A Practical Approach to Milling Titanium - flute end mill cutter
A rubber-reinforced carrying case protects the drill bits from accidental drops and makes organization and transportation a snap. These drill bits work well on stainless steel and last a long time.
For affordable drilling options, we chose these bits made of a proven material with a simple and functional design. The Comoware cobalt twist bit set includes 15 bits made of M35 cobalt alloy steel that dependably penetrate stainless steel. The bits feature an easy-to-sharpen split point and a straight shaft. They range in size from 0.0625 inch to 0.375 inch, including two each of the popular 0.0625-inch, 0.09375-inch, and 0.125-inch sizes, for a total of 12 different bit sizes. The kit comes in a lightweight plastic carry case with easy-to-read printed bit-size indexing.
In our tests, we appreciated the Milwaukee step bits’ ability to drill precise holes without a center punch using a handheld drill. They tapped into the stainless steel quickly and worked smoothly. We also noted how easily they worked to enlarge existing holes—a task that’s nearly impossible to do well with regular twist drill bits. Sharpening the bits was surprisingly easy but required a completely different technique than twist bits. We used a diamond sharpening stone to flatten the smaller flute edge, and it only took about 5 minutes.
Because of its hardness, stainless steel is an unforgiving construction medium. Usually, there is only one chance to achieve the perfect drill hole. Another crucial consideration when purchasing drill bits for stainless steel is the drill bit number or size.
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Stusak emphasized the benefits of these machining strategies by explaining that the basic principle of metal cutting is forming a chip properly in relationship to edge geometry so that you are shearing the material, not plowing it. Both roughing and finishing benefit from optimized machining strategies, but especially roughing, where machining time can be greatly reduced.
We spent several days researching drill bits for stainless steel and shopping around for the best options available online. Although solid carbide drill bits may be the professional machinist’s choice for drilling stainless steel, they are incredibly expensive. Other options like titanium-coated HSS are inexpensive but lack durability. We narrowed our search to cobalt drill bits because they can drill hard metals repeatedly without dulling right away, and they can be resharpened many times to extend their working life.
He pointed out that while getting material roughed out is difficult and can cause multiple problems, optimized roughing with 6-10 percent maximum radial stepovers is effective on heat-resistant superalloys (HRSA) and titanium. “And you can use these same tools to then finish a lot of these parts as well so you are using more traditional side mill finishing,” he said.
It’s important to have the right CAM software to avoid wasted rapid travel movement, which increases cycle time. There are times when it is better to take a more conventional cutting pass. One example is when the width of cut is short with, say, a 0.5" (12.7-mm) end mill with the intention of cutting a length of the part that’s 0.5" long and the process needs to remove 0.3" (7.62 mm) of material. In this example, Horn recommends taking all the material off in one or two passes instead of 30 passes. To be efficient, the tool must stay on the part and limit time-wasting retraction.
There are other advantages. “By minimizing the width of cut you can elevate the surface footage on most alloys, with the exception of nickel-based alloys,” said Stusak. “You can’t elevate cutting speed that much because it is impossible to eliminate the heat in the cut, but for Ti6Al4V we have case studies where we have machined up to 400 sfm at 4 percent radial engagement with these tools.”
Not every part is a good candidate for high-speed machining. The choice of strategy is a function of the part geometry and size. Some of the testing that’s being seen has been calling for machining Inconel, titanium, and stainless with light depths of cut, high speeds and low radial engagement and feed rates.
We also keyed in on bits with 135-degree points as the recommended angle for efficient drilling into hard metal at the required lower speed and higher pressure. Other variables, such as split or pilot point, flat or 3-flat shank, or various coatings held lower priority. Lastly, we factored in top brand names, which often equate to greater consistency and availability.
The ECI-H4S-CFE end mill is a short, four-flute design with different helixes (35o and 37o) and variable pitch for chatter dampening. It can be used for high MRR roughing and finishing, with full slot milling up to 1×D. It is also available with the new AlTiCrSiN IC608 coating for machining at elevated temperatures.
If it’s a very shallow “depth of part,” the machinist will not get the economy of the end mill and high speed and will experience a lot of excess vibration. The reason is if a shop runs a shallow axial depth of cut, it reduces MRR and the operation may not be as efficient as other methods with larger radial and shallower axial stepovers.
