The number of flutes determines the stepover percentage because it determines the chip spacing. Tool diameter also plays a role. For example, a 0.5-in.-dia. tool with 9 flutes has less chip spacing than a 1-in.-dia. tool with 9 flutes.

2. Understand the power of CAM. It is impossible to program an optimized roughing strategy manually. You need to use a programming software package that will control the cutting strategy. But not just any programming software will work; it needs to be the right software for this application. A program designed only for high-speed side milling will not perform optimized roughing.

Because they work effectively in both metal and wood, any Pro looking for a general-purpose set of hole saws should quickly fall in love with their productivity. It vastly outperforms bi-metal blades and tackles those materials carbide wood hole saws can’t (or shouldn’t) touch. You can buy kits from $105-$190

When drilling a hole with a cobalt bit, add a drop of oil on the metal to keep the cutting edge cooler as it cuts. You also want to consider placing some wood underneath the steel if possible. This lets you cut cleanly through the material and not strike a surface below which might dull the cutting edge.

Ball suggested milling chucks, shrink-fit holders, and high-precision collet chuck systems when using this milling strategy.

When we talk about drilling in hardened steel, we mean medium or high carbon steels typically made using a heat-treatment and tempering process. Hardened steels are durable and can be wear-resistant, corrosion-resistant, and abrasion-resistant. Much of the steel materials that we see used in mechanical engineering, energy generation, and transportation are basically hardened steel. The best drill bits for metal could be designed for these hardened steel applications or they might be optimized for speed in softer carbon steels.

4. Use the tooling manufacturer’s recommended cutting parameters. Do not rely on the default cutting speed and feed rate data from programming software suppliers. Cutting tool suppliers develop the recommended cutting parameters after research and through years of experience. Tool makers optimize cutting data for the tool’s design and specifications and for the material group you are working with.

“Niagara Cutter [a division of Seco] has a multiflute family of tools that is used for this type of cutting. They feature a 38-degree helix, large core diameters, and multiple flutes (6, 7, 9). The tools used for optimized roughing typically have some sort of corner protection (radius or chamfer) and are coated to provide both heat and abrasion resistance, typically an AlTiN coating,” said Bell.

You can find many types of drill bits made with an equally diverse amount of coatings and compositions. When it comes to the best drill bits for metal, however, only a few materials hold up well over time.

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The holder needs to provide less than 0.0004 in. of runout. A precise holder ensures the accuracy of the process, whereas a less secure holder will cause undesirable levels of vibration at optimized roughing’s high feed rates.

Listed in our best drill bits article, Milwaukee Red Helix cobalt bits use a variable flute design that clears away debris quickly. How quickly? About 30% faster than most other 135° split-tip bits we tested against. Their unique design not only helps them drill efficiently, but it also aids in cooling. The trade-off is that these bits thin out more towards the tip. Milwaukee countered this by making them a bit shorter than some others we’ve seen. However, they also extended the flutes lower towards the shaft. The result is a more compact bit with a similar drilling depth.

stainless can actually harden up as it heats—so drilling slowly often helps you get through the material more efficiently. Use cutting oil or similar lubricant when drilling into stainless and apply enough pressure to see a steady removal of material. Even the best drill bits for stainless steel heat up over time, so be prepared to monitor heat buildup.

Bosch CO21B 21pc Cobalt M42 Metal Drill BitFor Pros looking for a reliable kit that should last a long time while providing plenty of options, this 21-piece kit delivers.

Stainless steels are steel alloys consisting of at least 10.5% chromium and there are different grades. As a low-carbon steel, stainless steel has a natural hardness that comes without traditional hardening. Because of rust and stain resistance, good luster, and low maintenance, it has many commercial uses including cookware, cutlery, home appliances, construction fasteners, and surgical instruments.

To make it even better, you get a nice kit with clearly labeled bit sizes. The largest bits also feature the DeWalt Pilot Point which presents walking at the start of drilling.

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Our best Cobalt drill bits for metal drilling are made from an alloy of 8% cobalt (M42). You can also find these bits with a 5% cobalt blend (M35). Since the cobalt is blended into the steel, it doesn’t wear away like a titanium or black oxide coating. That also means you can sharpen them with something like the Drill Doctor 750X drill bit sharpener before having to replace them. This helps save money when you buy these more expensive bit sets. Cobalt bits are our go-to for drilling through metal—particularly hardened steel and stainless steel.

