A centre drill bit creates the precise 60° countersunk pilot hole that supports a workpiece between lathe centres. It is the first tool used on the lathe before any turning, facing or boring — the small conical hole it produces in the end of the shaft is where the dead centre or live centre in the tailstock seats. Without that centre, the workpiece walks, vibrates, runs out of round, and finishes as scrap. With it, the part runs true to a few thousandths regardless of length, and every subsequent operation is referenced to that one centre.
The centre drill is a small but specific cutting tool — a stepped two-diameter bit with a small pilot tip and a 60° countersink shoulder. It looks like a stubby drill bit, but it has a different job from a spot drill, a different size convention from a twist drill, and a different governing standard. Confusing it with a spot drill is the most common mistake on CNC machines, and confusing it with a "self-centering drill bit" (a hinge-drilling tool, sold by the same name in cabinet-making contexts) is the most common buying error. This guide separates the two, explains every sizing convention used in Australian workshops (DIN 333 metric and ANSI B94-11 imperial), and covers every workshop application from lathe tailstock work to mill spotting to drill press pilot drilling.
For Australian workshops, AIMS Industrial stocks the full centre drill range — Sutton Tools D136 (Australian-made, ANSI B94-11 HSS), D135 (DIN 333 A type HSS), D318 / D319 (carbide and TiCN-coated for hardened steel and stainless), Bordo HSS centre drills and 5-piece sets, plus SECO Minimaster indexable centre drilling inserts for production work. The full AIMS centre drill range covers every common size from Ø 1.6 mm DIN 333 through to large carbide and indexable variants.
What a centre drill does — and where it earns its keep
A centre drill produces the conical 60° hole used to support a workpiece between lathe centres. The hole is a precise feature: the 60° angle matches the 60° angle of the live centre or dead centre in the tailstock, so the workpiece rotates on a true point with minimum runout. The pilot tip on the centre drill bit (the small cylindrical extension below the 60° shoulder) creates a tiny clearance below the centre point so the centre does not bottom out — it bears only on the conical 60° face.
The centre drill has three roles in a typical workshop:
- Lathe tailstock support hole — the primary purpose. Drilled into the end of a shaft, gear blank or any long workpiece before turning. Holds the part rigid for facing, turning and threading.
- Drill pilot starting hole — particularly on hand-fed drill presses without rigid spindle alignment. The centre drill's stiffness (from the large body and short overall length) produces an accurate starting indent that a follow-up twist drill picks up cleanly.
- Stepped pilot hole production — for fasteners requiring a 60° countersink (a smaller part of its use, but valid).
The geometric magic in a centre drill is the body diameter (D2) compared to the cutting pilot diameter (d1). For a Sutton D135 1.6 mm, the pilot is 1.6 mm but the body is 4.0 mm — a 2.5× ratio. That heavy body resists deflection on entry, so the small pilot tip locates accurately rather than wandering. As Adam Savage put it in his shop video on centre drills: "the big fat shoulder prevents it from flexing like a normal drill bit, ensuring a perfectly centered hole." That stiffness-to-pilot-size ratio is the defining feature of the tool.
Centre drill vs spot drill — the most important distinction
This is the most common question on centre drills, the most common cause of mis-buying, and the source of more 130+ comment Reddit threads than any other machining topic. The two tools look similar and produce indents that look similar, but they are designed for different purposes:
| Property | Centre drill | Spot drill |
|---|---|---|
| Primary purpose | 60° conical hole for lathe tailstock support | Precise location indent for a follow-up twist drill on CNC |
| Tip geometry | Small pilot tip extending from a 60° shoulder | No pilot — single point at the matching angle of the follow-up drill |
| Standard angle | 60° (matches lathe centre) | 90°, 118° or 140° (matches twist drill point angle) |
| Stiffness | Stiff body but fragile pilot tip — pilot breaks easily | Very stiff — short, no pilot, full body to point |
| Speed (RPM) | Two correct speeds — one for the pilot tip, one for the body | One correct speed — tip and body run at the same surface speed |
| Use on CNC | Workable but suboptimal — pilot tip is fragile under power | Ideal — spot drill is the modern CNC starting tool |
| Use on lathe | The standard tool — what it's designed for | Cannot produce a 60° centre hole — wrong tool for lathe work |
| Use on manual drill press | Excellent — stiffness compensates for chuck runout | Excellent — also a good choice |
The Practical Machinist forum consensus across multiple long threads: use a centre drill for lathe tailstock work, use a spot drill for CNC location starts. The centre drill on CNC works but is not optimal — the small pilot tip cannot be run at the correct surface speed for the body, so either the tip rubs (and breaks) or the body chips. Spot drills solve this by removing the pilot entirely. For hobby and home shop work where one tool serves both purposes, the centre drill is acceptable for everything; for production CNC, the spot drill earns its place.
