In the world of metalworking and DIY, HSS (High-Speed Steel) is the gold standard for general-purpose drilling. Whether you are a hobbyist or a professional machinist at industry, understanding the nuances of HSS can save you time, money, and broken tools.
1. What Exactly is HSS?
High-Speed Steel is a carbon tool steel alloyed with elements such as tungsten, molybdenum, chromium, and vanadium.
The “High-Speed” name comes from its ability to withstand higher temperatures without losing its “temper” (hardness). Unlike standard high-carbon steel, which softens when it gets red-hot from friction, HSS maintains its cutting edge at much higher drilling speeds.
2. Common Types of HSS Drill Bits
Not all HSS bits are created equal. Depending on the alloy, they are categorized for different toughness levels:
- HSS-R (Rolled): These are heated and rolled into shape. They are the most affordable and best for general tasks in soft metals, wood, and plastic.
- HSS-G (Ground): These bits are ground from a solid blank using a CNC grinder. They have a sharper edge and higher precision, making them ideal for industrial use and harder steels.
- HSS-Co (Cobalt): Usually containing 5% to 8% Cobalt (M35 or M42 grade). These are the “heavy-duty” version. Cobalt increases the red-hardness of the bit, allowing it to drill through stainless steel and cast iron without burning out.
3. Key Geometric Features
The performance of an HSS drill bit depends heavily on two angles:
- Point Angle:
- 118°: The standard point. Great for all-purpose drilling.
- 135° Split Point: A flatter point that “bites” the material immediately. It prevents the bit from “walking” or sliding across the metal surface when you start.
- The Flutes: These are the spiral grooves. They serve two purposes: lifting chips (swarf) out of the hole and allowing coolant to reach the cutting tip.
4. Protective Coatings
To further extend tool life, HSS bits are often coated:
| Coating | Color | Purpose |
| Black Oxide | Black | Retains lubricant and prevents rust; best for general steel. |
| Titanium Nitride (TiN) | Gold | Increases surface hardness and reduces friction. |
| Titanium Aluminum Nitride (TiAlN) | Dark Purple/Black | High thermal stability; best for high-speed machining. |
5. Maintenance and Sharpening
One of the biggest advantages of HSS over Carbide is that HSS can be resharpened. When the edge becomes dull, a bench grinder or a specialized drill sharpener can restore the point.
Pro-Tip: Always use cutting fluid (coolant) when drilling metal with HSS. It reduces friction heat and prevents the cutting edge from “rounding over.”
Summary Checklist for Buying HSS
- Material: Choose HSS-Co (Cobalt) if you are drilling Stainless Steel.
- Point Type: Look for “Split Point” to avoid the need for a center punch.
- Shank: Ensure the shank fits your chuck (Straight, Hex, or Morse Taper).
At ASPTool, we provide more than just hardware; we provide the technical intelligence to help you choose the right HSS grade for any application. Contact us now to receive a free cost-per-part estimate for your next project.