Kennametal Carbide Drill Speeds and Feeds: What I Tell Every Machinist in a Rush

Here's the short answer: for Kennametal carbide drills, don't guess speeds and feeds. Start with the starting point in Kennametal's published data for the material you're cutting, then adjust for your machine's rigidity and coolant. The fastest way to fail an emergency job is to trust a number you once saw on a forum. Use the formula, verify the chart, and let the chips tell you the truth.

In my role coordinating emergency machining at a job shop in the Midwest, I've handled 40+ rush orders in the past year alone, including same-day turnarounds for aerospace and oilfield clients. Almost every tool failure I've seen came down to one mistake: someone guessed the feed instead of calculating it. Guessing is how a drill that should last 300 holes dies in 20.

According to Kennametal Inc.'s technical documentation, a coated carbide drill in medium steel (1045 or annealed 4140) will often start around 260-300 SFM and, depending on diameter, 0.002-0.006 in/rev. Those are starting points, not limits. The catalog was written by engineers who tested the tool; trust it more than my memory or a random blog.

Why Speed and Feed Matter

Speed (SFM or Vc) controls cutting temperature. Feed (in/rev or mm/rev) controls chip load. Too much speed burns the carbide edge. Too much feed snaps the drill. Both end the same way: a scrap part, a broken tool, and a missed deadline.

Let me rephrase that so it sticks: speed creates heat, feed creates pressure. Speed too high? You'll see burned and discolored edges. Feed too high? You'll see a nice new hole and a drill shank where the bottom edge used to be. The right combination is what produces those tight silver curls every machinist likes.

Why does everyone want to skip the math? Because it feels slow. But here's the thing: two minutes of calculation beats six hours of rework. I've seen a decimal slip in the feed rate turn a 10-minute drilling job into a three-hour repair session. That's not a cost-saving strategy.

How I Calculate Kennametal Carbide Drill Speeds and Feeds

Let's walk through a real example. Say the job needs a 3/8-inch (0.375-inch) hole in 4140 steel. A reasonable starting point from Kennametal's data might be 280 SFM and 0.003 in/rev. Here is the math:

• RPM = (SFM × 3.82) / diameter = (280 × 3.82) / 0.375 = about 2,850 RPM
• Feed rate = RPM × feed per rev = 2,850 × 0.003 = about 8.55 in/min

So I would set the program to 2,800 RPM and 8.5 in/min, then drill one test hole in a scrap block. (Should mention: that test hole is the cheapest insurance you'll ever buy.) If the chips come out as tight silver curls, the parameters are close. If they're blue or broken, lower the speed or improve coolant. If the drill squeals, lower the feed.

For metric shops, the same logic works: RPM = (Vc × 1000) / (π × D), where Vc is meters per minute and D is millimeters. Feed rate is still RPM times feed per revolution.

Starting Points I Actually Use

Here are rough starting points I've used on a rigid VMC with coolant-fed drills, for a 3/8-inch (10mm) class tool. Verify them in the current Kennametal catalog before you trust them; this is a starting direction, not gospel.

For low-carbon steel like 1018, I start around 300-350 SFM and 0.003-0.006 in/rev. For alloy steel like annealed 4140, 260-300 SFM and 0.002-0.005 in/rev. For stainless like 304, 200-240 SFM and a conservative 0.002-0.004 in/rev. For aluminum, 400-500 SFM and 0.005-0.008 in/rev. Cast iron? Somewhere in the same range as low-carbon steel, but I would still check the chart.

If this sounds like I'm hedging, I am. The exact number depends on your setup. What works at one shop may chatter at the next. That's why the test hole matters more than the spreadsheet.

My Rule for the First Hole

On a new job, I never start at the maximum recommended speed and feed. I start at about 80% of the recommended feed, run one hole, watch the load meter, and then step up. Speed stays near the recommended midpoint. This sounds slow, but it's faster than the alternative: a broken drill, an extractor tool, and a phone call to the customer explaining why the delivery will be late.

The first hole tells you a lot. The chip color, shape, sound, and the cut pressure on the machine all show up in seconds. If the load meter is bouncing hard, the feed is too high or the drill is walking. If the motor sounds strained, reduce feed. If the edge burns, reduce speed. I've also learned to check the toolholder before changing speeds and feeds: with more than 0.001-inch runout, any speed and feed will be unstable.

Why I Stopped Choosing the Cheapest Drill

I watched a buyer pick a cheaper carbide drill because the price was 15% lower. The spreadsheet said we would save $18 per part. My gut said the choice would bite us. It did. The cheaper drill needed lower speeds, which extended cycle time. Then one tool broke mid-run, and we paid $400 in rush shipping to get a replacement. The total cost of ownership (i.e., tool price plus cycle time, downtime, scrap, and shipping) ended up higher than the Kennametal drill we normally run.

Last quarter, a client called at 2 PM needing 40 pieces in 4340 steel by 10 AM the next day. They had been running a discount carbide drill at conservative speeds to avoid breakage. We switched to a coolant-fed Kennametal carbide drill, kept the speed at the low end of the range, and used the recommended feed. Cycle time dropped by 30%. There's something satisfying about finishing a rush job with time to spare, especially after a week of near-misses.

That's not a brand loyalty thing. It's a total-cost thing. The drill quote is only the first line of the real invoice. Downtime, scrap, and express shipping are the hidden lines that show up after the fact.

The value of guaranteed turnaround isn't just the speed; it's the certainty. When a rush job is on the line, knowing the drill won't quit halfway through the batch is worth more than a slightly higher tool price.

When to Adjust My Numbers

The parameters above assume a rigid setup, a stable workpiece, and decent coolant. Real shops rarely look like that. If you have through-spindle coolant, you can push feeds higher. If you don't, keep speed near the low end and reduce feed 10-20% for holes deeper than 3× diameter. If you're drilling an angled entry or a cross-hole, start at half feed until the drill is fully engaged.

Interrupted cuts? Drop speed 20%. A worn spindle or a holder that has seen better days? Drop feed. Stainless or hardened steel? Use Kennametal's material-specific recommendations, not the generic starting point. And if you're hand-feeding the spindle, stop reading this article and get a machining center.

I want to say the exact feed for a 10mm Kennametal carbide drill in 4140 is around 0.06-0.10 mm/rev, but don't quote me on that. Look it up in the current catalog before you hit the green button. Kennametal updates coatings and grades, so verify current speeds and feeds in their online calculator or latest handbook. This was accurate as of early 2025.

And if you find yourself scrolling through photos of Kennametal's facility in Orwell, Ohio, remember that the building tells you less than the tool data sheet. The geometry is fixed at the factory; the speed and feed are where you win or lose. Don't guess them.