Centre drill is NOT a "self-centering drill bit"
An expensive buying mistake at hardware stores in Australia: typing "centre drill bit" into a retailer search and getting back results for self-centering drill bits — a completely different tool used for cabinet making and hinge installation, not lathe work.
| Tool | Purpose | Where used |
|---|---|---|
| Centre drill | Produces 60° conical hole for lathe tailstock support; stepped two-diameter body with small pilot | Metal lathe, milling, drill press — engineering and machining |
| Self-centering drill bit (Vix bit, hinge bit) | Drills a centred pilot hole through a fixed jig — the spring-loaded sleeve centres on the screw clearance hole and the inner drill bit follows | Cabinet making, hinge installation, joinery — woodworking |
If you need to drill the pilot hole for a hinge screw on a kitchen cabinet, you want a self-centering drill bit (Vix bit). If you need to put a 60° centre on the end of a shaft to mount it between lathe centres, you want a centre drill. They are not interchangeable, do not produce the same hole, and are sold under similar names by different specialist suppliers. Confirm which you actually need before ordering — particularly important when buying from general hardware (Bunnings, Total Tools) versus engineering tool suppliers (AIMS Industrial, Hare & Forbes, Sutton Tools).
DIN 333 forms — A, B and R
The international standard for centre drill geometry is DIN 333. It defines three forms — A, B and R — that differ in the shape of the countersink shoulder and the protection given to the centre hole during use. The form is selected based on whether the centre hole is exposed to surface damage during subsequent operations.
| Form | Geometry | Use |
|---|---|---|
| DIN 333-A | 60° pilot tip + 60° countersink only — no protective outer angle | The standard form. Used when the centre hole will not see surface damage during subsequent operations. Most common in production. |
| DIN 333-B | 60° pilot tip + 60° countersink + 120° outer protective chamfer | Used when the workpiece end face must be protected from accidental damage during machining. The outer 120° chamfer creates a recessed centre that is shielded by the surrounding face. Standard for precision shaft work where the centres must remain undamaged for finishing. |
| DIN 333-R | Curved (radius) profile instead of conical — no straight 60° face | Used on hardened or surface-ground centre holes. The radiused profile reduces stress concentration and provides a smoother bearing for the lathe centre when the workpiece is to be ground. Standard for grinding work and high-precision shafts. |
The corresponding DIN standard for the centre HOLE itself (the feature in the workpiece) is DIN 332-1 — it specifies the matching dimensions A, B and R for the receiving end. A DIN 333-A centre drill produces a DIN 332-1 type-A centre hole; a DIN 333-B drill produces a type-B hole. The pairing matters when reading a drawing — if the drawing specifies a DIN 332-1 type-B centre, use a DIN 333-B drill.
For most Australian workshop work, DIN 333-A is the default. DIN 333-B is specified on toolroom and precision shaft drawings where the centres must be preserved between operations. DIN 333-R is specialty for grinding work.
