Slot Drills

Slot Drills for Milling and Slot Cutting in Australian Engineering

A slot drill is a 2-flute end mill designed to plunge directly into material and cut slots, keyways, and pockets without a pre-drilled start hole. The 2-flute geometry with centre-cutting end geometry allows axial plunge cutting — the defining feature that separates a slot drill from a 4-flute end mill, which can't plunge cut reliably. AIMS Industrial stocks HSS slot drills from Sutton Tools and Bordo for Australian machining, toolmaking, and engineering customers.

Slot drill vs end mill: when to use which

• Slot drill (2-flute) — use when the cut starts in solid material (plunge entry), for keyway cutting, and for slotting where chip evacuation matters. The 2-flute geometry gives more chip clearance in the cut
• End mill (4-flute) — use when machining from an existing hole or edge (no plunge needed); provides a better surface finish on finishing passes due to more cutting edges. Not suitable for plunge cutting

Common applications

• Keyway cutting — slot drills are the standard tool for milling keyways in shafts and bores; the slot width is matched to the Woodruff key or parallel key dimension
• Pocket milling — for enclosed pockets where the cutter must enter from the top, plunge to depth, then ramp or helical interpolate to full pocket depth
• T-slot and dovetail preparation — roughing the slot before the T-slot or dovetail cutter passes
• General slotting — any through-slot where chip clearance is important

Sizes and materials stocked

Common diameters stocked range from 3mm through 25mm in standard metric steps. HSS slot drills are the general-purpose choice for steel and aluminium; TiN-coated HSS improves tool life in harder materials and production applications. For difficult-to-machine materials or high-volume work, carbide slot drills are available — enquire directly.

Cutting parameters

Slot drills require lower spindle speeds and feed rates than equivalent-diameter drills — cutting speed in steel is typically 20–30 m/min for HSS; divide by π × diameter to get RPM. Use a rigid machine setup; slot drills are more susceptible to chatter than end mills due to fewer cutting edges. Apply cutting fluid, particularly for stainless steel and harder alloys.

Related cutting tools

See also: square end mills (4-flute) for surface finishing cuts, drill bits for drilling to depth before milling, and reamers for finishing bores to tolerance.

For specific diameter, flute length, or coating requirements, contact our team.