

Helix drills create multiple different forces on the part, which can create micro imperfections. The Straight Flute Drills do not create those forces, so the finish is much more consistent down to the micro level. The margins of the Straight Flute Drill also burnish the inside of the hole as they spin, which improves the finish as well. When comparing the Straight Flute Drill to a helix drill, the length of the overall contact point is much shorter in the Straight Flute Drill, and has less heat generation. The decreased heat will also reduce the probability of work hardening.

Selecting Your Perfect Titan USA Carbide Drill

Selecting the correct carbide drill for your application is a crucial step in hole making. The Jobber Drill is a great general-purpose drill and should be utilized in applications requiring long reach. The Stub Drill increases the rigidity with its shorter length of flute, allowing it to drill with higher accuracy. Applications which involve tight tolerances and more shallow holes can be done with the Stub Drill for high-quality results. Lastly, for difficult to machine and hard materials, the Straight Flute Drill is the perfect solution. When the core diameter and chip evacuation is properly addressed, the Straight Flute Drill produces beautifully consistent surface finish and extremely tight tolerances. Similarly, Titan USA offers its carbide drills in both an uncoated option, and AlTiN coating. Traditionally, uncoated tools are general purpose workhorses in a wide variety of materials both ferrous and non-ferrous. AlTiN or Aluminum Titanium Nitride is an enhanced coating specifically made for ferrous materials that extends tool life and performance across a wide range of steels and their alloys.

For more information on Titan USA Drills, and to view its full selection, click here.

We Partnered with Makino & Mastercam to Set MRR Standards with Helical Solutions’ HEV-C-6

Material removal rates (MRR) is the term for the measurement regarding how much material is removed from a part during machining over a set period of time. Material Removal Rate is the key identifier in machine tooling efficiency, as well as the efficiency of both CNC machines and softwares. Radial depth of cut (RDOC) and axial depth of cut (ADOC) are critical elements to MRR, as this determines how and where your tooling is engaging with the workpiece. Applying High Efficiency Milling (HEM) strategies to your milling practice is the best place to start to increase MRR while also keeping tool wear and overall tool life in check.

Utilizing HEM with Helical Solutions’ HEV-C-6 chipbreaker with Mastercam software, Makino machinists were able to use a Makino PS105 VMC to achieve a new industry standard in MRR for 4140 steel alloy.

Setting a New Material Removal Rate Benchmark with Helical

Engineered for High Efficiency Milling (HEM), Helical’s HEV-C-6 was designed for optimal chip evacuation and reduced tool harmonics at high RPMs. Makino machinists utilized these features alongside Mastercam’s highly effective tool paths to create an astonishing material removal rate.  

Watch the video below from Makino to see these impressive feats.

Inside the machine, the HEV-C-6 was spun at 10,695 RPM with Mastercam’s impressively efficient toolpaths to achieve and incredible 40in3 MRR. 

Harvey Performance Company National Application Engineer Don Grandt, who worked with Makino and Mastercam on this project, spoke of what went into this effort.

How did this project initially gain traction?

A Helical Solutions e-mail seen by Makino that highlighted our new HEV-C-6 end mill. They wanted to work with us and Mastercam to do a demo to show off the power of their PS105 Vertical Machining Center with a 1/2″ end mill. Using our tool, they were able to max out the horsepower on the machine to get unbelievable MRR rates.

What considerations were met as you attempted to set this new industry standard?

All tools can only be pushed to the limits of the machine and material. So the goal was to watch the machine’s spindle load to give 100% or greater efficiency of the machine. We also wanted to use a combination of radial step over, axial stepdown, and Feed per Minute to maximize the MRR as well.

Why was Helical’s HEV-C-6 chosen for this project?

The tool was chosen for a couple of reasons. First, the email that Helical sent was boasting some impressive things about this tool, which intrigued Makino. The other reason was Mastercam was working with us in the past and kind of had an idea that with they tool path (Dynamic) and Makino’s machine power and performance, that this could be an incredible collaboration.

What is next for the performance between these three brands?