DIN 333 metric centre drill sizes
DIN 333 specifies the standard metric sizes — designated by the pilot diameter (d1) with the body diameter (D2), pilot length (l1) and total length (L) all defined for each size. The full DIN 333 size series:
| Pilot Ø d1 (mm) | Body Ø D2 (mm) | Pilot length l1 (mm) | Total length L (mm) |
|---|---|---|---|
| 1.0 | 3.15 | 1.3 | 31.5 |
| 1.25 | 3.15 | 1.6 | 33.5 |
| 1.6 | 4.0 | 2.0 | 35.5 |
| 2.0 | 5.0 | 2.5 | 40.0 |
| 2.5 | 6.3 | 3.1 | 45.0 |
| 3.15 | 8.0 | 3.9 | 50.0 |
| 4.0 | 10.0 | 5.0 | 56.0 |
| 5.0 | 12.5 | 6.3 | 63.0 |
| 6.3 | 16.0 | 8.0 | 71.0 |
| 8.0 | 20.0 | 10.1 | 80.0 |
| 10.0 | 25.0 | 12.8 | 90.0 |
Source: DIN 333 sheet 1, type A. The pilot diameter is the working size that determines the centre hole. The body diameter sets the maximum countersink diameter, and the total length determines reach into the workpiece.
For Australian general workshop use, the most common DIN 333 sizes stocked are 1.6 mm, 2.0 mm, 2.5 mm, 3.15 mm and 4.0 mm — they cover the shaft sizes encountered in most fitting and lathe work. The larger sizes (5 mm and above) are used for heavier shafts and are less commonly stocked.
ANSI B94-11 imperial centre drill sizes — the # number system
The American imperial standard ANSI B94-11 specifies centre drills by a number designation from #00 (smallest) through to #8 (largest). Each number corresponds to a specific pilot diameter and body diameter combination, and the number is what's stamped on the tool. This is the standard used by Sutton Tools D136 series and stocked widely in Australia for use on imperial-spec equipment.
| ANSI # | Pilot Ø (in) | Body Ø (in) | Total length (in) |
|---|---|---|---|
| #00 | 1/32 | 1/8 | 1-1/8 |
| #0 | 1/32 | 1/8 | 1-1/4 |
| #1 | 3/64 | 3/16 | 1-1/4 |
| #2 | 5/64 | 1/4 | 1-7/8 |
| #3 | 7/64 | 1/4 | 2 |
| #4 | 1/8 | 5/16 | 2-1/8 |
| #5 | 3/16 | 7/16 | 2-3/4 |
| #6 | 7/32 | 1/2 | 3 |
| #7 | 1/4 | 5/8 | 3-1/4 |
| #8 | 5/16 | 3/4 | 3-1/2 |
Source: ANSI B94-11 (combined drills and countersinks). Note that #00 and #0 share the same pilot and body diameters — they differ only in total length.
The standard 5-piece centre drill set in Australian workshops (Sutton D136SCD1, Bordo, Maxigear) covers #1 through #5 — the range used for most shaft work between roughly 6 mm and 50 mm shaft diameter. Smaller (#00 / #0) and larger (#6 / #7 / #8) sizes are sold individually.
Materials and coatings
| Material / coating | Strengths | Limitations | Typical use |
|---|---|---|---|
| HSS (M2 / M7) | Tough, resharpenable, low cost. The default for general workshop use. | Pilot tip breaks under heavy feed or hard material. Limited heat resistance. | General fitting, lathe work in carbon steel, brass, aluminium, cast iron. Sutton D135 (DIN 333), Sutton D136 (ANSI B94-11), Bordo HSS sets. |
| HSS-E / Cobalt (M35) | Higher heat resistance — handles stainless steel and tougher alloys. Longer tool life in production. | Slightly more brittle pilot tip than plain HSS. Cost premium. | Stainless steel work, abrasive cast iron, low-volume production runs. |
| Solid carbide (VHM) | Cuts hardened steel and surface-hardened materials (Rc 45+). Long tool life. Higher RPM capability. | Extremely brittle pilot tip — breaks instantly under shock load or runout. Cost 5–8× HSS. | Production work in hardened steel; surface-hardened workpieces (gun receivers, hardened shafts). Sutton D318 (VHM Bright). |
| Solid carbide TiCN-coated | TiCN coating reduces friction, extends life by 25–40%, suits abrasive materials | Same brittleness as uncoated carbide. Higher cost. | Abrasive cast iron, surface-hardened steel, production work where tool life is critical. Sutton D319 (VHM TiCN). |
| Indexable insert (carbide) | Replaceable insert — body lasts indefinitely, only the cutting tip is consumable. Suits high-volume production. | Cost barrier — body and insert system not economical for low volume. | CNC lathe production, where centre-drilling thousands of parts. SECO Minimaster T60M (90° SIG and 120° SIG variants). |
For one-off Australian workshop centre drill purchase, HSS in DIN 333 form A or ANSI B94-11 covers 90% of work. Step up to cobalt for stainless. Step up to solid carbide only for hardened work or production where the tool-life economics justify the cost.