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In some project settings, a single step drill bit can replace an entire set of twist bits. Step bits offer the advantage of fast, clean precision drilling into thin stainless steel or sheet metal without the need to change between different bit sizes. Each one of the three cobalt step drill bits in Milwaukee’s set is engineered to drill up to 1,000 holes into 14-gauge steel. They feature a rapid strike tip for fast starts without a center punch, elongated dual flutes to minimize heat, and finer step increments for smoother operation. Hole sizes are laser engraved inside the flutes for easy reference.
Understanding the composition of these materials is key to understanding the limitations with cutting speed. “Workpiece hardness and material composition have a huge bearing on machinability,” he explained. “Nickel-based, cobalt-based, and ferrous-based superalloys have certain alloying elements in them that won’t allow elevating the sfm because you can’t eliminate the heat in the cut no matter what you do with the width of cut or cutting speed. [Cutting speeds have] to stay between 80 to 110 sfm depending on the hardness of the material.”
Not all drill bits achieve results in the same way. To identify the best drill bits for stainless steel, learning about characteristics like material, coating, frequency of use, and drill bit number are critical. Read on to learn the factors to consider as you search for the best drill bits for your projects that involve stainless steel.
In addition to ultrahard materials and protective coatings, drill bit users who seek longevity should ensure the bit can be sharpened. While drill bits infused with carbide or cobalt keep their edge longer than a standard bit, investing in a set for life often means resharpening the dull drill bits over time.
“Finishing is typically done with a 45o helix end mill for hardened materials up to 65 HRC because the higher helix angle shears the material more effectively,” he said. “End mills with a 60o helix angle are used on nonferrous materials like aluminum and even high-nickel-content alloys in finishing applications. In general, a variable pitch end mill with a 35 to 38o helix angle is the most common we see in the industry because it has a good balance of edge strength and core diameter, and it’s a little bit more up sharp in the cut where it slices through the material more effectively vs a 30o helix end mill.”
Though drill bits for stainless steel pull heavier duty, they are also made of more durable materials. Regularly maintained and properly stored, these kinds of drill bits may last a lifetime.
Many manufacturers complement construction materials like drill bits with metal coatings. These coatings promote penetration and protection of the drill bit. Black oxide coatings reduce friction and heat—a significant consideration when drilling metals. Black oxide also protects against corrosion and water, keeping the drill bits functional for a longer period.
These optimized high-speed and high-efficiency machining strategies are the wave of the future. And they are here today. According to Ball, 80-90 percent of CAM software suppliers have some sort of optimized milling strategy for roughing and 80-90 percent of the major cutting tool manufacturers have some sort of multi-flute products for these strategies.
The objective of both high-speed and high-efficiency machining strategies is to improve MRR, according to Yair Bruhis, global product and application manager for YG-1 Tool Co., Vernon Hills, Illinois. High-efficiency machining increases cutting by limiting air cutting time. “Because the two machining strategies are so effective, people want to switch everything towards them,” said Bruhis. “But it all depends on the part and the machining parameters. Sometimes, I can look at the part and state that it can’t be machined with high-efficiency strategies because of the shape and complexity of the part, or the machine’s capabilities, or the part features and programming, among other factors.
The added cobalt content makes these drill bits harder and more resistant to heat buildup than a typical HSS bit, giving them much greater durability. Also, unlike carbide tips or titanium coatings, cobalt drill bits can be resharpened when the tip becomes worn. These bits offer precision to users who drill stainless steel and other hard materials.
YG-1 has developed standard tools specifically for high-speed machining of titanium, but about 30 percent of its tools for this application are still custom made, with special lengths and corner radii. “One of the trends with high-speed machining is the increased number of flutes needed to take light cuts and run very fast,” he said. “The trend of the last five years is for five, six, seven and nine flutes,” he said. The advantage is longer tool life and better heat and chip control as well as machining performance.
The Drill America bits offered a similar drilling experience as our Best Overall pick because of their similar design features, but this set boasts improved durability thanks to a higher cobalt content. Both sets offered the same drill-bit size assortment, round shank, and 135-degree split-point construction. The Drill America bits remained noticeably sharper after an equal number of test holes, but they required three or four more passes on the grinder to sharpen.
The following is a consensus report of an interview held with Tonne, Eric Carbone, application and sales engineer; John Kollenbroich, head of product management; and Jeff Shope, application and sales engineer.
