There’s nothing more frustrating in a machine shop—or even a home garage—than snapping a drill bit mid-job. If you're using High-Speed Steel (HSS) drill bits, this issue is common but not inevitable. The truth is, most HSS drill bit breakage comes down to user error and avoidable conditions.
Whether you’re drilling into mild steel, stainless, aluminum, or even plastic, this article will walk you through proven methods to prevent your HSS drill bits from breaking prematurely—and help you get the most out of your investment.
Before we get into the fixes, it's essential to understand the root causes. According to machining references from MSC Industrial Supply and Sandvik Coromant, the top reasons HSS bits break include:
Excessive feed pressure
Incorrect speed (RPM)
Improper tool alignment
Lack of lubrication
Overheating and work hardening
Using the wrong bit for the material
Each of these problems has a solution—let’s break them down.
Speed (RPM) and feed rate must match the material and bit size. A common mistake is drilling too fast in metal, which builds up heat and weakens the cutting edge.
| Material | RPM (for 1/4" HSS bit) |
|---|---|
| Mild Steel | 1000–1500 |
| Stainless Steel | 500–800 |
| Aluminum | 2000–3000 |
| Plastic | 1500–2500 |
Tip from Machinery's Handbook: Lower RPM and increased feed pressure are better for tough metals like stainless steel. For softer materials, you can run higher RPM but need to control heat.
Drilling dry, especially in metals, increases friction and heat. This softens the HSS cutting edge and leads to cracks or full tip breakage.
Use cutting oil for steel and stainless.
Use WD-40 or kerosene for aluminum (reduces built-up edge).
Even water-soluble coolant is better than nothing for heat control.
If your drill or the workpiece moves, it creates side-loading stress that HSS bits can’t handle.
Use a vise or clamp to hold the material.
In CNC or drill press setups, ensure collet or chuck runout is minimal.
For handheld drills, center punch the hole to guide the bit cleanly.
If you’re drilling a 10mm hole straight through stainless steel with one bit, it’s likely to break or dull quickly. Instead, start with a small pilot hole.
Start with 3–4mm, then step up gradually.
Reduces torque on the drill and heat buildup.
Helps ensure straightness and accuracy.
A dull HSS drill bit not only drills slower—it generates more friction, making it more likely to jam or snap. You can sharpen bits at home using a bench grinder or drill sharpening jig.
Reference: Practical Machinist Community & Tormek Manuals: Even a 10% asymmetry in lip angle can cause off-center drilling, which adds side load and accelerates breakage.
Excessive hand pressure is a top cause of broken bits. Especially in hard materials, the bit should gradually feed on its own when properly sharpened and lubricated.
Leaning your body weight into the drill.
Jerky starts or forcing through the last few mm.
Not all HSS bits are equal:
Standard HSS bits (118° point) are for wood and soft metals.
Cobalt HSS bits (135° split point) are better for stainless steel or hardened alloys.
Parabolic flute HSS bits are ideal for deep holes and soft chip evacuation.
Choosing the wrong type for the material increases risk of chip clogging, heat, and bit failure.
Preventing HSS drill bit breakage isn’t about buying more expensive tools—it’s about knowing how to use them right. Stick to proper speeds, cooling, setup, and sharpening routines, and your drill bits will last significantly longer.
For businesses or workshops that go through dozens of bits a month, this can mean serious savings and improved efficiency.
Contact our experts today for a free quote or technical consultation.