We have pushed the limits of the Makino PS105 Machine with a half inch endmill so the sky’s the limit with other machines in Makino’s arsenal with greater horsepower and performance. And as far as Mastercam is concerned, they evolve their software yearly with new tool paths and strategies that make it easier and easier on the tool.

For more information on this impressive feat, a webinar hosted by Makino, and featuring Don Grandt, can be found here. Cutting Tool Engineering (CTE) also featured this collaboration in their August 2021 issue as well as in an accompanying blog post written by Jesse Trinque of Mastercam.

Understanding Key Qualities in Micro 100’s Offering of Micro-Quik™ Quick Change Tool Holders

Did you know that, along with supplying the machining industry with premier turning tools, Micro 100 also fully stocks tool holders for its proprietary Micro-Quik™ Quick Change Tool Holder System? In fact, Micro 100’s Spring 2021 Product Catalog introduced new “headless” style tool holders, which are revolutionizing the machine setup process for turning operations.

This “In the Loupe” guide is designed to provide you with insight for navigating Micro 100’s offering, and to help you select the optimal holder style for your operation.

Understanding Micro 100’s Micro-Quik™

Micro 100’s Micro-Quik™ is unlike any other tool change system you may have seen from other tool manufacturers because of its incredible axial and radial repeatability and its ease of use. This foolproof system delivers impressive repeatability, tip-to-tip consistency, and part-to-part accuracy, all the while resulting in tool changes that are 90 % faster than conventional methods.

In all, a tool change that would regularly take more than 5 minutes is accomplished in fewer than 30 seconds.

Try Micro 100’s “Headless” Tool Holders for Incredible Flexibility

Micro 100 Quick Change Tool Holder Selection

Straight Style, Headless Tool Holders

When using a straight style tool holder, you will enjoy significantly enhanced versatility during the machine set up process. These holders are engineered specifically for use in any Swiss, standard lathe, or multi-function lathe, and allow for adjustable holder depth in a tooling block. Radial coolant access ports provide easier access to coolant and the ability to utilize coolant through functionality in tooling blocks that share a static and live tool function, and cannot be plumbed through the back of the holder. Further, their headless design allows for installation through the backside of the tooling block in machines where the work envelope is limited, allowing for a simplified installation process.

Created by Harvey Performance Company Application Engineers, the following videos outline the simple process for inserting each style of Micro 100 Straight Tool Holder into a tooling block.

Micro 100 Straight Holder, Plumbed Style (QTS / QTSL)

In the video, you’ll notice that the first step is to place your Micro-Quik™ tool in this quick change holder, and align it with the locating pin. Then, tighten the locating and locking screw into the whistle notch. This forces the tool against the locking pin, and allows for repeatable accuracy, every time. From there, the quick change tool holder can be installed as a unit into a tooling block. When desired tool position is achieved, set screws can be tightened to lock the holder in place.

Micro 100 Straight Holder, Plumbed & Ported Style (QTSP / QTSPL)

This unique Micro 100 quick change tool holder style is plumbed and ported, allowing for enhanced versatility and coolant delivery efficiency. The setup process using this style of holder is also simple. First, place your Micro 100 quick change tool into the holder, and align it with the locating pin. From there, tighten the locating and locking screw into the whistle notch, forcing the tool against the locating pin and allowing for repeatable accuracy, every time. When plumbed coolant is being used, remove the plumbed plug in the back of the holder, and connect the appropriate coolant adapter and line. Then, the holder can be installed as a unit into the tooling block and locked into place with set screws.

When using ported coolant, make sure that the coolant plug in the back of the holder is tightly installed. Then, be sure to only use one of the radial ports. Simply plug the two that aren’t in use. Install the provided porting adapter to allow for coolant access. Porting options allow for coolant capabilities in machine areas where coolant is not easily accessible.

Headed Tool Holders

headed quick change tool holder

Micro 100’s original quick change tool holder for its Micro-Quik™ system, this style of tool holder for lathe applications features a unique “3 point” locking and locating system to ensure repeatability. When conducting a tool change with this tool holder style, you must follow a simple, 3-step process:

  1. Loosen the tool holder’s set screw
  2. Remove the used tool from the holder
  3. Insert the new tool and retighten the set screw

These headed holders are plumbed through the back of the holder for NPT coolant connection and are available in standard length and long length styles.