“We determine the process and program and run it within a range of speeds and feeds and estimate a cycle time,” Bruhis said. “Once the customer has a chance to run the program that we have set, we then can get feedback with real machining time results and, if the cycle time is too long and the cost is not in line with expected results, we make the required adjustments.”
The advantage of multi-flute end mills is that operators can take higher feed rates because of the reduction in DOC and stepover with high-temperature, heat-resistant materials. “These metals don’t like to be machined in the conventional way with large DOCs and large radial stepover and slow feed rates,” said Ball. “Multi-flute tools allow increased MRRs without work hardening because you can run faster feed rates and lighter radial stepovers with more teeth.”
The goal is to maximize flute length because that’s what will provide the best MRR in combination with 5 and 10 percent stepovers. Another way to determine tool selection is to decide whether to simply switch to high-feed milling and ramp in with a conventional end mill and rip the stock out.
The ECP-H7-CF multi-flute (seven flutes) end mill has a hard substrate, IC902 ultra-fine carbide grade with 9 percent cobalt, and is TiAlN PVD coated. It is suitable for machining various materials, including hard steel and cast iron, at high cutting speeds, according to Iscar.
He added: “We have started to play a lot more with variable indexes and [helixes] in multi-flute cutting tools because of their potential for more cutting pressure due to increased tool contact with the workpiece. However, it’s necessary to change [helixes], rakes and indexes to vary the geometry in such a way that it breaks up chatter and harmonics and still retains the tool’s ability to cut efficiently.”
The highest MRR possible in high-speed machining with multi-flute tools occurs when the process engages the full flute length of the tool. The more flutes, the larger the core diameter for rigidity. Typically, the first thing to look at when considering high-speed machining is the size of the part and flute length to decide the diameter of the tool, according to Horn. An inch of actual flute length might be handled by a 3/8" (9.5-mm) diameter tool, and two inches of actual flute length by a 5/8" (15.8-mm) diameter tool.
With high-temperature-resistant, nickel-based alloys being used more commonly by its customers, Seco Tools LLC, Troy, Mich., is focused on maximizing metal removal rates using high-speed, high-efficiency optimized roughing strategies, according to Jay Ball, solid-carbide product manager.
According to the company, time and cost savings and increased part quality result. Tool life is increased due to shorter toolpaths. Tolerance deviations due to heat warping at the tool are minimized, and axial deviations of the machine are smoothed, offering a higher quality surface finish in a shorter time frame. Circle Segment end mills feature unique forms with large radii in cutting areas of the mills, allowing a larger axial DOC during prefinishing and finishing operations.
Milwaukee Cobalt Red Helix drill bits make it easy to drill into hard stainless steel. This set includes 15 bits made of M35 cobalt alloy steel. They feature pilot points for fast, precise surface penetration without a center punch or pilot hole and 3-flat shanks to eliminate the hassle of bits spinning in the chuck. Bit sizes range from 0.0625 inch to 0.375 inch.
The 3-flat shanks of these bits eliminate slippage in the drill chuck. The combination of secure chucking, easy starting, and smooth operation make these bits an excellent choice for use in cordless drills at low speed for hard stainless steel or higher speed for mild steel. The kit includes Milwaukee’s #1, #4, and #9 step bits. The #1 drills from 0.125-inch to 0.5-inch holes in steps of 0.03125 inch. The #4 bit makes holes 0.1875 inch to 0.875 inch in 0.0625-inch steps. The #9 bit drills 0.875-inch to 1.125-inch holes in 0.0625-inch steps.
Horn’s solid-carbide tools with seven or nine flutes with large DOCs and 10-15 percent stepover—as a rule of thumb to start with—help with these strategies, but the machine tool must have the required acceleration and deceleration. An older machine with rapids of 600 ipm will not be sufficient. Similarly, the look-ahead that newer machines have is also required.
He also noted that the trend in titanium alloys and exotics machining in the last four or five years is toward high-speed machining for medium to large parts because the cost of removing titanium or Inconel is much higher than that of aluminum or steel.
“When major OEMs call me in, it’s generally to improve tool life, the process, or both,” Bruhis continued. “It could be a new project with them facing a serious issue. It might be a problem with part quality, or cycle time or delivering parts in time or total cost, but it’s almost never because of the cost of the tool since YG-1 offers a very attractive performance-to-cost package.”
