Two Manufacturing Approaches
Taper shank drill bits — those with a Morse taper (MT1 through MT5) instead of a cylindrical shank — are manufactured by one of two methods: CNC milling or full-body CNC grinding. The manufacturing method determines the surface quality, dimensional accuracy, concentricity, and ultimately the performance and lifespan of the finished drill bit.
This distinction is unique to taper shank drills. For straight shank (cylindrical shank) drill bits, the two competing methods are rolling (roll forging) and full-body grinding — which we cover in a separate article. Rolling cannot produce the Morse taper geometry required for taper shank drills, so the economy manufacturing method for taper shanks is milling rather than rolling.
Understanding the difference between milled and fully ground taper shank drills is essential for any buyer sourcing industrial drilling tools, because the two products look similar on paper — same nominal diameter, same DIN 345 standard, same steel grade — but perform very differently in the hole.
The Milling Process
In the milled manufacturing process, taper shank drill bits are produced in multiple discrete operations, typically on different machines. The resulting product is functional but carries the inherent limitations of each individual machining step.
Step 1: Taper Turning
The raw steel bar (typically M2 or, less commonly for milled drills, M35) is chucked in a CNC lathe. The Morse taper is turned to approximate dimensions. This is a fast operation — the lathe can produce the taper profile in 30-60 seconds — but the resulting surface carries visible concentric turning marks (feed lines) from the lathe tool. These marks are typically 0.05-0.15 mm apart and create a surface roughness of Ra 1.6-3.2 micrometers on the taper.
In some economy production lines, the taper is turned on a manual or semi-automatic lathe rather than a CNC machine, introducing additional variation in taper angle and concentricity.
Step 2: Flute Milling
The turned blank is then transferred to a CNC milling machine (or a dedicated flute milling machine). A form milling cutter — a disc-shaped tool with the profile of the desired flute cross-section — is plunged into the rotating or indexed blank to cut the helical flutes. Material is removed by the milling cutter's teeth, leaving a surface finish that reflects the tooth pitch and feed rate of the cutter.
Milled flutes have a characteristic texture: they are not rough in the aggressive sense (like a file), but they are distinctly not smooth. Under magnification, you can see individual cutter tooth marks — a regular pattern of shallow ridges spaced 0.1-0.3 mm apart. The surface roughness of a milled flute is typically Ra 1.6-3.2 micrometers — four to eight times rougher than a ground flute.
Step 3: Point Grinding
Even on milled drill bits, the point (cutting tip) is ground on a CNC or manual point grinding machine. Milling cannot produce the precise point geometry required for cutting. The point grind produces the cutting lips, clearance angles, and (if specified) the split-point modification. This is the only grinding operation on a milled drill bit.
Step 4: Heat Treatment
The completed blank is heat-treated (hardened and tempered) using the standard vacuum or salt bath process for HSS. This step is identical for milled and ground drill bits.
Characteristics of Milled Taper Shank Drills
- Flute surface roughness: Ra 1.6-3.2 micrometers (visible milling marks)
- Taper surface roughness: Ra 1.6-3.2 micrometers (visible turning marks)
- Taper concentricity to flutes: 0.03-0.06 mm TIR (because taper and flutes are machined on different machines with different setups)
- Diameter tolerance: h9 to h10 (wider than ground)
- Production speed: Fast — milling is 3-5 times faster per piece than grinding
- Typical steel grades: M2 (most common), occasionally M35
- Price point: 30-50% less than equivalent fully ground drill
The Full-Body Grinding Process
A fully ground taper shank drill bit is manufactured entirely by CNC grinding. Every surface — both flutes, both lands, the point geometry, and the Morse taper shank — is produced by precision abrasive grinding wheels on a single multi-axis CNC tool grinder or a coordinated sequence of grinding operations on a dedicated production line.
The Critical Difference: Single-Setup Precision
On a modern CNC tool grinder (Walter, ANCA, Rollomatic, or similar), the entire drill bit is ground in a single clamping. The machine grinds the flutes, the lands, the point geometry, and the Morse taper without removing the workpiece from the collet. This means every surface is referenced to the same rotational axis — the concentricity between the taper and the flutes is inherent to the process, not dependent on transferring the part between machines.
