CNC Striker: Classification and Application

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  Key takeaways
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  What Separates a CNC Striker from Other Milling Tools
• 3
  Classification by Edge Geometry and Helix Angle
• 4
  CNC Striker Coatings and What They Are For
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  Matching Striker Class to Material and Feature
• 6
  CNC Striker Class and Typical Application

A CNC striker sits between a general end mill and a dedicated face mill. It carries a short, rigid cutting head with a large core diameter, so it can take a heavy axial cut and still hold a straight wall. On our 5-axis and 4-axis machines we use it for shoulders, steps, and open pockets where a standard end mill would deflect.

The defining feature is the edge geometry. Most strikers run a 30° to 45° helix with a reinforced cutting edge, which trades a little sharpness for edge strength. That trade is worth it in 4140, 17-4PH, and titanium, where a thin edge chips within minutes.

Shank style matters as much as the head. A stub shank at 2× diameter gives maximum rigidity for shallow work. A long-reach shank at 6× diameter lets you reach into a deep cavity, but you must drop radial engagement to around 5% of diameter to keep chatter out.

Toolholding closes the loop. In a shrink-fit holder, runout can stay under 0.005 mm. In an ER collet chuck, expect 0.01 mm to 0.02 mm. That difference shows up directly on the wall you are cutting.

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  Heavy axial cutsLarge core diameter resists bending under high feed per tooth.
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  Straight wallsReinforced edge holds size better than a sharp general-purpose mill.
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  Deep pocketsLong-reach shanks need reduced radial engagement to stay stable.

Helix angle sets the axial force direction and the chip evacuation path. A 30° helix pushes chips up and out, which suits deep slots in aluminium and plastics. A 45° helix pulls the cut into the material and leaves a cleaner floor, so it is common on steel shoulders.

Variable helix tools stagger the flutes so the cutting forces do not line up. That kills the harmonic that causes chatter in thin walls. We keep several variable-helix strikers on the shelf for medical and aerospace parts with wall thickness under 1.5 mm.

Edge preparation is the second axis. A sharp edge cuts aluminium and brass cleanly. A honed edge, usually 0.02 mm to 0.05 mm radius, resists micro-chipping in hardened steel and cast iron. A chamfered edge sits between the two and works well on 304 and 316 stainless.

Do not mix these up. A sharp edge run in hard steel will fail at the corner within a few passes. A honed edge run in aluminium will rub instead of cut, and the surface finish will show it.

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  30° helixBest chip evacuation in aluminium, plastics, and deep slots.
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  45° helixCleaner floor and shoulder in steel and stainless.
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  Variable helixBreaks chatter harmonics in thin-wall parts.

Coating choice is a heat and wear decision. Uncoated carbide works in aluminium and copper alloys because the base material already handles the temperature and a coating can add friction. For steel, stainless, and titanium, a coating almost always pays back in edge life.

TiAlN forms an aluminium oxide layer at high temperature and holds up above 800 °C. It is the default for dry or near-dry cutting in 4140, 4340, and tool steel. AlTiN runs hotter still and suits Inconel and hardened material above 45 HRC.

DLC, a diamond-like carbon layer, has low friction and works well in aluminium and copper where built-up edge is the main problem. It does not like ferrous materials, so keep it away from steel.

We track coating against material in the job traveler. When a striker moves from 6061 to 17-4PH, the coating changes too. Skipping that step is the fastest way to burn a batch of edges.

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  UncoatedAluminium, brass, copper, and short runs in plastic.
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  TiAlN or AlTiNSteel, stainless, titanium, and high-temperature alloys.
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  DLCAluminium and copper where built-up edge is the issue.

Aluminium is the easy case. A 3-flute striker with a 45° helix and polished flutes clears chips fast at 300 m/min to 500 m/min surface speed. Watch for built-up edge on soft 6061; a light DLC coat or a higher rake angle fixes it.

Stainless 304 and 316 work-harden at the cut. A striker with a positive rake and a sharp-to-honed edge keeps the cut under the hardened skin. Feed per tooth should stay above 0.05 mm so the edge does not rub.

Titanium TC4 (Ti-6Al-4V) needs low surface speed, around 40 m/min to 60 m/min, and generous coolant. A 4-flute striker with AlTiN and a reinforced edge handles the heat. Climb milling keeps the heat in the chip instead of the part.

Thin-wall and deep-cavity parts are the hardest case. Here the striker is chosen for rigidity first: stub shank, high core diameter, variable helix. The cutting parameters follow from that, not the other way around.

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  Aluminium3 flutes, 45° helix, 300–500 m/min, light DLC if needed.
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  StainlessPositive rake, feed per tooth above 0.05 mm, keep cutting.
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  Titanium4 flutes, AlTiN, 40–60 m/min, climb mill with coolant.