Double-Ended Modular Tool Holder System

double ended quick change tool holder

For twin spindle and Y-axis tooling block locations, Micro 100 fully stocks a double-ended modular system. Similar to its single-ended counterparts, this modular is headless, meaning it enhances machine access during the tool block installation process, and the holder depth can be adjusted while in the block. Because this system is double-ended, however, there is obviously no plumbed coolant option through the end of the tool. Instead, coolant is delivered via an external coolant port, the adapter for which is included in the purchase of the modular system. Right hand and left hand tool holders are designed so the set screws are facing the operator for easy access. Both right and left hand styles are designed for right hand turning.

Enjoy Quick Change Tool Holding Confidence & Ease of Use

When opting for a quick change system, machinists long for simplicity, versatility, and consistency. Though many manufacturers have a system of their own, Micro 100’s Micro-Quik™ sets itself apart with axial and radial repeatability, and tip-to-tip consistency. Further, Micro 100 fully stocks several quick change tool holder options, allowing a machinist to select the style that best fits their application.

Micro100 also manufactures and stocks a wide variety of boring tools for the Micro-Quik™. Click here to learn more.

For more information on selecting the appropriate quick change tool holder for your job, view our selection chart or call an experienced Micro 100 technical engineer at 800-421-8065.

quick change tool holder selection chart for Micro100

8 Unique Facts About Thread Forming Taps

Unlike most CNC cutting tools, Thread Forming Taps, otherwise known as Form Taps, Forming Taps, or Roll Taps, work by molding the workpiece rather than cutting it. Because of this, Form Taps do not contain any flutes, as there is no cutting action taking place, nor are there any chips to evacuate. Below are 8 unique facts of Thread Forming Taps (and some may surprise you).

1. Chips Aren’t Formed

When using a Form Tap, chips are not formed, nor is any part material evacuated (Yes, you read that right). With thread forming, the tool is void of any flutes, as chip evacuation is not a concern. Form Taps quite literally mold the workpiece, rather than cut it, to produce threads. Material is displaced within a hole to make way for the threads being formed.

2. Cutting Oils Allow for Reduced Friction & Heat Generation

Did you know that Thread Forming Taps require good lubrication? But why is that the case if chips are not being evacuated, and how does lubrication enter the part with such a limited area between the tool and the perimeter of the hole being threaded? Despite the fact that chips aren’t being formed or evacuated, cutting oils aid the Form Tap as it interacts with the part material, and reduces friction and heat generation. Lube vent grooves are narrow channels engineered into the side of Forming Taps that are designed to provide just enough room for lubricant to make its way into – and out of – a part.

titan thread forming tool

Not all materials are well suited for Thread Forming Taps. In fact, attempting to use a tap in the wrong material can result in significant part and tool damage. The best materials for this unique type of operation include aluminum, brass, copper, 300 stainless steel, and leaded steel. In other words, any material that leaves a stringy chip is a good candidate for cold forming threads. Materials that leave a powdery chip, such as cast iron, are likely too brittle, resulting in ineffective, porous threads.

4. Threads Produced Are Stronger Than Conventional Tapping Threads

Thread forming produces much stronger threads than conventional tapping methods, due to the displacements of the grain of the metal in the workpiece. Further, cutting taps produce chips, which may interfere with the tapping process.

5. Chip Evacuation is Never a Concern With Thread Forming

In conventional tapping applications, as with most machining applications, chip evacuation is a concern. This is especially true in blind holes, or holes with a bottom, as chips created at the very bottom of the hole oftentimes have a long distance to travel before being efficiently evacuated. With form taps, however, chip removal is never a concern.

6. Form Taps Offer Extended Tool Life

Thread Forming Taps are incredibly efficient, as their tool life is substantial (Up to 20x longer than cutting taps), as they have no cutting edges to dull. Further, Thread Forms can be run at faster speeds (Up to 2x faster than Cutting Taps).

