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Drill Bits Torque & Rigidity

Torque Transmission & Rigidity

The torque required to drill a hole increases roughly with the cube of the diameter. A 6 mm drill in mild steel might need 2 Nm of torque. A 30 mm drill in the same material needs approximately 80 Nm. A 50 mm drill can demand over 200 Nm. This is why the shank system matters so much at larger diameters.

Straight Shank Torque Limits
A standard 13 mm 3-jaw chuck, when properly tightened with a chuck key, can transmit approximately 15–25 Nm of torque before the drill begins to slip. A 16 mm keyless chuck can manage slightly more, perhaps 20–30 Nm. This is adequate for drills up to about 13–16 mm in steel. Beyond this, slipping becomes a real risk, especially in tougher materials like stainless steel or cast iron.

Reduced shank drills (e.g., a 20 mm drill with a 13 mm shank) can technically fit in a 13 mm chuck, but the torque demands of a 20 mm hole often exceed the chuck’s grip capacity. The result: the drill spins in the chuck, the shank gets scored, and the hole is ruined. For this reason, many experienced machinists avoid reduced shank drills above 16 mm.

Taper Shank Torque Capacity

The friction-lock taper system transmits torque proportional to the taper surface area and the axial insertion force. Typical torque capacities for clean, properly seated tapers:

Morse Taper Drill Diameter Range Approx. Torque Capacity
MT1 6–13.8 mm 25–45 Nm
MT2 14–23 mm 60–120 Nm
MT3 23.2–31.5 mm 150–280 Nm
MT4 32–50 mm 350–600 Nm
MT5 51–76 mm 700–1200 Nm
These figures assume clean, oil-free taper surfaces. A contaminated or damaged taper can lose 50% or more of its torque capacity, leading to the drill spinning inside the spindle — a dangerous situation on a large radial drill press.

Rigidity Comparison
Rigidity determines hole accuracy, surface finish, and drill life. A taper shank drill seated in a matching spindle bore is inherently more rigid than the same diameter drill held in a 3-jaw chuck because:

The taper contact extends over 40–80 mm of length (depending on MT size), distributing bending loads over a large area.
There is no gap between the drill and the machine — the taper is a near-perfect fit.
The 3-jaw chuck, by contrast, contacts the shank at only three narrow lines, and the chuck body itself adds overhang length that amplifies deflection.
For production drilling of large holes (above 20 mm), the rigidity advantage of taper shank drills translates directly into longer tool life, better surface finish, and more accurate hole geometry.

Diameter Ranges & DIN Standards

The diameter range is often the simplest deciding factor. Each shank type is standardized for specific diameter bands:

Parameter Straight Shank Taper Shank
Standard Diameter Range 0.5–25 mm (reduced shank up to 30 mm) 6–76 mm
Primary DIN Standards DIN 338 (Jobber), DIN 340 (Long), DIN 1897 (Stub) DIN 345 (Standard), DIN 1870 (Extra Long)
Overlap Zone 6–25 mm — both types available, choose based on machine and application
Below 6 mm Straight shank only Not available
Above 25 mm Reduced shank available but not recommended Taper shank is the standard
For diameters in the overlap zone (6–25 mm), the choice depends on your machine. If you have a drill press with a 3-jaw chuck, use straight shank. If your drill press or lathe has a Morse Taper spindle, taper shank drills in this range offer better rigidity and are the professional choice for production work.

Key standard references:

DIN 338: The most common straight shank twist drill. Jobber length (roughly 10-12x diameter total length). Covers 0.5–25 mm.
DIN 340: Long series straight shank — same diameters as DIN 338 but approximately 40% longer flutes for deeper holes.
DIN 345: The standard taper shank twist drill. Covers 6–76 mm with MT1 through MT5. This is the workhorse of machine shop drilling.
DIN 1870: Extra-long taper shank — same MT assignments as DIN 345 but with roughly 50% longer flutes for deep-hole applications.