Bruhis described how he evaluates and determines an approach to a titanium machining project. “I typically inquire first about the machine capability, whether three-, four-, or five-axis, vertical or horizontal, fixturing and tooling,” he said. He added that in the majority of cases, specific end mills are selected based on axial or radial cut, speeds and feeds, and programming for high-speed and high-efficiency machining.
Folks who want to be ready for tough steel drilling projects that might come up should consider these cobalt bits from Bosch. The kit includes 14 bits ranging in size from 0.0625 inch to 0.5 inch. They are made of M42 cobalt alloy steel, which is one of the best bit materials for drilling hard metals like stainless steel, cast iron, or titanium. The bits feature easy-to-sharpen split points and 3-flat shanks for easy, secure chucking into the drill. They also feature thicker threading than other twist bits, which helps them remove material more efficiently in less time.
Chip-splitting technology reduces the radial tool pressure encountered with long lengths of cut and helps break up the chips, producing more manageable chips for the operator or the chip pan or conveyor to remove, Stusak explained. “The key to machining difficult-to-machine materials is the radial engagement,” he said. “You want to minimize the width of cut or arc of contact to beat the heat.” By minimizing the width of cut, not as much heat transfers into the tool because of the limited amount of cut time on the end mill.
Stainless steel is an extremely hard material. Low-carbon steel bits, like those used to drill into wood, do not perform when applied to stainless steel. Therefore, a drill bit for use with stainless steel must be harder than the steel itself. One way that manufacturers achieve this hardness is by infusing materials that facilitate penetration and protect against overheating.
The ECKI-H4R-CF four-flute end mill features corner radii for aerospace applications and either of two coatings, IC300 TiCN or IC900 AlTiN. It offers variable pitch and variable helix and a special edge prep for machining titanium.
If converting fractions of an inch to the metric system seems like no fun, this 19-piece drill bit set can help. Not only are these Stroton bits metrically sized in increments of 0.5 millimeters, from 1 millimeter to 10 millimeters, they also feature a unique three-stepped pilot-point design that penetrates stainless steel without traveling across the flat surface. The bits are constructed of tough M42 cobalt alloy steel for improved durability.
These machining strategies require more just than the right carbide grade, insert and geometry—the way of approaching the material is also critical. The goal of high-efficiency machining is to reduce the width of cut and increase the length of cut to reduce cutting forces, which allows faster machining. Sometimes it is quicker that way, and sometimes it is quicker using traditional high-feed cutters. Many times with dynamic machining there can be much wasted movement. Applying it depends on the application and complexity of the features, such as pocketing, that are involved.
Horn’s DSFT end mills—part of the DS line of high-DOC, low-radial-engagement tools—are designed for trochoidal machining. To be effective, DS tools require a solid machine spindle with close runout and a capable controller for programming. CAD programs are available to create simulation of machining time estimates to decide whether traditional end milling or high-speed machining is best. In addition, there are a number of software tools available to evaluate the economics of these tooling decisions.
High-speed metal drilling creates excessive friction and heat. The extra stress placed on standard drill bits tends to wear them out quickly. Individuals who intend to drill stainless steel frequently should be sure to buy bits designed with longevity in mind.
We really liked the effectiveness of the pilot-point design. Instead of using a punch to mark the starting point and reduce bit travel, the pilot point allowed us to start drilling directly into the flat surface. However, due to its multitiered structure, we noted that the pilot point complicates the process of sharpening the bit. We worked through it slowly and with extra caution, we achieved satisfactory results.
Titanium carbonitride (TiCN) is likely the most durable metal coating available. TiCN bits are blue-gray. Their coating makes them incredibly resistant to wear and capable of enduring high-speed and high-frequency use.
Here’s how leading tooling manufacturers are helping customers put these tools to work in machining titanium, nickel-based alloys, superalloys, Inconel and stainless steel.
“All four of those strategies are essentially the same,” said Stusak. “We have developed multi-flute tools, and specifically a seven-flute tool with chip splitting technology to allow very light widths of cut depending on the length of the flute on the end mill. These strategies actively manage all four of the attributes in the CAM systems—including the radial width of cut, the arc of contact, chip thickness and the feed rate—for optimized performance,” he said.
