High-Helix Drills: When Fast Helix Is the Answer

Helix Angle Basics: What the Angle Does

The helix angle of a drill describes how steeply the flutes spiral around the body. A standard jobber drill runs 25 to 30 degrees — a moderate helix that represents a compromise between chip evacuation speed, drill body rigidity, and cutting edge sharpness. A high-helix drill at 35 to 45 degrees spirals more aggressively, which changes the geometry in ways that matter significantly for specific materials.

The helix angle directly determines the rake angle at the cutting edge — the angle at which the cutting lip meets the material being cut. Higher helix angle means higher effective rake angle. High rake angles mean the cutting edge slices more aggressively, requiring less force to shear a chip of the same thickness. This is why high-helix drills tend to cut with lower thrust force than standard helix in materials where rake angle is the limiting factor — primarily soft, ductile materials where chip flow efficiency matters most.

The tradeoff: higher helix reduces the cross-sectional area of the web — the core of the drill between the flutes. A narrower web means less torsional rigidity. High-helix drills are more susceptible to twisting off under sudden load increases, harder material interruptions, or jammed chips. This brittleness relative to standard helix is why high-helix drills are reserved for specific applications rather than used universally.

Aluminum: The Primary Application for High Helix

Aluminum is the canonical application for high-helix drills. The material is soft and ductile — it shears easily with minimal force — but it produces long, gummy chips that have a strong tendency to weld to the drill flutes (built-up edge) and pack in the hole at high production rates. Standard helix drills in aluminum work acceptably at low speeds but struggle in high-volume CNC production where the chip volume per unit time overwhelms the flute's ability to evacuate it.

A 40-degree high-helix drill in 6061-T6 aluminum demonstrates the improvement clearly. The aggressive spiral creates a more efficient "chip conveyor" action — chips are pulled upward and out of the hole with each revolution rather than being pushed by chip pressure alone. Combined with polished flute surfaces, the high-helix geometry in aluminum can produce cycle times 20 to 40 percent faster than standard helix at equivalent drill life, because the higher speeds that are productive in aluminum can be run without chip packing.

Specific numbers: standard helix in 6061 runs well to 200 to 250 SFM for HSS. High-helix in 6061 can run to 300 to 400 SFM while maintaining equivalent drill life, because the faster chip evacuation reduces the thermal and adhesive loading that limits standard helix at high speeds. The increased throughput from running 40% faster at equivalent tool life represents a significant cycle time improvement on aluminum-heavy production.

7075-T6 and 2024-T4 aluminum also benefit, though the higher strength of these alloys means the rigidity tradeoff is slightly more of a concern. For 7075 production drilling, a 35-degree helix (rather than 40+) is a common compromise — enough evacuation improvement over standard helix to matter, with better rigidity than the most aggressive high-helix options.

Other Materials Where High Helix Adds Value

Beyond aluminum, high-helix geometry benefits several other material categories:

Copper and brass: Similar to aluminum in their tendency to produce long, gummy chips that adhere to tool surfaces. High-helix drills in copper significantly reduce the BUE problem. Note that some brasses (particularly leaded free-machining brass) produce short chips naturally and don't need high helix — use standard geometry there.

Soft plastics: HDPE, polyethylene, nylon in soft grades, and similar materials produce chips that pack and melt from friction heat with standard drills. High-helix geometry improves chip evacuation and reduces the dwelling that causes frictional melting. Combined with sharp geometry and appropriate speed (150 to 250 SFM for most thermoplastics), high-helix drills produce cleaner holes in soft plastics.

Soft, free-machining steels: 12L14, 1213, and other resulfurized free-machining grades produce crumbly chips that can pack in flutes at high production rates. High helix helps in these applications, though the benefit is less dramatic than in aluminum because the chip formation is already favorable.

Deep holes in any soft material: When drilling holes deeper than 5x diameter in aluminum, copper, or soft plastics, high-helix geometry is the standard choice for its evacuation advantage. Combined with through-spindle coolant (or MQL oil mist) and appropriate peck drilling strategy, high-helix drills make deep-hole production in soft materials reliably continuous rather than prone to packing failures.

When Not to Use High Helix

The rigidity tradeoff makes high-helix drills wrong for hard, interrupted, or high-torque applications:

• Steel above 30 HRC: standard or parabolic helix with appropriate cobalt grade preferred
• Stainless steel, titanium, nickel alloys: standard helix provides better rigidity for the high torque these materials generate
• Interrupted cuts (through castings with voids, plates with holes already present): standard helix survives the impact loading better
• Drills under 1/8" diameter in any material: the web area is already thin; high helix makes micro-drills dangerously fragile