Machine Compatibility Guide

The machine dictates the shank type. Here is how each common machine type pairs with drill shank systems:

Machine Type Spindle Type Recommended Shank Notes
Hand Drill / Cordless Drill 3-jaw keyless chuck (10 or 13 mm) Straight shank only Max practical diameter ~13 mm. No taper bore available.
Benchtop Drill Press 3-jaw chuck on MT1 or MT2 arbor Straight shank (via chuck) Remove the chuck to use taper shank drills directly. Many users do not realize this is possible.
Floor-Standing Drill Press MT2, MT3, or MT4 spindle bore Taper shank preferred for diameters above 13 mm A 3-jaw chuck can also be fitted for small straight shank drills.
Radial Arm Drill Press MT3, MT4, or MT5 spindle bore Taper shank — the natural pairing These machines are built for large holes in heavy plate. Taper shank is essential.
Engine Lathe (tailstock) MT2, MT3, or MT4 tailstock bore Taper shank Lathes are designed for taper shank tooling. Use a chuck adapter for small straight shank drills when needed.
CNC Machining Center BT, CAT, HSK tool holders with ER collets Straight shank (held in collet or Weldon holder) Taper shank drills are incompatible with automatic tool changers. Always use straight shank for CNC.
Magnetic Drill (Mag Drill) Weldon flat shank (19 mm) or MT2/MT3 Depends on model — check spindle type Portable mag drills on construction sites often use Weldon shanks for quick change.
Pro tip: If you manage a workshop with mixed equipment, keep both types in stock for the overlap range (6–25 mm). Label storage clearly by shank type to prevent operators from trying to force the wrong drill into a machine.

Full Comparison Table
Feature Straight Shank Taper Shank (Morse Taper)
Holding Method 3-jaw chuck, collet, or Weldon holder Friction fit into taper bore + tang
Diameter Range 0.5–25 mm (reduced shank to ~30 mm) 6–76 mm
DIN Standards DIN 338, 340, 1897, 1869 DIN 345, DIN 1870
Torque Transmission Limited by chuck clamping force (15–30 Nm typical) Proportional to taper surface area (up to 1200 Nm for MT5)
Rigidity Moderate — depends on chuck quality High — continuous taper contact along 40–80 mm
Runout (TIR) 0.02–0.10 mm (depends on chuck) 0.01–0.03 mm (taper-to-bore fit)
Tool Change Speed Fast with keyless chuck; very fast with CNC ATC Slower — requires drift key ejection and manual insertion
Cost (Same Diameter) Lower — smaller shank, less material Higher — larger overall length, precision taper grinding
Ideal Machine Types Hand drills, drill presses, CNC machining centers Radial drills, lathes, milling machines, large drill presses
Best For Small to medium holes, high-volume CNC production, versatility Large holes, heavy-duty production, maximum rigidity
Slipping Risk Yes — if chuck is worn or under-tightened Very low — self-locking taper increases grip under load
FLINTOOLS Product Page HSS Straight Shank Drills HSS Taper Shank Drills

Decision Guide: When to Choose Which
Use this decision framework to determine the correct shank type for your application:

Choose Straight Shank When:
Diameter is below 13 mm — Straight shank is the only practical option for small diameters, and the full range of DIN 338/340/1897 drills is available.
Your machine has a 3-jaw chuck — Hand drills, most benchtop drill presses, and portable magnetic drills are designed for straight shanks.
You use CNC machining centers — Automatic tool changers require cylindrical shanks. ER collet or hydraulic chuck holders give excellent grip and precision.
You need fast tool changes — Keyless chucks and quick-change collet systems allow tool swaps in seconds.
Budget is a priority — Straight shank drills are less expensive per unit than equivalent taper shank drills, and the toolholding (chuck) is less expensive than maintaining taper bores.

Choose Taper Shank When:
Diameter is above 20 mm — At these diameters, the torque demands exceed what a typical 3-jaw chuck can reliably handle. Taper shank drills provide the necessary grip.
Your machine has a Morse Taper spindle — Radial arm drill presses, engine lathes, and milling machine spindles are designed for taper shank tooling. Use the system the machine was built for.
Rigidity and accuracy are critical — For production drilling where hole tolerance, surface finish, and drill life matter, the taper shank’s superior rigidity pays dividends.
You drill tough materials — Stainless steel, alloy steel, and cast iron generate high torque. The taper’s self-locking grip eliminates slipping risk.
Hole diameter is 32 mm or larger — Above this size, taper shank is essentially the only option. Straight shank drills in these diameters are either unavailable or require a reduced shank that limits performance.
The Overlap Zone: 6–25 mm
In this range, both types work. The deciding factor is your machine. If you have a choice, consider the production context:

For one-off jobs and maintenance, straight shank with a 3-jaw chuck is faster and more convenient.
For production runs of 50+ holes at 14 mm or above, taper shank on a proper drill press will give you better tool life and hole quality.
For CNC production, always use straight shank regardless of diameter.

FLINTOOLS manufactures both straight shank HSS twist drills (DIN 338 and DIN 340) and taper shank HSS twist drills (DIN 345) in M2 and M35 grades. Contact us for volume pricing or custom length requirements.

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