Machinists drill materials that punish ordinary bits: stainless, tool steel, titanium and hardened alloys. The best drill bits for machinists are cobalt and solid carbide, ground with precise 135° split points and rigid geometry that hold tolerance cut after cut, load after load, without wandering or work-hardening the hole.
What to Look For
On a mill, lathe or drill press, rigidity and heat resistance decide bit life. Cobalt bits alloy roughly 5–8% cobalt into HSS, raising red hardness so the cutting edge survives the heat generated in stainless and other tough metals without losing temper. Solid carbide goes further still, staying hard at high temperatures and feed rates, but it is brittle and demands a stable, low-runout setup and correct speeds to avoid chipping. Screw-machine, or stub, length adds stiffness for accurate, chatter-free holes, while a proper point geometry keeps thrust low so the bit starts true rather than skating across the surface.
The Best Type of Bit
For everyday shop metals, cobalt is the workhorse; for high-volume production, abrasive alloys, or when surface finish and tolerance are critical, solid carbide earns its higher cost. Match the choice to how rigid your machine and workholding are, because carbide punishes flex.
- Cobalt: best for stainless, tool steel and hand-fed or less rigid setups where some flex is unavoidable.
- Solid carbide: best for hardened alloys, high feeds and tight tolerance on rigid, low-runout machines.
- Point: a 135° split point cuts on contact with low thrust and resists walking.
- Length: screw-machine length maximises stiffness and hole accuracy for precise work.
Shank and Setup Considerations
Standard jobber bits above 1/2″ often carry a reduced or 3/8″ shank so they fit smaller chucks and collets without needing a larger machine. A dedicated metalworking shank keeps larger diameters running true and lets a modest drill press tackle bigger holes. Whatever the diameter, minimise runout, use the right cutting fluid for the alloy, and hold speeds and feeds in the correct range. Carbide in particular fails fast if it is run too slow and allowed to rub, or fed too lightly, so treat the numbers as requirements rather than suggestions. Peck drilling clears chips and controls heat on deeper holes, and a spotting or pilot drill keeps a large bit from wandering as it enters. Solid workholding matters as much as the bit itself, because even flawless geometry cannot save a part that shifts under load.
Precision Starts With the Right Data
Reference charts turn guesswork into repeatable results. Confirming tap-drill and clearance sizes before you cut protects both your tolerances and your bits, and checking technical data for the alloy keeps your speeds and feeds honest. A hole drilled to the correct size the first time saves a reaming pass and a scrapped part. Our American-made cobalt and carbide bits are ground to consistent, repeatable geometry, so a size you trust today performs the same on the next run and the one after that.