Pro Tip: To prolong tool life even further, opt for a coated tool. Titan USA Form Taps, for example, are fully stocked in both uncoated and TiN coated styles.

titan thread forming tools

7. A Simple Formula Will Help You Find the Right Drill Size

When selecting a Tap, you must be familiar with the following formula, which will help a machinist determine the proper drill size needed for creating the starter hole, before a Thread Forming Tap is used to finish the application:

Drill Size = Major Diameter – [(0.0068 x desired % of thread) / Threads Per Inch]
Drill Size (mm) = Major Diameter – [(0.0068 x desired % of thread x pitch (mm)]

8. Thread Forming Taps Need a Larger Hole Size

  1. Thread Form Taps require a larger pre-tap hole size than a cutting tap. This is because these tools impact the sides of the hole consistently during the thread forming process. If the pre-tap hole size is too small, the tool would have to work too hard to perform its job, resulting in excessive tool wear, torque, and possible breakage.

As an example, a ¼-20 cut tap requires a #7 drill size for the starter hole, whereas a ¼-20 roll tap requires a #1 drill size for 65% thread.

The 3 Critical Factors of Turning Speeds and Feeds

Many factors come into play when determining a proper turning speeds and feeds and depth of cut strategy for turning operations. While three of these factors – the ones we deemed to be among the most critical – are listed below, please note that there are many other considerations that are not listed, but that are also important. For instance, safety should always be the main focus of any machining operation, as improper cutting tool parameters can test a machine’s limits, resulting in an accident that can potentially cause significant bodily harm.

Machine condition, type, capabilities, and set-up are all significantly important to an overall successful turning operation, as is turning tool and holder selection.

Turning Speeds and Feeds Factor 1: Machine Condition

The condition of your machine should always be considered prior to beginning a machining operation on a lathe. Older machines that have been used for production operations where hard or abrasive materials are machined tend to have a large amount of backlash, or wear, on the machine’s mechanical parts. This can cause it to produce less than optimal result and may require that a tooling manufacturer’s recommended speeds and feeds parameters need to be dialed back a bit, as to not run the machine more aggressively than it can handle.

turning speeds and feeds

Factor 2: Machine Type and Capabilities

Before dialing in turning speeds and feeds, one must understand their machine type and its capabilities. Machines are programmed differently, depending on the type of turning center being used: CNC Lathe or Manual Lathe.

CNC Lathe Turning Centers

With this type of machine, the part and tool have the ability to be set in motion.

CNC lathe turning centers can be programmed as a G96 (constant surface footage) or G97 (constant RPM). With this type of machine, the maximum allowable RPM can be programmed using a G50 with an S command. For example, inputting a G50 S3000 into your CNC program would limit the maximum RPM to 3,000. Further, with CNC Lathe Turning Centers, the feed rate is programmable and can be changed at different positions or locations within a part program.

Manual Lathe Turning Centers

With this type of machine, only the part is in motion, while the tool remains immobile.

For manual lathe turning centers, parameters are programmed a bit differently. Here, the spindle speed is set at a constant RPM, and normally remains unchanged throughout the machining operation. Obviously, this puts more onus on a machinist to get speed correct, as an operation can quickly be derailed if RPM parameters are not optimal for a job. Like with CNC lathe turning centers, though, understanding your machine’s horsepower and maximum feed rate is critical.

Factor 3: Machine Set-Up

turning speeds and feeds proper tool setup
Excessive Tool Stickout. Digital Image, Hass Automation. https://www.haascnc.com/service/troubleshooting-and-how-to/troubleshooting/lathe-chatter—troubleshooting.html

Machining Conditions

When factoring in your machine set-up, machining conditions must be considered. Below are some ideal conditions to strive for, as well as some suboptimal machining conditions to avoid for dialing in proper turning speeds and feeds.

Ideal Machining Conditions for Turning Applications

  • The workpiece clamping or fixture is in optimal condition, and the workpiece overhang is minimized to improve rigidity.
  • Coolant delivery systems are in place to aid in the evacuation of chips from a part and help control heat generation.

Suboptimal Machining Conditions for Turning Applications

  • Utilizing turning tools that are extended for reach purposes, when not necessary, causing an increased amount of tool deflection and sacrificing the rigidity of the machining operations.
  • The workpiece clamping or fixturing is aged, ineffective, and in poor condition.
  • Coolant delivery systems are missing, or are ineffective
  • Machine does not feature any guarding or enclosures, resulting in safety concerns.