Irwin gives these bits a Speedpoint tip. It helps get the hole started quickly and reduces wandering. We also have to admit these became our best step bits for metal in part because Irwin laser-etched the measurements right on the inside of the flute. They don’t wear off quickly like other bits we’ve used.

The Milwaukee Hole Dozer with Carbide Teeth really wins for metal drilling. It can tackle stainless steel and certainly anything softer or milder than that. These are the best hole saws for metal drilling that electricians, HVAC, and/or MRO Pros can use.

Which brings us to the case. If you do a lot of drilling—the case your bits come in matters. Accessing bits can be frustrating (we’re talking to you Milwaukee!) or hugely successful—like with this Irwin three-tier swing case. We love the easy-access bits, and you can easily tell the sizes from the front of each bit. Overall, this $179 kit gives you the best drill bits for metal applications of all kinds.

Our team grabs Irwin Unibit Cobalt Step Bits for any quick thin metal drilling applications. The cobalt blend gives these bits a much longer life. Since step bits are both expensive and extremely difficult to sharpen, we like them to last as long as possible.

Sometimes you need to drill through steel…but that steel is buried in concrete. For those applications, you need something like the Diablo Rebar Demon SDS-Max and SDS-Plus bits. We like the design better than Bosch Rebar Cutters because you use the same bit to drill the hole and penetrate the rebar. With Bosch, you drill using rotary hammer mode, switch to the Rebar Cutter in rotary-only mode, and then return to your original bit to finish the hole.

Optimized roughing improves metal removal rates (Q), reduces the amount of time spent in the roughing phase, and increases tool life, all while reducing the load on the machine, according to Ball.

These bits drill quickly through concrete then continue right through rebar. You really can’t find much else on the market that competes at this point, so it’s an easy recommendation for productivity. We believe in charging your accessories to the job—so if a simple bit can save you time and money, it’s a huge win in our book. Pricing goes anywhere from $6–$206.

If you want to drill steel reliably, avoid anything made with low-carbon steel. Even generic high-carbon steel tends to work well for a little while—but quickly dulls and requires sharpening.

3. Don’t cut too deep. A cutting depth of 2xD that takes the full length of the cut in one pass is recommended. The shallow radial stepover enables the depth of the cut. A larger stepover would require a shallower depth of cut to achieve the same metal removal rates. However, a cut that is too deep, more than 3xD for example, creates cutting pressures greater than the tool can bear and causes deflection.

You can also sharpen these bits—another huge advantage. That matters once you realize cobalt drill bits cost significantly more than other types of twist drill bits. Unlike black oxide or titanium bits, you want to reserve these bits for when you need them.

Ryobi 22pc Titanium Twist Drill Bit KitHomeowners should get a lot of use from this set—and the hex shanks work well with impact drivers.

Rigid workholding also is important to minimize vibration in the part or, in the worst-case scenario, movement of the workpiece.

“Today’s CAM software can be programmed to create an optimized roughing stage that uses a large DOC and light radial engagement to maximize metal removal rates. It’s a type of milling operation that is very well suited to pocketing and side profiling,” said Jay Ball, product manager for solid-carbide end mills – NAFTA at Seco Tools.

Drill America makes M42 cobalt bits that held up really well in drilling through anything we threw at them. After testing with a multitude of materials, we selected their jobber bits as our best drill bits for hardened steel.

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The bits feature the expected 135° split point, which gives you a nice, steady, and productive drilling speed. The jobber length bits work perfectly in cordless drills for onsite drilling. They come manufactured to the National Aerospace Standard 907. Because of how hard they are, you can drill up to 30% faster than you can with conventional M2 high-speed steel bits. Drill America also doesn’t grind down the shafts on its larger bits—so you get more rigidity, but you also need a 1/2-inch chuck to drive them.

Black oxide drill bits also tend to dull quickly. We also recommend avoiding inexpensive steel drill bits that lack any sort of coating. While those bits may do well in softer steel, they can quickly dull and require frequent sharpening to continue to perform. In most cases, you get what you pay for.

If you plan on drilling hardened metal or steels, we love the Irwin 29-piece M-42 Cobalt bit kit as our best metal drill bit set. Honestly, it’s not the fastest drilling bit that gets it our nod. It has to do with the use of M42 high-speed steel and its excellent case.

“With any solid-carbide application in which you are trying to hold tight tolerances, the holders can make you or break you,” said Ball. “If you try to run these strategies and these processes in a collet that is not rigid or doesn’t contain the runout, you will struggle to achieve the metal removal rate and cycle time reduction this strategy can provide.”