This single-setup approach is the fundamental reason why fully ground taper shank drills are more accurate than milled ones. The taper and flutes are geometrically guaranteed to share a common axis because they are ground on the same axis.
Surface Finish
CNC grinding wheels produce dramatically smoother surfaces than milling cutters. A ground flute has a surface roughness of Ra 0.4-0.8 micrometers — a mirror-smooth, glassy finish that you can feel immediately when you run your fingernail along it. The Morse taper is ground to an equally smooth finish, ensuring full-contact seating in the machine spindle with maximum friction (holding force) and minimum vibration.
Dimensional Accuracy
CNC grinding achieves tighter tolerances than CNC milling because the grinding process removes material in very small increments (micrometers per pass) and the abrasive wheel can be dressed to micron-level precision. The result:
- Diameter tolerance: h8 (e.g., 20.000 mm +0 / -0.033 mm)
- Taper runout (TIR): less than 0.02 mm
- Taper angle accuracy: conforms to DIN 228 within ±0.005 mm per 100 mm of taper length
- Flute symmetry: both flutes are ground in the same operation, ensuring equal depth, equal width, and equal helix angle
Characteristics of Fully Ground Taper Shank Drills
- Flute surface roughness: Ra 0.4-0.8 micrometers (glassy smooth)
- Taper surface roughness: Ra 0.4-0.8 micrometers (precision ground to DIN 228)
- Taper concentricity to flutes: less than 0.02 mm TIR (single-setup grinding)
- Diameter tolerance: h8 (tight)
- Production speed: Slower — 3-5 times longer per piece than milling
- Typical steel grades: M2, M35 (cobalt)
- Price point: 30-50% more than equivalent milled drill
Key Differences Compared
The following table summarizes the measurable differences between fully ground and milled taper shank drill bits. These are not theoretical — they are the values we routinely measure in our quality control laboratory on production batches.
| Parameter | Fully Ground | Milled |
|---|---|---|
| Flute Surface Roughness (Ra) | 0.4 - 0.8 µm | 1.6 - 3.2 µm |
| Taper Surface Roughness (Ra) | 0.4 - 0.8 µm | 1.6 - 3.2 µm (turning marks) |
| Taper-to-Flute Concentricity (TIR) | ≤ 0.02 mm | 0.03 - 0.06 mm |
| Diameter Tolerance | h8 | h9 - h10 |
| Taper Accuracy (DIN 228) | ±0.005 mm / 100 mm | ±0.01 - 0.02 mm / 100 mm |
| Chip Evacuation | Excellent — smooth flute flow | Moderate — milling marks impede flow |
| Taper Seating Quality | Full contact — maximum holding torque | Partial contact — turning marks reduce grip |
| Tool Life (relative, steel) | Baseline (100%) | 60-75% of ground |
| Hole Position Accuracy | High — low runout, balanced geometry | Moderate — higher runout causes wander |
| Vibration Level | Low — precise concentricity | Higher — taper misalignment amplifies |
| Manufacturing Speed | Slower (3-5x longer per piece) | Faster |
| Unit Price (relative) | Higher (30-50% premium) | Lower (economy positioning) |
How to Identify: Ground vs Milled
Distinguishing a fully ground taper shank drill from a milled one is straightforward once you know what to look for. These identification methods work in the field, at incoming inspection, or on the factory floor.
Method 1: The Fingernail Test (Flute Surface)
Run your fingernail along the inside of one flute, from the shank end toward the point. On a fully ground drill, the flute feels glassy smooth — your fingernail glides without any perceptible texture. On a milled drill, you can feel a distinct texture — a series of fine ridges left by the milling cutter teeth. Under a magnifying glass (10x), the milling marks are clearly visible as parallel lines running across the flute.
This is the fastest and most reliable field test. It requires no equipment and takes under two seconds.
Method 2: Inspect the Morse Taper Surface
Examine the Morse taper shank under good lighting. A fully ground taper has a uniformly smooth, matte finish with no visible tool marks — it reflects light evenly. A milled (turned) taper shows concentric ring marks — these are the feed lines from the lathe turning operation. The rings are typically spaced 0.05-0.15 mm apart and are visible to the naked eye under direct light.