How to use a centre drill on a lathe
The standard lathe centre-drilling procedure for an end of a shaft to be turned between centres:
- Face the end of the workpiece first. A flat, square end face gives the centre drill a clean starting surface. Skip this step and the centre drill walks off the irregular cast or sawn end.
- Mount the centre drill in the tailstock chuck. Use a Jacobs chuck on the tailstock Morse taper, with the centre drill held in the chuck. Confirm the chuck runs true — even small runout causes the pilot tip to break.
- Set the spindle speed. 1000–1500 RPM is typical for a #2 or #3 centre drill in carbon steel — see the speeds table below for size-specific values. The pilot tip wants higher surface speed than the body, but the body's speed is what limits the tool — run too fast and the body burns; too slow and the pilot rubs.
- Apply cutting fluid generously. Cutting oil (general purpose) for steel; soluble coolant for stainless; kerosene for aluminium. The pilot tip is fragile and runs hot — lubrication is non-negotiable.
- Feed the centre drill in slowly by hand. Use the tailstock handwheel for controlled feed. Aim for a consistent chip — smooth feed, no pulsing.
- Drill to the depth where the 60° countersink is half-formed. The correct depth: when the 60° body section is engaged about half its length. This produces a countersink with the correct bearing surface for the live or dead centre. Going deeper engages the full body and may chamfer the workpiece end; going shallower leaves the centre too small to support the workpiece.
- Withdraw the centre drill. Retract by reversing the tailstock handwheel, with the spindle still running. Clean the pilot tip and inspect for chips before storing.
How to use a centre drill on a mill or drill press
On a mill or drill press, the centre drill is used to start a precise location hole before a follow-up twist drill. The technique:
- Locate the spindle over the marked centre. Use a centre punch indent for hand-drill work, or a co-ordinate move on a CNC.
- Mount the centre drill in the chuck or collet. ER collet is preferable for precision work — the chuck adds runout that the fragile pilot tip cannot tolerate.
- Set the spindle speed. 1000–1500 RPM for a #2 in steel (smaller for smaller sizes — see speeds table).
- Apply cutting fluid. Generous oil or coolant.
- Feed in only as far as the 60° shoulder begins to engage. On a mill or drill press where the centre drill is followed by a twist drill, you only need the indent — not a full centre hole. Stop before the body section enters significantly.
- Retract.
- Follow with a twist drill at the appropriate speed. The follow-up drill picks up the centre-drilled indent and runs true.
How deep should I centre drill?
One of the most common practical questions on lathe work — and the answer depends on what you need from the centre hole.
| Application | Depth target | Why |
|---|---|---|
| Lathe tailstock support — light cuts | Drill until the 60° shoulder is about 1/3 engaged | Sufficient bearing surface for the centre; minimum material removal from workpiece end |
| Lathe tailstock support — heavy cuts, long workpieces | Drill until the 60° shoulder is about 1/2 to 2/3 engaged | Larger countersink area distributes load and resists workpiece walking |
| Drill press / mill location pilot | Just enough to break the surface (1–2 mm depth typical) | The follow-up twist drill needs only an indent to locate, not a full countersink |
| Production CNC | Use a spot drill instead — it does the same job better at one correct speed | The centre drill's small pilot is the limiting factor on CNC speeds and feeds |
| Surface-hardened workpiece | Carbide centre drill, light depth, low feed — or pre-spot with a spot drill | Hardened material breaks the HSS pilot tip immediately |
The Practical Machinist rule of thumb for shaft centre-drilling: the countersink diameter should be 60–80% of the shaft diameter for medium-duty work, scaling up to 100% (countersink edge meeting shaft outer diameter) for heavy cuts on long shafts. The exact depth that produces this countersink diameter varies by centre drill size — a #2 centre drill drilled until the body shoulder fully engages will produce a countersink of about 5/8" (15.9 mm), suitable for shafts up to about 25 mm diameter.
