Stainless steel drilling problems usually show up as three separate complaints: chips wrapping around the flute and jamming the hole, the shank spinning inside the chuck under load, and the edge going dull faster than expected. Most buyers treat these as three unrelated issues. In practice, they trace back to the same two root causes — stainless steel work-hardens quickly and dissipates heat poorly — and a bit built to handle stainless addresses all three with three specific design choices rather than one.
1. Why the Chip Doesn’t Break on Its Own
Stainless steel is ductile. Left alone, it doesn’t shear into short chips the way cast iron or free-machining steel does — it deforms into a long, continuous ribbon that keeps growing as the flute turns. That ribbon does two things a shop doesn’t want: it wraps around the drill body, and it drags back across the wall of the hole it just cut, adding friction exactly where heat is already building up.
A chip breaker addresses this mechanically, not through material choice. A series of notches is ground into the cutting edge so the chip is physically interrupted as it forms, breaking it into short segments instead of one continuous strip. Shorter chips clear the flute more easily, which keeps the cutting zone from re-cutting material that’s already been removed — a common contributor to rough bore surfaces on stainless parts.
2. Why the Shank Changes Shape at 5mm
This detail gets overlooked in spec sheets but matters in daily use. Below 5mm, cutting torque is low enough that a straight round shank holds fine in a standard chuck. Above 5mm, torque climbs, and a round shank has less to grip — under load it can spin in place, chewing up the shank surface and stalling a hole that’s already started.
A tri-flat shank (three ground flats instead of a round surface) increases the contact area between shank and chuck jaws without requiring the operator to crank down harder on the chuck. That’s the practical benefit: less slip at the diameters where torque is highest, less wear on chuck jaws over time, and one less reason for a stalled cut mid-job.
3. Why M35 Is Specified Instead of Standard M2
M2 is not a poor choice for stainless — it’s a slow one. Because stainless conducts heat badly, cutting temperature concentrates at the edge instead of spreading into the workpiece, and M2 starts losing hardness once that temperature climbs. The result is edge wear that accelerates well before the bit has done its expected number of holes.
Adding cobalt (M35) raises the temperature at which the cutting edge starts to lose hardness, and increases the steel’s overall abrasion resistance. It doesn’t change how the bit cuts — it changes how long the edge keeps cutting the same way before it needs resharpening. For continuous or high-volume stainless work, that’s the variable that determines cost per hole, not the price of the bit itself.
What This Means When Comparing Suppliers
None of these three features work in isolation. A chip breaker on an M2 bit still helps chip evacuation but won’t extend edge life. An M35 bit without chip breaker geometry will hold its edge but still jam on long stainless chips. A tri-flat shank on a small-diameter bit solves a problem that doesn’t exist yet at that torque range.
When evaluating a stainless drill bit from any supplier, it’s worth asking:
• What diameter range actually needs the tri-flat shank, and is it applied only where it’s needed?
• Is the chip breaker geometry ground into the cutting edge, or just marketed as a coating effect?
• What cobalt percentage is specified, and does it match the diameter and application (sheet, plate, structural)?
These are the questions that separate a bit built for stainless from one that’s simply labeled for it.
SPECIFICATION REFERENCE
| Material | HSS-Co 5% (M35) / HSS-M2 / HSS 4341 |
| Point Angle | 130° with Chip Breaker |
| Standard | DIN 338 |
| Diameter Range | Ø1mm – 13mm (Metric) |
| Shank Type | Straight Shank (Ø1–4.9mm) / Tri-Flat Shank (Ø5mm and above) |
| Finish | Bright / Amber / Black Oxide / Black & Amber |
| Packaging | Single Size / Full Metric Set / OEM Packaging Available |
Post time: Aug-03-2026