Use these bits when drilling tough, high-tensile strength materials like stainless steel—or even titanium. We opted for the D/A29J-CO-PC kit. It includes 29 bits in a shatterproof case. The round case makes it simple to remove the exact bit you need.

However, whatever differences there are between the outer look or chemical composition, both hardened steel and stainless steel are quite difficult to drill into. Using a drill press is often the best way to get quality results.

With titanium nitride, you have to remember it only coats the bit. As the coating wears off the cutting edges, you pretty much have to replace them. Don’t use these bits for drilling hardened steel or stainless—not if you want them to last.

When it comes to the best value pick, we wanted a set of bits for basic metal drilling. The DeWalt DWA1240 14-pc Cobalt Drill Bit Set employs a nice cobalt blend that gives these bits more capability over titanium-coated bits. You get a nice set of 14 bits ranging from 1/16-inch to the commonly-used 3/8-inch.

Ryobi puts out tons of new products every year, covering everything from tools to lawn care and even lifestyle products. […]

According to Ball, the best use of optimized roughing is in situations that use the full flute length of the tool. Roughing long, straight walls is a good example of this.

Drill bits made with a Titanium nitride coating resist corrosion and friction. It beats black oxide because it increases surface hardness and does a better job reducing heat while drilling through metal. For metal drilling, we recommend these as the bare minimum.

We’ve been in business since 2008 covering tools, writing reviews, and reporting on industry news in the construction, automotive, and lawn care industries. Our Pro reviewers work in the trades and have the skills and experience to know whether tools can perform well in the field.

“There might be some additional corner picking that you need to get closer to near net shape before you can move on to finishing, but this strategy takes the bulk of the material out,” said Ball.

Overall cycle time is dependent on the part. If a part is near-net forged, for example, it will not require as much roughing as a solid block will. Another example is a mould cavity: It requires much more time to be spent in the finishing stage rather than the roughing stage because a smooth 3-D finish is required.

Many less expensive cobalt drill bits use M35 steel which has a 5% cobalt blend. M42 steel uses an 8% cobalt blend. This gives it a greater hardness. It also lets you drill at higher speeds than the M35. Irwin sells an M35 cobalt set as well if you don’t plan to drill hardened steel.

Today’s advanced optimized roughing is only effective if implemented properly. And while similar in nature to other strategies, optimized roughing entails specific best practices that shops must adhere to and common missteps they must avoid to achieve optimum results.

Each year, we bring in and review more than 250 individual products. Our team will put our hands on hundreds of additional tools at media events and trade shows throughout the year.

We already wrote our opinions on the best drill bits overall—covering wood, metal, concrete, and more. In this go-around, we wanted to identify the best drill bits for metal applications. That includes hardened steel, stainless steel, aluminum, and more. We even wanted to see which drill bits worked well for drilling out hardened bolts as you might find in an engine block. People also ask us about bits that handle drilling through rebar. These are the bits we turn to and should steer you in the right direction.

High-Speed Steel (HSS) Drill Bits present an upgrade over older carbon steel bits. Able to hold up better to excessive heat and wear, they make up a majority of drill bits sold on the mass market. You can use these bits for just about anything—so they serve as a jack-of-all-trades for both wood and metal applications. HSS dulls very quickly when used on more abrasive material.

DeWalt puts out tons of new products every year, covering everything from core contractor tools to specialty trade-focused ones. It […]

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“Instead of encasing the tool in 180 degrees of engagement, which creates a lot of heat and a lot of pressure, better metal removal rates are achieved with optimized roughing because machinists can take a 2xD DOC and use a 10 to 12 per cent stepover, depending on material. This means you generate less heat and have less radial engagement, which means you can accelerate feed rate and surface footage rate. This is what reduces cycle time,” he added.

Pro Tool Reviews is a successful online publication that has been providing tool reviews and industry news since 2008. In today’s world of Internet news and online content, we found that more and more professionals researched a large majority of their major power tool purchases online. That piqued our interest.

Clearly, the best drill bits for hardened metal or steel come with a cobalt blend. These cobalt drill bits use an alloy including 5%–8% cobalt. This cobalt makes up part of the steel blend, so the hardness of the bit doesn’t wear off with a coating (like titanium bits). It runs throughout the entire bit.

During the roughing phase, the vast majority of material is removed from the part, typically leaving only what is required for the finishing phase.

When it comes to the overall manufacturing process, optimized roughing can typically remove 90 to 95 per cent of the rough stock on a workpiece. This leaves only about 1 to 2 per cent of the tool diameter as finish stock for removal.