Centre drill speeds and feeds
Centre drill speeds are usually expressed as spindle RPM rather than surface speed because the dual-diameter geometry makes surface speed ambiguous. The table below shows recommended starting RPMs for common centre drill sizes in common materials. Increase speed for soft materials (aluminium, brass), decrease for hard materials (stainless, hardened steel) and use carbide for the hardest materials.
| Centre drill size | Mild steel HSS | Stainless HSS-E | Aluminium HSS | Hardened steel (carbide) |
|---|---|---|---|---|
| #1 (3/64") / DIN 333 1.6 mm | 1500–2000 RPM | 900–1200 RPM | 2500–3500 RPM | 3000–4000 RPM |
| #2 (5/64") / DIN 333 2.0 mm | 1200–1500 RPM | 700–1000 RPM | 2000–2800 RPM | 2500–3500 RPM |
| #3 (7/64") / DIN 333 2.5 mm | 1000–1300 RPM | 600–800 RPM | 1700–2400 RPM | 2200–3000 RPM |
| #4 (1/8") / DIN 333 3.15 mm | 800–1100 RPM | 500–700 RPM | 1400–1900 RPM | 1800–2500 RPM |
| #5 (3/16") / DIN 333 4.0 mm | 600–800 RPM | 400–600 RPM | 1100–1500 RPM | 1400–2000 RPM |
| #6 (7/32") / DIN 333 5.0 mm | 500–700 RPM | 350–500 RPM | 900–1200 RPM | 1100–1500 RPM |
| #7 (1/4") / DIN 333 6.3 mm | 400–550 RPM | 275–400 RPM | 700–950 RPM | 900–1200 RPM |
| #8 (5/16") / DIN 333 8.0 mm | 325–450 RPM | 225–325 RPM | 550–750 RPM | 700–950 RPM |
Starting values for HSS centre drills running with adequate cutting fluid. Reduce by 25% if the workpiece is cast or work-hardened. For carbide centre drills (Sutton D318/D319), increase HSS values by 2–3× provided the spindle has minimal runout and the workpiece is rigidly held.
For deeper coverage of lathe spindle RPM calculation, surface speed formulas, and CSS vs G97 selection, see our Lathe RPM Formula Guide. For drill-bit speeds across the full range of hole-making operations, see the Cutting Speeds and Feeds Chart.
Why centre drills break — and how to prevent it
Centre drills have a higher breakage rate than any other drill or cutter in the workshop. The cause is always the same root issue: the small pilot tip is the weakest part of the tool, and breaking it ruins the whole drill (the body alone has no value).
| Cause | Why it happens | Prevention |
|---|---|---|
| Insufficient cutting fluid | The pilot tip is small and runs hot; without lubrication it work-hardens the material it contacts and stalls | Apply cutting oil, coolant or kerosene generously. Re-apply every few seconds during cutting. The Practical Machinist consensus: "fastest way to break a centre drill is to use it dry." |
| Spindle/chuck runout | Even 0.05 mm of runout causes the pilot to wobble, hammer the workpiece on each revolution, and snap on impact | Use an ER collet rather than a Jacobs chuck. Indicate the chuck if precision work. Replace worn chucks. |
| Hardened or surface-hardened material | HSS pilot tip cannot cut hardened steel — it skids, then breaks under feed pressure | Switch to solid carbide centre drill (Sutton D318 or D319) for surface-hardened workpieces; soften the surface with a spot drill or grinding first |
| Excessive feed pressure | The pilot tip rated for steady cut at 0.05–0.10 mm/rev breaks if pushed at 0.3 mm/rev | Use a controlled feed — tailstock handwheel with steady rotation, not impatient hand pressure |
| Drilling too deep — body engages | Once the body shoulder is fully engaged, the cutting forces increase rapidly and the pilot can't take the load | Stop at half to two-thirds shoulder engagement. Use the body shoulder mark on the drill to gauge depth. |
| Workpiece end not faced | An irregular cast or sawn end deflects the centre drill on the first revolution; pilot snaps | Face the end first. Always. |
| Wrong RPM for size | Running a #2 centre drill at 3500 RPM (suited for a #1) burns the pilot or breaks it on contact | Match RPM to size — see speeds table above |
Recovering from a broken pilot tip: the broken tip is usually small enough to dig out with a sharp scriber or ground tool. For a centre drill broken in a precision shaft end, a boring tool can be used to bore around the broken tip — when the bore reaches just past the broken section, the tip falls free. For a small broken tip in a finished workpiece face that must be preserved, the part is often scrapped — there is no clean recovery without damaging the surrounding face.