Cutting Tool & Tool Holder Selection

As is always the case, cutting tool and tool holder selection are pivotal. Not all turning tool manufacturers are the same, either. The best machinists develop longstanding relationships with tooling manufacturers, and are able to depend on their input and recommendations. Micro 100, for example, has manufactured the industry’s highest quality turning tools for more than 50 years. Further, its tool holder offering includes multiple unique styles, allowing machinists to determine the product that’s best for them.

lathe tool holder
Pro Tip: Be sure to take into consideration the machine’s horsepower and maximum feed rate when determining running parameters.

Bonus: Common Turning Speeds and Feeds Application Terminology

Vc= Cutting Speed

n= Spindle Speed

Ap=Depth of Cut

Q= Metal Removal Rate

G94 Feedrate IPM (Inches Per Minute)

G95 Feedrate IPR (Inches Per Revolution)

G96 CSS (Constant Surface Speed)

G97 Constant RPM (Revolutions Per Minute)

CNC Machining & 3D Printing: A Hybrid Approach to Precision Manufacturing

With recent advancements in 3D printing capabilities, it is becoming easier for manufacturers to use additive manufacturing to create parts from a wide variety of materials, including polymers like ABS, TPE, and PLA as well as carbon fiber composites, nylon, and polycarbonates. Even pricey metals like Titanium, Stainless Steel, and Inconel are becoming increasingly common in the world of additive manufacturing as well.

There is no doubt that the additive manufacturing space will continue to develop and grow in the coming years, but will it render subtractive manufacturing methods like CNC Machining obsolete? Absolutely not. In fact, precision CNC machining is likely more important to the additive manufacturing process than you may think, as a new process called “hybrid manufacturing” is quickly taking hold in the industry.

3d printing metal
3D printing of metal parts is becoming more common, but subtractive manufacturing is an important part of manufacturing precision additive parts.

Additive Manufacturing vs. Subtractive Manufacturing

Before implementing a hybrid manufacturing approach, it is important to understand the pros and cons of each method. Here is a quick breakdown of both additive and subtractive manufacturing, and the benefits and drawbacks of each.

Additive ManufacturingSubtractive Manufacturing
Adds material layers to create partsRemoves material layers to create parts
Slower process, better for small production runsFaster process, better for large production runs
Better for smaller partsBetter for larger parts
Rough surface finish that requires significant post-operation finishingMore definied surface finish with minimal post-operation finishing required
Less precise part tolerancesAble to hold extremely precise part tolerances
Cheaper material costsMore expensive material costs
Less material wasteMore material waste
Intricate details easier to createIntricate details can require complex programs and additional capabilities (5 axis)

Using CNC Machining to Create Precise 3D Printed Parts

Looking at the chart above, you will notice that one of the key differences between additive manufacturing and subtractive manufacturing is the surface finish and tolerances that can be achieved with each method. This is where a hybrid approach to additive manufacturing can be extremely beneficial.

As parts come off the printer, they can be quickly moved into a CNC machine with a program designed for part completion. The CNC machine will be able to get 3D printed parts down to the tight tolerances required by many industries and reach the desired surface finish. Advanced finishing tools and long reach, tapered tools from brands like Harvey Tool can easily machine the tight geometries of 3D printed parts, while extremely sharp diamond-coated tooling and material-specific tools designed for plastics and composites can work to create a beautiful, in-tolerance finished part regardless of the material.

long reach end mill
Long reach tools can easily machine hard to reach, intricate part details on 3D printed parts.

By designing a workflow like this in your shop, you can spend less time worrying about the precision of printed parts by adding in subtractive operations to keep material costs low, create less waste, and keep parts in tight tolerances for precision machining excellence.

Using 3D Printing to Increase CNC Machining Efficiency

If your shop is focused completely on subtractive manufacturing methods, you are probably thinking that there is no need for an additive option in your shop. Can’t a CNC machine create everything a 3D printer can, and in less time? Not necessarily. Again, by using the two methods together and taking a hybrid approach, you may be able to lower your manufacturing and material costs.