This 29-piece professional-grade drill bit set from Irwin Tools covers an abundance of applications. The bit circumference spans 0.0625 inches to 0.5 inches by increments of 0.0156 inches. The bits themselves are heat- and abrasion-resistant, thanks to their industrial-grade high-speed steel cobalt-alloy construction. To aid penetration, these bits feature 135-degree split-tip points. Besides making these bits suitable for ultrahard materials like steel, the quality construction materials ensure longevity.
Removing metal is important, and doing it fast enough to make money is more important. To capitalize on the latest machining strategies for milling difficult-to-machine materials, Iscar Metals Inc., Arlington, Texas, continues to add to its lines of multi-flute, solid-carbide end mills, according to Bryan Stusak, national product manager–milling. Iscar has designed solid-carbide end mills specifically for milling strategies, including high-speed milling, high-efficiency milling, optimized roughing and proprietary CAM strategies like Mastercam’s Dynamic Milling.
Besides the component, programming strategy and software play into this as well. If a shop is performing high-efficiency or high-speed milling, it must have the horsepower and torque required to drive the tool. If it runs the wrong software, there will be a lot of costly, wasted moves.
Like other companies contributing to this article, Horn USA Inc., Franklin, Tenn., stresses both the importance of multi-flute tool design and customer collaboration for tooling success. “I would describe us as an engineering-driven company that approaches tooling solutions for its customers with finesse,” said Edwin Tonne, training and technical specialist. Horn, which is well known for its grooving and cut-off turning tools, offers a broad line of products, including solid-carbide end mills, drills, and indexable milling cutters, as well as its turning products. More than 40 percent of its cutting tools are specials. Horn has developed multi-flute end mills used to machine titanium, Inconel, stainless and other high-temperature-resistant metals using high-speed and high-efficiency machining strategies to achieve the highest MRR.
The ECY-S5 end mill with five flutes features a general-purpose substrate and AlTiCrSiN coating (IC608) for shoulder or full slot high-speed milling or trochoidal or peel milling. Its primary application is stainless but it can also be used to machine nickel-based, high-temperature alloys.
Drill bit numbers are related to wire gauge size. The larger the bit number, the smaller the diameter of the resulting hole. For example, a number 80 drill bit creates a hole with a diameter of 0.0135 inches. As the diameter grows larger, the bit number grows smaller. A number 1 drill bit, in comparison, has a diameter of 0.2280 inches.
This set of M42 cobalt drill bits from Drill America includes 29 pieces from 0.0625 inch to 0.5 inch in 0.015625-inch increments. The bits are finished with gold oxide, which acts as a built-in lubricant to minimize heat, making this one of the best choices for a long working life when drilling tough metals. Each bit is made of high-grade M42 cobalt alloy steel and features a split point and straight shaft.
While the Stroton M42 cobalt bits feature round shanks, which can allow slippage in the chuck, we did not experience any slippage during tests, possibly thanks to the unusual low-profile stepped split-point design. Unlike the more pronounced pilot points on other bits we tested, the low-profile Stroton tips featured a three-step tip that seemed to penetrate faster and smoother than other designs, with or without a center punch starting point.
Following the guidelines on this revolutions per minute chart, we used each bit to drill four holes into 0.125-inch thick stainless steel, observing the ease of penetration, any bit travel across the steel surface, and the formation of metal chips/dust. We also noted how securely the bit was retained by the drill chuck and, when drilling by hand, how smoothly it transitioned from point penetration to the full diameter of the bit. Finally we used a bench grinder to sharpen the bits and drilled another hole with each one. Each of the sets we picked tested successfully, with the primary differences or improvements being edge retention, tip and shank design, and set configuration.
With loads of available bits for hard metal applications, finding the right drill bits for stainless steel can be challenging. We spent more than 40 hours researching the best materials and designs used to make these bits, selecting our top picks, and then testing our picks in the workshop. Read on to find out what makes a durable and effective drill bit for stainless steel, our selection criteria, and how our selections performed in testing.
Advanced cutting tools can maximize metal removal rates (MRR) when machining even the most difficult-to-machine materials. Powered by the latest CAM programs, these machining strategies are known variously as high-speed, high-efficiency, optimized roughing and also by proprietary brand names like Mastercam’s Dynamic Milling. Tools such as multi-flute, solid-carbide tools benefit from the latest advanced technologies in machine look-ahead, high-speed spindles, coatings and geometries.