Centre drill vs combined drill-and-countersink
"Combined drill and countersink" is the formal full name for a centre drill — it describes the dual function of the tool: it drills the small pilot AND countersinks the 60° (or 90°) face in a single operation. In Australian usage, "centre drill" is the everyday term while "combined drill and countersink" is the formal catalogue term. AIMS Industrial's collection is named accordingly: the /collections/combined-drill-countersinks URL.
Some specialist tools labelled "combined drill and countersink" are NOT centre drills in the lathe sense — they are larger drill bits with a 60° or 82° countersink upper section, used for drilling and countersinking machine screw clearance holes in a single operation. These produce a clearance hole + countersink, not a 60° lathe centre. Confirm what you need:
| Tool | Pilot Ø | Body Ø | Countersink angle | Use |
|---|---|---|---|---|
| Centre drill (DIN 333 / ANSI B94-11) | 1.0–10.0 mm | 3.15–25 mm | 60° (matches lathe centre) | Lathe tailstock support hole |
| Combined drill-and-countersink for fasteners (90° type) | 3 mm – 12 mm (matches screw clearance) | 6–25 mm (matches screw head) | 90° (matches metric ISO countersunk screw head) | Drilling + countersinking M3 to M12 countersunk machine screw clearance holes in one pass |
| Combined drill-and-countersink for fasteners (82° type) | 3/16" – 1/2" (matches screw clearance) | 1/4"–1" (matches screw head) | 82° (matches imperial UNC/UNF countersunk screw head) | Drilling + countersinking imperial countersunk screws |
If you need to install a countersunk fastener, you want the 90° (metric) or 82° (imperial) combined drill — see our Counterbore and Countersink Reference for full coverage of fastener-mounting hole types. If you need to mount a workpiece between lathe centres, you want a centre drill (DIN 333 or ANSI B94-11).
AIMS Industrial centre drill range
AIMS stocks a comprehensive centre drill range covering both standards (DIN 333 metric, ANSI B94-11 imperial) and four cutting tool grades (HSS, cobalt, solid carbide, indexable). The full centre drill collection is at /collections/combined-drill-countersinks.
| Product | Standard | Material | Use |
|---|---|---|---|
| Sutton Tools D135 | DIN 333 form A | HSS | Standard metric centre drilling. Sizes from 1.6 mm. Australian-made. |
| Sutton Tools D136 | ANSI B94-11 plain type | HSS | Imperial standard. Sizes #1 through #8 individually. Sutton D136 7/32" #6 covers most general-purpose imperial work. |
| Sutton D136SCD1 | ANSI B94-11 plain type | HSS | 5-piece set #1 through #5 — the standard workshop set covering shaft work between approximately 6 mm and 50 mm diameter. |
| Sutton D318 | ANSI B94-11 plain type | Solid carbide bright (VHM) | Hardened steel and surface-hardened materials. Sizes from 3/64". |
| Sutton D319 | ANSI B94-11 plain type | Solid carbide TiCN-coated (VHM TiCN) | Production runs in abrasive cast iron and surface-hardened steel — TiCN coating extends life 25–40% over uncoated carbide. |
| Bordo HSS Centre Drill Bit | ANSI B94-11 | HSS | Individual sizes — general-purpose alternative to Sutton at competitive pricing. |
| Bordo HSS Centre Drill Set, 5 Pieces | ANSI B94-11 | HSS | 5-piece set #1–#5 — value-tier alternative to Sutton D136SCD1. |
| SECO Minimaster T60M (90° SIG) | Indexable carbide insert | Carbide insert with steel body | CNC production centre drilling — 90° tip variant. |
| SECO Minimaster T60M (120° SIG) | Indexable carbide insert | Carbide insert with steel body | CNC production centre drilling — 120° tip variant. |
For most Australian workshop work, Sutton D135 (DIN 333) or D136 (ANSI B94-11) HSS in a 5-piece set covers everything. Step up to D318 / D319 carbide for hardened or surface-hardened workpieces. Step up to SECO indexable for CNC production runs in the hundreds or thousands.