A taper with turning marks will not seat as firmly in the machine spindle as a ground taper. The reduced contact area means less friction, which translates to less holding torque and increased tendency for the taper to slip or pull out under heavy cutting loads.
Method 3: Measure Total Indicated Runout (TIR)
For objective, repeatable verification — especially for incoming quality inspection of bulk orders — measure the total indicated runout using a V-block, a Morse taper sleeve (matching the drill's taper), and a dial indicator with 0.001 mm resolution.
- Insert the drill's Morse taper into the matching sleeve (simulating machine spindle fitment).
- Place the drill in V-blocks supporting the fluted section.
- Position the dial indicator at the cutting diameter, near the point.
- Rotate the drill one full revolution and record the total indicator movement (TIR).
Results:
- Fully ground: TIR typically 0.01-0.02 mm
- Milled: TIR typically 0.03-0.06 mm, sometimes worse
A TIR above 0.03 mm is a strong indicator of a milled or poorly ground drill. For production drilling in steel, the maximum acceptable TIR is 0.03 mm — anything above this will produce oversized holes, premature wear, and vibration.
Method 4: Check the Cutting Edge
Under magnification, examine the transition where the flute meets the land (the narrow strip of cylindrical surface between the flutes). On a fully ground drill, this transition is a crisp, well-defined edge. On a milled drill, the transition may be slightly rounded or irregular because the milling cutter cannot produce as sharp a land edge as a grinding wheel.
Why It Matters in Production
The differences between milled and fully ground taper shank drills may seem modest on a specification sheet — a few hundredths of a millimeter of runout, a few micrometers of surface roughness. In production drilling, these small differences compound into significant performance gaps.
Oversized Holes
A taper shank drill with 0.05 mm of runout will cut a hole approximately 0.05 mm larger than its nominal diameter. For a 20 mm drill, this means holes at 20.05 mm — outside the h8 tolerance band. In a production run of 500 bolted assemblies, this means 500 oversized holes that may require rework, oversize bolts, or rejection. A fully ground drill at 0.02 mm runout produces holes at 20.02 mm — well within tolerance.
Vibration and Chatter
Runout causes the drill to orbit around the intended hole center rather than rotating on-center. This orbital motion generates vibration that is amplified by the length of the taper shank drill (which is inherently longer than a straight shank drill of the same diameter). Vibration causes chatter marks inside the hole (poor surface finish), accelerated wear on the cutting edges, and increased stress on the machine spindle bearings. Over thousands of holes, this accelerated wear shortens both tool life and machine life.
Chip Evacuation Failure
Taper shank drills are used for larger diameters (13 mm and above) and deeper holes where chip evacuation is already challenging. The rougher flute surface of a milled drill increases friction on the chip-flute interface, slowing chip flow and increasing the risk of chip packing. In deep holes (depth-to-diameter ratio above 3:1), this can cause the same thermal death spiral described in our fully ground vs rolled article — packed chips, rising temperature, softened cutting edge, and eventual bit failure.
Taper Seating and Holding Torque
The Morse taper interface relies on friction between two precision-ground conical surfaces to transmit torque from the machine spindle to the drill bit. When the taper surface has turning marks (as on a milled drill), the contact area is reduced — the drill sits on the peaks of the turning marks rather than making full-surface contact. This reduces the holding torque, meaning the drill is more likely to slip in the spindle during heavy cuts, or the taper may loosen and pull out when retracting from a deep hole.
The Cost Calculation
A milled taper shank drill might cost 30-50% less than a fully ground equivalent. But in production drilling (100 or more holes per day), the economics shift rapidly:
- Tool life: Fully ground drills last 25-40% longer than milled drills of the same steel grade, because smoother flutes reduce cutting temperature and even wear distribution from lower runout extends edge life.
- Rework: Oversized holes from high-runout milled drills cause rework on bolted and press-fit assemblies. At $5-20 per rework (depending on complexity), a few dozen bad holes wipe out the purchase price savings.
- Downtime: Taper slippage incidents require stopping the machine, cleaning the taper, and reseating the drill. Each incident costs 5-15 minutes of production time.