Available in several grades, each with at least 10.5 percent chromium, stainless steel is popular because of its low maintenance, high sheen, and resistance to stains and rust. DIYers and trade professionals often need to drill stainless steel to complete a variety of electrical, plumbing, and automotive projects. Whether you’re expanding the size of a junction box punch-out or boring out a broken bolt, having the right drill bit matters. Drill bits built to work on softer material, like wood, won’t do the trick against stainless steel. Luckily, manufacturers design special drill bits capable of puncturing even the hardest grade of stainless steel.
Over the course of 2 days, we spent about 12 hours shop testing the drill bits we selected. After unpacking and noting the physical characteristics of each bit set and the cases they came in, we started drilling. From each set, we tested four different bits, first in a drill press for precision and accuracy, then in a cordless drill to gauge comfort and smooth operation.
We liked the compact round carry case that these bits come in. The screw-on top held securely and seemed to be watertight after we accidentally dropped it in a puddle. However, the bit-size indexing was all but impossible to read. Although the large quantity of bits makes the set heavy, this would be a good choice for carrying to project sites where precision drilling is required.
The 3-flat shank prevented bit slippage in the chuck and eliminated most snags in the drill work when excessive pressure was applied. The heavy-duty plastic carry case was easy to use and light enough to tote in a tool bag. Overall, it’s a nice all-purpose choice for everyday use with stainless steel and most other metals.
In testing, the Bosch M42 drill bits made drilling a pleasure thanks to their unique combination of design features. The M42 alloy itself allowed the bits to hold their sharp edge longer than others we tested, which meant more holes with less work stoppage to resharpen. The split-point design was easy to sharpen when needed and only required two or three additional passes on the grinder compared to M35 bits from other sets. The 3-flat shank was fast and easy to chuck securely, and we never had to worry about the bit slipping or becoming stuck in the work surface.
“In evaluating machining for large aerospace parts, for example, while I’m not a programmer, in most cases I can look at the program and tell what ought to be changed,” said Bruhis. “In the last few years between traveling and working all over the world, if I can’t review the program, I have my customer send a video of the simulation and hold an online meeting to discuss possible program modifications. Through Skype interactions, I do simulations and alter programs constantly.”
The DeWalt 14-piece Industrial Cobalt Alloy drill bit set is built for working on hard stainless steel, with features to prevent bit breakage, shank slippage, and travel on the work surface. The set includes 14 bits made of durable M35 cobalt alloy steel. It includes the most popular bit sizes from 0.0625 inch to 0.375 inch. Pilot points make it easy to start drilling precisely where the hole needs to be, while the 3-flat shank design prevents slipping in the drill chuck.
We appreciated the affordability of this kit’s overall packaging and design, which allowed the tool quality to remain high while minimizing branding and engineering costs. The bits functioned comparably to similarly designed bits from bigger brand names, with good drilling capability and an easy-to-sharpen point. We also liked that the kit includes duplicates of several smaller sizes, as they are the ones that dull easiest and are more susceptible to breaking under excessive pressure. The case does feel a bit flimsy and the size selection is somewhat limited, so this won’t be a great fit for those who require high precision. But for occasional drilling, it’s a really good deal.
Cutter paths vary and can include profiling, slotting, and pocketing. Workpieces can vary in complexity and size as well. YG-1 has tools for specific materials like titanium, Inconel or aluminum as well as general-purpose tools for smaller shops and multiple applications.
The end mills are available in four geometries: barrel-shaped, oval form, taper form and lens shape. Oval and taper form mills are suited for curved shapes such as blades or straight-walled pockets, freely engaging more of the cutting edge. Barrel design mills provide effective flank milling to the sides of spiral grooves and similar applications, according to Emuge. Lens-shaped mills excel in narrow channels or in lands on molds. Specific CAM systems software, such as Mastercam and hyperMILL, are required to support and compute the geometries.
Seco Tools has developed specific geometries, coatings, carbide substrates and edge preps for these difficult-to-machine materials. The company’s latest development in coatings is its patented HXT silicon-based coating for higher thermal resistance and abrasion resistance. “What we have found is that these same tools can be used to cut easier-to-machine metals such as tool steels, stainless steels and cast iron. So we’re now able to use these high-efficiency milling strategies to increase tool life and productivity on a broader range of easier-to-machine materials,” said Ball.