For application-specific advice, hard-to-find sizes, or matching a centre drill to existing equipment, call our team on (02) 9773 0122 or contact AIMS Industrial. Our team includes engineering specialists who handle lathe and machining tool selection daily.
Centre drill selection checklist
- Standard — DIN 333 for metric drawings; ANSI B94-11 for imperial drawings or Sutton stock equivalents.
- Form (DIN 333 only) — A for general use; B for protected centres on precision shafts; R for ground/hardened centres.
- Size — match pilot diameter to required centre hole. For shaft work, pilot diameter typically 8–15% of shaft diameter.
- Material — HSS for general; cobalt (HSS-E) for stainless; solid carbide for hardened or surface-hardened workpieces; TiCN-coated carbide for abrasive materials and production runs.
- Set vs individual — 5-piece set (#1–#5 ANSI or 1.6–4.0 mm DIN) covers most workshop needs; individual sizes for specific replacement.
- Cutting fluid — non-negotiable. General cutting oil for steel, soluble coolant for stainless, kerosene for aluminium.
- Holder — ER collet for precision (lower runout); Jacobs chuck for general work.
- Speed — match RPM to size and material per the speeds table above.
- Depth — half to two-thirds shoulder engagement for lathe work; just past surface break for mill / drill press location.
Frequently Asked Questions
Quick reference answers to the most common questions on centre drills, sizes, lathe vs CNC use, breakage prevention and Australian workshop practice.
What is a centre drill bit?
A centre drill bit is a stepped two-diameter cutting tool that produces a 60° conical hole used to support a workpiece between lathe centres. It has a small pilot tip (the cutting end) extending from a 60° shouldered body. The pilot creates a small clearance hole at the bottom of the centre, and the 60° shoulder creates the bearing surface that the lathe live or dead centre rests in. Centre drills are governed by DIN 333 (metric, with forms A, B and R) and ANSI B94-11 (imperial, sized #00 through #8).
What is the difference between a centre drill and a spot drill?
A centre drill produces a 60° conical hole for lathe tailstock support — its primary purpose. It has a small pilot tip below a 60° shoulder. A spot drill creates a precise location indent for a follow-up twist drill on a milling machine or CNC. It has no pilot — just a single point at the matching angle of the follow-up drill (90°, 118° or 140°). Use a centre drill for lathe work; use a spot drill for CNC drill location starts. The centre drill on CNC works but is suboptimal because its small pilot tip cannot run at the correct surface speed for the body.
Is a centre drill the same as a self-centering drill bit?
No — they are completely different tools. A centre drill (DIN 333 or ANSI B94-11) is an engineering and machining tool that produces a 60° conical hole for lathe tailstock support. A self-centering drill bit (sometimes called a Vix bit or hinge bit) is a woodworking tool used to drill a centred pilot hole through a hinge, bracket or fitting jig — it has a spring-loaded outer sleeve that centres on the screw clearance hole and an inner drill bit that follows. They are not interchangeable. If you need to mount a shaft between lathe centres, you want a centre drill. If you need to fit a hinge to a cabinet, you want a self-centering drill bit.
What does DIN 333 specify?
DIN 333 is the German (and now international) standard for centre drill bit geometry — the metric standard. It defines three forms: DIN 333-A (60° pilot + 60° countersink only — the standard general-purpose form), DIN 333-B (adds a 120° outer protective chamfer to shield the centre hole during subsequent operations), and DIN 333-R (curved radius profile instead of conical — used on hardened or surface-ground centre holes). The matching standard for the centre HOLE in the workpiece is DIN 332-1. ISO 866 covers the carbide variant.