1. Use the right machine. Machines used for optimized roughing need two things: fast spindles and rigidity. The spindles must generate the necessary revolutions per minute for optimized roughing’s feed rates. The rigidity of the machine minimizes vibration and contributes to part quality.

Ever check out a “review” site and you can’t tell if they actually tested the tools or if they’re just “recommending” the Amazon top sellers? That’s not us. We won’t recommend anything unless we’d use it ourselves and we don’t care who the primary retailer is. It’s all about giving you a legitimate recommendation and our honest opinion of each product.

Thanks to the cobalt steel blend, plan on sharpening these when the tips grow dull from use. The value of this kit makes these the best drill bits for steel.

For the optimized roughing operation to be successful, a constant radial DOC must be maintained. This radial DOC also depends on the material being cut. For example, superalloys can have a radial DOC that is 5 to 7 per cent of the tool diameter, while tool steel under 50 HRC can use 7 to 10 per cent of the tool’s diameter as the radial DOC value.

The amount of stepover that can be used depends on tool diameter and the number of flutes on the tool. For example, a 6-flute, 0.5-in. end mill cutting 4140 steel can use a 10 to 12 per cent stepover. With a 7-flute tool, the stepover is only 8 per cent. Moving to a 9-flute tool reduces the stepover to roughly 3 per cent.

Walter has selected the D4120 and D3120 for use with the equally tough and wear-resistant Tiger·tec® Gold coated inserts. Users requiring high precision when drilling should select the D4120 while the D3120 is considered to be particularly economical and easy to use because it only requires one type of indexable insert.

Optimized roughing is not for every part; it’s very component driven. If a part is a complex, 3-D component, optimized roughing is not going to be the most efficient way to get the highest metal removal rate during the roughing stage. When it can be employed, however, it can have a significant effect on cycle times.

The best use of the optimized roughing technique is in situations that can use the full flute length of the tool, such as roughing long, straight walls. Photo courtesy of Seco Tools.

The end result is information you can trust because of the editorial, scientific, and real-world professional experience we collectively utilize each and every time we pick up and test a tool.

As the number of flutes increases, the stepover must decrease to maintain surface finish at faster feed rates. If the stepover is too large, feed rates must be lowered, and more heat is generated with the larger amount of metal removed in each pass. By decreasing the stepover, faster cutting speeds can be achieved. This requires more passes, but the metal removal rates are still higher than at slower speeds because of the increased feed rates.

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Spyder uses a proprietary Mach-Blue plating on its drill bits. Likely a form of Titanium Nitride and Aluminum (TiAlN) coating, it helps retain sharp cutting edges and reduce heat build-up. This should deliver faster cuts and help extend the life of the bit.

We work with more than two dozen professional contractors around the United States who review products for us on real job sites and consult with us on testing methods, categories, and weighting.

The 135° split point tip helps when starting your hole and larger sizes feature a Chip Breaker—a groove at the midpoint of the cutting edge that further reduces heat buildup. We love how quickly these bits drill and also how well they remove steel in tight, efficient spirals. The combination of the unique cutting head and the flute design landed these as our best drill bits for steel—particularly carbon steel.

“We have seen as little as a 30 per cent in cycle times and a high end of 80 per cent reduction,” said Ball. “In the upper range, the cycle time reduction also takes into account a reduction in rest roughing and semifinishing.”

Optimized roughing uses a large DOC and light radial engagement to maximize metal removal rates. Photo courtesy of Seco Tools.

That’s okay! We know personal preferences take a front seat in determining the best drill bit, and every Pro is different. Do Pro Tool Nation a favor and tell us what your top pick is and why you love it. Feel free to put it in the comments below or on Facebook, Instagram, and Twitter!

Keep up to date with the latest news, events, and technology for all things metal from our pair of monthly magazines written specifically for Canadian manufacturers!

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Looking at the best-selling metal drill bits on various trusted retailers helps when shopping. You often run into the best value, and we find the less expensive kits often find themselves at the top of these lists. We dropped links to what was at the front at the time we were writing, but they change often, so be sure to click the buttons to see what’s hot right now.

When he's not playing with the latest power tool, Clint DeBoer enjoys life as a husband, father, and is an avid reader—especially the Bible. He loves Jesus, has a degree in recording engineering, and has been involved in multimedia and/or online publishing in one form or another since 1992.

An award-winning writer and graduate of the Sheridan College journalism program, he has published articles worldwide in a variety of industries, including manufacturing, pharmaceutical, medical, infrastructure, and entertainment.