For occasional, low-volume drilling in a maintenance workshop, a milled taper shank drill is an acceptable compromise. For production drilling — any environment where the drill runs daily and hole quality matters — fully ground is the only rational choice.
The Zhonghuan Approach
Zhonghuan defines taper shank drill projects around documented M2 and M35 cobalt requirements. Ground or milled process, point geometry, finish, and inspection scope are confirmed during RFQ; economy positioning is not presented as a professional metalworking line.
This is a deliberate product strategy, not a manufacturing limitation. Our customers — industrial distributors, OEM tool brands, and production facilities — source taper shank drills for serious metalworking applications. A taper shank drill is, by definition, an industrial tool intended for stationary machines drilling steel, cast iron, and alloys. Supplying a milled economy product for this application segment would compromise our customers' production quality and undermine their trust in Zhonghuan as a supplier.
Our Grinding Process
For confirmed ground taper-shank programs, Zhonghuan uses CNC tool grinders with the following process:
- Raw material: M2 (6542) or M35 (6542Co5) round bar, certified by steel mill spectral analysis.
- Heat treatment: Vacuum hardening and triple tempering to HRC 63-65 (M2) or HRC 65-67 (M35).
- Taper grinding: The Morse taper is CNC-ground to DIN 228 specification with surface roughness Ra below 0.8 micrometers.
- Flute grinding: Both flutes are ground in a single setup, ensuring symmetry and concentricity. Target surface roughness: Ra 0.4-0.8 micrometers.
- Point grinding: 135-degree split point for M35 cobalt, 118-degree or 135-degree for M2 (customer specification).
- Quality inspection: 100% inspection of diameter, total length, runout (TIR less than 0.02 mm), and hardness for every production batch.
The result is a taper shank drill that seats firmly in the spindle, runs true, evacuates chips cleanly, and delivers consistent hole quality across thousands of holes. This is what professional buyers expect from a taper shank drill — and it is what we deliver.
View our complete range of fully ground taper shank HSS drill bits, or contact our sales team for samples, pricing, and technical specifications.
Note: Taper Shank vs Straight Shank Terminology
This article covers taper shank drill bits specifically — tools with a Morse taper (MT1 through MT5) designed for drill press spindles, lathe tailstocks, and milling machine spindles. The two competing manufacturing methods for taper shank drills are milling (economy) and full-body grinding (premium).
For straight shank drill bits (cylindrical shank, held by a chuck), the two competing manufacturing methods are different: rolling (roll forging) is the economy method and full-body grinding is the premium method. Rolling cannot produce a Morse taper, which is why it does not appear in the taper shank category.
| Drill Type | Economy Method | Premium Method | Detailed Article |
|---|---|---|---|
| Straight Shank (DIN 338/340) | Rolling (Roll Forging) | Full-Body Grinding | Fully Ground vs Rolled |
| Taper Shank (DIN 345) | CNC Milling | Full-Body Grinding | This article |
The key takeaway: milled is not the same as rolled. They are different processes applied to different product types. The only thing they share is that both are the economy alternative to full-body grinding in their respective categories. If you encounter a supplier describing a taper shank drill as "rolled," they are either using incorrect terminology or misrepresenting the product — rolling cannot produce a taper shank drill.
Related Procurement Programs
If you are sourcing this product line for a distributor, importer, or private-label channel, these OEM and wholesale programs cover the procurement questions buyers usually ask next.
- HSS Twist Drill Bits Wholesale & OEM Supply for Metalworking Channels — HSS twist drill bit wholesale and OEM supply for importers, industrial distributors, and private-label brands: M2, M35 cobalt, DIN 338, DIN 345, black oxide…
- Metalworking and Sheet Metal Drilling Matrix — A procurement matrix for steel fabrication, electrical panels, HVAC sheet metal, and automotive sheet repair: HSS twist drills, M35 cobalt, taper shank drills…
- Taper Shank Drill Bits for Structural Steel Bolt Holes -- H-Beam, I-Beam & Connection Drilling — HSS taper shank drill bits (MT1-MT5, 14-50 mm) for drilling structural steel bolt holes in H-beams, I-beams, channels, and angles.