For example, you could machine the bulk of a part with typical subtractive machines, which would likely take a very long time using additive methods. Then you can go back to that part with a 3D printer to add intricate features to the part that may take complex programming and hours of planning on a subtractive machine. An impeller is a great example, where the bulk of that part can be machined, but the tricky fins and blades could be printed onto the part, and then finished back on the CNC machine.

3d printed metal parts
3D printed impeller waiting for finishing operations

The ability of additive machines to literally “add-on” to a part can also make for a cheaper approach to part design. Instead of using expensive materials like Inconel or Titanium to machine an entire part, portions of the part that do not require extreme heat resistance could be machined out of cheaper steel, while the heat resistant portions using expensive materials can be added later through additive methods.

Hybrid Manufacturing Machines

As hybrid manufacturing workflows become more popular, so do new hybrid manufacturing machines. These hybrid machines are all-in-one machines where both additive and subtractive manufacturing can be performed in a single setup. Many of these machines offer metal 3D printing as well as multi-axis machining capabilities, ready for even the most complex parts thrown their way. With a bit of customization, large-scale 3D printing machines or CNC mills can be retrofit to allow for hybrid manufacturing with add-ons from companies like Hybrid Manufacuring Technologies.

hybrid manufacturing machines
Example of a hybrid machine add-on from Hybrid Manufacturing Technologies, featuring 3D printing spindles and milling tools in the same machine carousel.

As manufacturing and design techniques get progressively “smarter” with CAM/CAD programs offering generative design and artificial intelligence, these hybrid machines could become a new standard in high-end machine shops working in advanced manufacturing industries like aerospace, medical, defense, and the mold, tool & die market.

Overall, in 2021 we are still early on in this new revolution of hybrid machining and advanced design methods, but it is important to understand the role that adding a CNC machine could have in your additive-focused shop, and vice versa. By combining additive and subtractive together, shops can mitigate the cons of each method and take full advantage of the benefits of having both options available on the shop floor.

The Secret Mechanics of High Feed End Mills

A High Feed End Mill is a type of High-Efficiency Milling (HEM) tool with a specialized end profile that allows the tool to utilize chip thinning to have dramatically increased feed rates. These tools are meant to operate with an extremely low axial depth so that the cutting action takes place along the curved edge of the bottom profile. This allows for a few different phenomena to occur:

  • The low lead angle causes most of the cutting force to be transferred axially back into the spindle. This amounts to less deflection, as there is much less radial force pushing the cutter off its center axis.
  • The extended curved profile of the bottom edge causes a chip thinning effect that allows for aggressive feed rates.

The Low Lead Angle of a High Feed End Mill

As seen in Figure 1 below, when a High Feed End Mill is properly engaged in a workpiece, the low lead angle, combined with a low axial depth of cut, transfers the majority of the cutting force upward along the center axis of the tool. A low amount of radial force allows for longer reaches to be employed without the adverse effects of chatter, which will lead to tool failure. This is beneficial for applications that require a low amount of radial force, such as machining thin walls or contouring deep pockets.

high feed mill roughing
Figure 1: Isometric view of a feed mill engaged in a straight roughing pass (left), A snapshot front-facing view of this cut (right)

Feed Mills Have Aggressive Feed Rates

Figure 1 also depicts an instantaneous snapshot of the chip being formed when engaged in a proper roughing tool path. Notice how the chip (marked by diagonal lines) thins as it approaches the center axis of the tool. This is due to the curved geometry of the bottom edge. Because of this chip thinning phenomenon, the feed of the tool must be increased so that the tool is actively engaged in cutting and does not rub against the workpiece. Rubbing will increase friction, which in turn raises the level of heat around the cutting zone and causes premature tool wear. Because this tool requires an increased chip load to maintain a viable cutting edge, the tool has been given the name “High Feed Mill.”

high feed end mill ad

Other Phenomena Due to Curved Geometry of Bottom Edge

The curved geometry of the bottom edge also sanctions for the following actions to occur:

  • A programmable radius being added to a CAM tool path
  • Scallops forming during facing operations
  • Different-shaped chips created during slotting applications, compared to HEM roughing

