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Bi-Metal Hole Saws: How to Choose the Right Size, Teeth, and Material

Bi-metal hole saws combine HSS cutting teeth with a flexible spring steel body. Learn how to select the right tooth material, diameter, and pitch for wood, metal, stainless, and plastic applications.

By JacoTools Engineering

What Is a Bi-Metal Hole Saw?

A bi-metal hole saw combines two metals into one cutting tool: a high-speed steel (HSS) cutting edge welded to a spring steel body. The HSS teeth provide hardness and heat resistance for cutting, while the spring steel body absorbs vibration and resists cracking.

This combination makes bi-metal hole saws the most versatile hole-cutting tools available — capable of cutting wood, metal, plastic, drywall, and fiberglass with a single tool.

How Bi-Metal Hole Saws Are Made

The manufacturing process directly affects performance and longevity:

1. Tooth strip production: A strip of HSS (typically M42 or M3 grade) is precision-ground with a variable tooth pattern

2. Electron beam welding: The HSS strip is welded to the spring steel cup body using electron beam welding, which creates a narrow, strong joint without weakening the heat-affected zone

3. Heat treatment: The assembled saw is heat-treated to optimize hardness in the teeth (64-66 HRC) while maintaining flexibility in the body

4. Tooth setting: Teeth are set (alternately bent outward) to create a kerf wider than the body, preventing binding

At JacoTools, we use M42 HSS for our tooth strip — the same 8% cobalt grade used in premium twist drills. This gives our hole saws superior heat resistance compared to cheaper alternatives using M3 or standard HSS teeth.

Choosing the Right Hole Saw: Key Specifications

Tooth Material

  • M42 HSS (8% cobalt): Premium choice. Best for cutting metal, stainless steel, and demanding applications. Maintains cutting edge at higher temperatures.
  • M3 HSS: Good general-purpose option. Adequate for wood, plastic, and mild steel. Lower cost than M42.
  • Standard HSS: Budget option. Suitable for wood and soft materials only.

    • Tooth Pitch

    Tooth pitch (teeth per inch, TPI) determines what materials the saw cuts efficiently:

  • Variable pitch (e.g., 4/6 TPI): The most versatile option. Alternating tooth spacing reduces vibration and works across multiple materials. This is what most professionals choose.
  • Constant pitch: Better for specific materials but more prone to vibration and chatter.

    • Diameter Range

    Bi-metal hole saws typically range from 14mm (9/16") to 210mm (8-1/4"). Key considerations by size:

  • 14-32mm: Light-duty. Suitable for handheld drills. Used for electrical conduit, small pipe penetrations.
  • 32-76mm: Medium-duty. The most common range for HVAC, plumbing, and electrical work.
  • 76-152mm: Heavy-duty. Requires a drill press or high-torque drill. Used for large pipe penetrations and industrial applications.
  • 152-210mm: Extra-large. Drill press recommended. Used for recessed lighting, large ductwork, and industrial fabrication.

    • Cutting Depth

    Standard bi-metal hole saws offer 38-44mm (1.5-1.75") cutting depth. Deep-cut versions provide 50-75mm (2-3") depth for thicker materials. Match the depth to your application — deeper is not always better, as deeper saws are harder to control.

    Application Guide

    Wood and Drywall

    Any bi-metal hole saw handles wood easily. For clean cuts in finished surfaces, use a saw with finer tooth pitch and moderate speed (300-500 RPM for larger diameters). Back the workpiece with scrap to prevent blowout.

    Mild Steel and Iron

    Use M42-tooth saws at 50-100 RPM with cutting fluid. Let the teeth do the work — excessive pressure causes premature dulling. For sheet metal under 3mm, a step drill may be more efficient.

    Stainless Steel

    M42 teeth are essential. Run at 30-60 RPM with constant cutting fluid. Stainless work-hardens, so maintain steady feed pressure — stopping and restarting in the same cut accelerates wear.

    Plastic and Fiberglass

    Use moderate speed (200-400 RPM) with no cutting fluid. Reduce pressure to prevent melting in thermoplastics. For fiberglass, wear respiratory protection — the dust is hazardous.

    Arbor Systems

    Hole saws require an arbor (mandrel) to mount in the drill. Common systems:

  • Standard arbor with pilot drill: Most common. The pilot drill centers the saw and starts the cut. Replace pilot drills when they dull — a worn pilot causes the saw to wander.
  • Quick-change arbor: Allows swapping hole saw sizes without removing the arbor from the drill. Saves significant time when switching between sizes frequently.

    • Most hole saws 32mm and larger use a standard 1/2" arbor thread. Smaller saws may use 3/8" or proprietary mounts.

    Maximizing Hole Saw Life

    1. Use the correct RPM. Too fast overheats the teeth; too slow causes excessive tooth loading. Follow the manufacturer's speed chart.

    2. Apply cutting fluid on metal. Even a spray of WD-40 extends life significantly in steel.

    3. Clear chips frequently. Back the saw out periodically to clear the kerf. Packed chips cause heat buildup and binding.

    4. Replace pilot drills promptly. A dull pilot drill forces the saw off-center, causing uneven tooth wear.

    5. Store properly. Teeth are thin and can be damaged by contact with other tools. Use the original packaging or a dedicated case.

    JacoTools Bi-Metal Hole Saw Range

    We manufacture bi-metal hole saws from 14mm to 210mm with M42 HSS teeth and variable tooth pitch. Available individually or in professional sets with quick-change arbors. All saws are tested for tooth hardness, weld integrity, and dimensional accuracy before shipping.

    Need a custom diameter or set configuration? Contact us at info@jacotools.com.

    Tags

    hole sawsbi-metalM42 HSScutting toolsHVAC toolsmetalworking
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