Best Kennametal Grade for Milling A36 Steel: A Feeds and Speeds Checklist

The best Kennametal grade for milling A36 steel? I’ll answer that first, because I know it’s why you’re here. For an indexable milling cutter, the grade I keep in stock for A36 is KCPM25. If the setup is rigid and the cuts are mostly light finishing, KCPM15 is my pick. If you’re starting on hot-rolled plate with scale, or if the first pass hits torch-cut edges, KCPM25 is safer.

But here is the thing: the grade is only a decision point. A good grade with the wrong feed or speed will not save the job. I’ve been on the metalcutting side of machining for about 14 years, and the mistakes that stay with me are not the times I picked the wrong insert coating or edge geometry. They are the times I picked a correct grade and then asked the cutting edge to do something unreasonable.

Kennametal Feeds and Speeds: Starting Points for A36

Before I get into the grade question, let’s talk about the numbers you actually type into the machine. A36 is often called plain carbon steel, but it is softer and gumminer than alloy steels. Built-up edge is the thing that usually kills tool life, not abrasive wear. So the starting point needs a sharp geometry and a feed rate that keeps the edge cutting instead of rubbing.

These are my baseline values for clean A36, assuming a solid toolholder and flood coolant:

• Solid carbide end mill, 1/2 in., 4-flute: start around 300 SFM and 0.002 in./tooth feed. That works out to roughly 2,300 rpm and 18 IPM on a four-flute tool.
• Indexable shoulder milling cutter, 2 in. with inserts: start around 450 SFM and 0.008 in./tooth. Reduce both for the first pass if the plate has heavy scale.
• Hot-rolled A36 plate with mill scale: take the first pass at about 75% of the normal speed, and try to make that a separate scale removal pass if possible.

Why start lower? Because A36 from one steel mill can machine differently than A36 from another. ASTM A36 is a mechanical property specification, not a tight chemistry specification. One heat might cut like mild 1018; another might feel stickier and leave a smeared edge. If you treat every A36 lot as the same material, you’ll eventually be wrong.

The Best Kennametal Grade for Milling A36 Steel

For most A36 milling jobs with Kennametal inserts, my answer is KCPM25. It’s a versatile steel-milling grade that sits in the medium range: it has enough edge toughness to handle light interruptions and a coating that resists the built-up edge you get with low-carbon steel. For clean finishing passes with stable tooling, I move to KCPM15; for roughing through scale or heavy interrupted cuts, I go up in toughness rather than wear resistance.

The important part: don’t pick the grade before you know the cutter platform. Kennametal doesn’t offer every grade in every insert shape, and the same grade number can perform differently with a positive rake geometry versus a heavy roughing edge. KCPM25 is the first grade I check for A36, but I still verify the insert catalog page for the specific cutter before ordering.

The Chip Thinning Trap Nobody Mentions

The biggest mistake I see with A36 is not a grade mistake. It’s feed and speed entered without accounting for radial engagement. Here’s where I’ll confess my own problem, because I got this wrong long after I should have known better.

Eddie, the lead machinist at a shop where I worked in my earlier years, tried to warn me about chip thinning. He had a laminated binder with a Kennametal feed and speed sheet from the Millennium age. I was younger and thought my app was smarter than his paper. He said, “Then type in your radial engagement.”

I didn’t.

The cut was a shoulder milling pass with a radial engagement at 10% of cutter diameter. I used a feed rate that made sense for a full-width cut. The chip was so thin that the insert rubbed instead of cut. It made heat, the edge dulled earlier than it should have, and I scraped a part on a 40-piece order. Eddie didn’t say “I told you so.” He just reprinted the Kennametal page, circled the chip thinning note, and handed it to me.

Why does chip thinning matter here? Because when radial engagement is less than half the cutter diameter, the chip thickness is smaller than the feed per tooth. If you don’t compensate, you may be rubbing the work, especially in low-carbon steel that wants to smear. The old tables were often based on around 50% radial engagement. That’s also a key difference between the old Millennium-era sheets and Kennametal’s current feeds and speeds resources. The fundamentals haven’t changed, but the execution now accounts for toolpath behavior instead of assuming one perfect setup.

Use Kennametal’s Published Resources as the Start, Not the Final Word

I still use the official Kennametal speed and feed data. As of January 2025, the Kennametal website has product-level speeds and feeds for most milling cutters, which is more reliable than someone’s old pocket chart. But the catalog assumes a reasonably rigid machine, proper toolholding, and flood coolant. If your setup is a light-duty machine tool, or if you are using extended reach tooling, start a little lower and work up.

The other thing I do now is keep a note on the shop floor. After a tool change, I check three numbers before the cycle starts:

• SFM based on the actual cutter diameter, not the holder size.
• Feed per tooth based on the number of effective flutes.
• Radial and axial engagement, because they change the chip thickness.

If those three are right, the grade choice can do its job. If one is wrong, even the best Kennametal grade for milling A36 steel will look like junk.

A36 Grade and Speed Checklist I Use

If I were standing next to you at the machine, this is what I would check before you press green:

1. Confirm the insert or end mill grade. For indexable milling of A36, I usually run KCPM25. For finishing, KCPM15.
2. Start clean A36 at 300 SFM for solid carbide end mills and around 450 SFM for indexable milling cutters. Slow down on scale.
3. Feed enough to form a chip. Low-carbon steel is gummy, and tiny feed per tooth does not always protect an edge; it can make the tool rub.
4. Use flood coolant if it’s available and keep the coolant on throughout the cycle. Stopping the coolant mid-cut with carbide can cause thermal cycling.
5. Run one test part or one test pass. Listen for chatter, watch the spindle load, and look at chip color. A straw or light blue chip on steel tells me the edge is cutting. Blue-black chips mean I should back off speed or cooling.
6. Record the result on a job sheet. A36 from another plate may need a different number next month.

The best Kennametal grade for milling A36 steel is only a starting point, but it is a useful one: KCPM25 for general milling, KCPM15 for stable finishing, and a tougher edge for rough scale. Get the feeds and speeds right, and the same grade will last more than one job. That’s the difference between reading a number and managing a process.