Programmable Radius

Helical Solutions’ High Feed End Mills has a double radius bottom edge design. Because of this, the exact profile cannot be easily programmed by some CAM software. Therefore, a theoretical radius is used to allow for easy integration.  Simply program a bullnose tool path and use the theoretical radius (seen below in Figure 2) from the dimensions table as the corner radius.

high feed mill programmable radius
Figure 2: Programmable radius of a double radius profile tool

Managing Scallops

A scallop is a cusp of material left behind by cutting tools with curved profiles. Three major factors that determine the height and width of scallops are:

  1. Axial Depth of Cut
  2. Radial Depth of Cut
  3. Curvature of Bottom Edge or Lead Angle

Figure 3 below is a depiction of the scallop profile of a typical roughing cut with a 65% radial step over and 4% axial depth of cut. The shaded region represents the scallop that is left behind after 2 roughing passes and runs parallel to the tool path.

roughing cut scallop profile
Figure 3: Back view of roughing cut with a 65% radial step over

Figures 4 and 5 show the effects of radial and axial depth of cuts on the height and width of scallops. These figures should be viewed in the context of Figure 3. Percentage by diameter is used rather than standard units of measurement to show that this effect can be predicted at any tool size. Figure 4 shows that a scallop begins to form when the tool is programmed to have a radial step over between 35% and 40%. The height increases exponentially until it is maximized at the axial depth of cut. Figure 5 shows that there is a linear relationship between the radial step over and scallop width. No relationship is seen between scallop width and axial depth of cut as long as ADOC and the radius of curvature of the bottom cutting edge remains consistent.

graph of scallop height versus depth of cut
Figure 4: Graph of Scallop Height vs. Depth of Cut
graph of scallop width versus depth of cut
Figure 5: Scallop Width vs. Depth of Cut

From the graphs in Figures 4 and 5 we get the following equations for scallop dimensions.

Notes regarding these equations:

  • These equations are only applicable for Helical Solutions High Feed End Mills
  • These equations are approximations
  • Scallop height equation is inaccurate after the axial depth of cut is reached
  • RDOC is in terms of diameter percentage (.55 x Diameter, .65 x Diameter, etc…)

Shop Helical Solutions’ Fully Stock Selection of High Feed End Mills

Curvature of the Bottom Edge of High Feed End Mills

The smaller the radius of curvature, the larger the height of the scallop. For example, the large partial radius of the Helical Solutions High Feed End Mill bottom cutting edge will leave a smaller scallop when compared to a ball end mill programmed with the same tool path. Figure 6 shows a side by side comparison of a ball end mill and high feed mill with the same radial and axial depth of cut. The scallop width and height are noticeably greater for the ball end mill because it has a smaller radius of curvature.

feed mill versus ball end mill
Figure 6: Scallop diagram of High Feed Mill and Ball End Mill with the same workpiece engagement

Full Slotting

When slotting, the feed rate should be greatly reduced relative to roughing as a greater portion of the bottom cutting edge is engaged. As shown in Figure 7, the axial step down does not equate to the axial engagement. Once engaged in a full slot, the chip becomes a complex shape. When viewing the chip from the side, you can see that the tool is not cutting the entirety of the axial engagement at one point in time. The chip follows the contour on the slot cut in the form of the bottom edge of the tool. Because of this phenomenon, the chip dips down to the lowest point of the slot and then back up to the highest point of axial engagement along the side. This creates a long thin chip that can clog up the small flute valleys of the tool, leading to premature tool failure. This can be solved by decreasing the feed rate and increasing the amount of coolant used in the operation.

high feed mill chip formation
Figure 7: Formation of a chip when a feed mill is engaged in a full slotting operation.

In summary, the curved profile of the bottom edge of the tool allows for higher feed rates when high feed milling, because of the chipping thinning effect it creates with its low lead angle. This low lead angle also distributes cutting forces axially rather than radially, reducing the amount of chatter that a normal end mill might experience under the same conditions. Machinists must be careful though as the curved bottom edge also allows for the formation of scallops, requires a programmable radius when using some CAM packages, and make slotting not nearly as productive as roughing operations.