Infusing drill bits with cobalt is another way that manufacturers achieve ultrahard drill bits. High-speed steel, also known as HSS, is the most common drill bit for metal drilling. Cobalt drill bits are an extension of HSS bits. They are made with a special steel alloy that includes 5 percent to 8 percent cobalt.
In our stainless steel drilling tests, these Milwaukee bits surprised us with noticeably faster, more precise penetration into the steel. The elevated pilot point, which is visibly shorter and narrower than others tested, seemed to offer the best balance of accurate placement and rapid material removal. We also noted that the center point did not get in the way of sharpening like some of the other pilot-point bits. Plus, Milwaukee’s hard plastic carry case was our favorite of the entire test group. It held the bits more securely, offered easy-to-read size indexing, and was easy to open and close securely. If the bit size assortment were more comprehensive, this set could have been our Best Overall pick.
“Processing these materials with conventional machining processes tends to work harden them,” he explained. “Using high-efficiency milling and optimized roughing, there is a lot less heat generated because you are taking lighter radial stepovers and depths of cut (DOC), but not putting a lot of heat into the workpiece,” he said. “Where the typical solid-carbide end mill used for roughing and finishing typically had four and five flutes, with high-efficiency milling now taking over the industry we have added six-, seven- and nine-flute tools.”
Carbide is one such material found in drill bits for stainless steel. Titanium and tungsten carbide are nearly as hard as diamond, making them ideal for penetrating steel. These carbide-infused drill bits are one strong option when drilling straight into stainless steel.
Those with lingering inquiries about drill bits for stainless steel may find the info they need in the answers to these frequently asked questions. It should help folks use and maintain the best drill bits for particular projects.
We certainly appreciated that the Irwin cobalt drill bit set had the best selection of bit sizes, in tight increments of 0.015625 inch from one size to the next. It would make a great choice for anyone who requires a high degree of precision in terms of hole sizes. However, in testing we saw that the straight shanks required a little extra care when chucking to ensure a secure fit without slipping. The straight shanks also made the bit a smidge more likely to get stuck if we applied too much pressure.
It is different with PH stainless, some duplex stainless steels, and titanium alloys where speed can be increased to get more productivity out of the tool. “Duplex stainless steels that have a lot of nickel and chrome content machine more like Inconel materials because of the high nickel content. So, it’s essential in machining high-temperature alloys to understand the alloying elements in them,” he said.
These tips got into the material quickly and smoothly transitioned out to the full diameter of the bit. The edges held up remarkably well compared to M35 bits, but the tip design called for greater care when it finally came time to sharpen. We had to work slowly using extra caution to maintain the multitier tip profile.Though the thin plastic case is nothing to brag about, the size indexing was easy to read.
Titanium nitride (TiN) protects high-speed drill bits. Distinctive for their golden color, TiN-coated drill bits are ideal for high-speed drills. The coating provides the ancillary benefit of being ultradurable, making them an excellent value for consumers who intend high-frequency use.
Cycle times for five-axis machining of molds, blades and other complex aerospace and medical parts can be reduced up to 90 percent with Circle Segment solid-carbide end mills, according to Emuge Corp, West Boylston, Mass. While manufacturers performing high-speed machining may be familiar with using traditional ball nose end mills to make small stepover passes, Circle Segment end mills use high stepover passes up to 10 times greater than ball nose end mills to cut out large areas of material, maximizing efficiency and minimizing cusp height.
With the above considerations in mind, we selected the following drill bits as our top picks for drilling stainless steel. Read on to find out the details on each set, how they performed in our drilling tests, and why we included them among the best drill bits for stainless steel.
We found the 135-degree split tip to be very easy to sharpen. Also, the steel carry case proved durable and well organized with easy-to-read size indexing, although it weighed more than the heavy-duty plastic cases used by competitors. It’s probably best to keep this set in the shop and use a smaller set for traveling work.
“I talk to a lot of people in aerospace and the trend has changed in the last 10 or 15 years,” Bruhis continued. “It’s not the cost of the tool any more. Customers want to know the real cost of metal removal. There are a lot of cases where I meet with engineers or programmers and they clearly voice that they do not care about the price of the tool. Cycle time and tool life are the most important considerations.”