What size centre drill should I use?
Centre drills are sized by pilot diameter (DIN 333) or by ANSI number (#1 through #8). For shaft work, the pilot diameter is typically 8–15% of the shaft diameter. A 25 mm shaft takes a #2 or #3 centre drill (5/64" or 7/64" pilot — about 2 mm or 2.8 mm). A 50 mm shaft takes a #5 (3/16" pilot — about 4.8 mm). For drill press / mill location pilot work, the smallest centre drill that produces a clean indent is sufficient — a #1 or #2 covers most location-pilot work.
How deep should I drill with a centre drill?
For lathe tailstock support, drill until the 60° shoulder is half to two-thirds engaged in the workpiece — this produces a countersink with sufficient bearing surface for the live or dead centre. The standard rule of thumb: countersink diameter should be 60–80% of shaft diameter for medium-duty work, scaling up to 100% for heavy cuts on long shafts. For drill press or mill location-pilot work, drill only until the pilot tip just breaks the surface (1–2 mm depth) — the follow-up twist drill needs only an indent to locate, not a full countersink.
Do centre drills come in metric and imperial?
Yes — both standards are used in Australian workshops. DIN 333 (metric) sizes are designated by pilot diameter in millimetres: 1.0, 1.25, 1.6, 2.0, 2.5, 3.15, 4.0, 5.0, 6.3, 8.0, 10.0 mm. ANSI B94-11 (imperial) sizes are designated by number: #00 (smallest), #0, #1 through #8 (largest). Sutton Tools manufactures both metric (D135 series, DIN 333) and imperial (D136 series, ANSI B94-11) ranges in Australia. AIMS Industrial stocks both — the choice depends on whether the drawing specifies metric or imperial.
What angle is a centre drill?
Standard centre drills have a 60° angle on the countersink shoulder — this matches the 60° angle of standard live and dead centres used in lathe tailstocks. The 60° angle is universal across DIN 333, ANSI B94-11, ISO 866 and JIS standards for general lathe work. Some specialty centre drills are made in 75° or 90° angles for specific applications (heavy industrial lathes with non-standard tailstock centres), but these are uncommon. If you're not sure which angle, the 60° is correct for any standard lathe.
Why does my centre drill keep breaking?
The small pilot tip is the weakest part of the tool and the most common failure point. The top causes (in order of frequency): (1) insufficient cutting fluid — the pilot runs hot and snaps. Apply cutting oil generously. (2) Spindle or chuck runout — even small runout makes the pilot hammer on each revolution. Use an ER collet rather than a Jacobs chuck. (3) Hardened or surface-hardened material — HSS pilots cannot cut hardened steel; switch to solid carbide (Sutton D318 or D319). (4) Excessive feed pressure — controlled feed via tailstock handwheel rather than aggressive hand pressure. (5) Drilling too deep — stop at half to two-thirds shoulder engagement. (6) Wrong RPM for the size.
Can I use a centre drill in a drill press?
Yes — a centre drill in a drill press is the standard low-cost setup for general workshop pilot drilling. The drill press provides better alignment than hand-drilling, the centre drill's stiff body resists the deflection that a normal twist drill would suffer, and the pilot tip produces a precise indent for the follow-up twist drill. Match the drill press RPM to the centre drill size and material — typically the lowest pulley setting on a benchtop drill press is correct for a #2 or #3 centre drill in steel. Apply cutting oil generously.
What is a combined drill and countersink?
"Combined drill and countersink" is the formal catalogue name for a centre drill — it describes the dual function of the tool: it drills a small pilot AND countersinks the 60° (or 90°) shoulder in a single operation. In Australian usage, "centre drill" is the everyday term while "combined drill and countersink" is the formal name. AIMS Industrial's centre drill collection is named accordingly. Note that some specialty 90° or 82° tools labelled "combined drill and countersink" are designed for fastener clearance holes (countersinking machine screw heads), not for lathe centres — confirm the angle and intended use before ordering.
What speed should I run a centre drill?
Centre drill RPM scales with size — smaller drills run faster, larger drills run slower. Typical starting speeds in mild steel HSS: #1 (1500–2000 RPM), #2 (1200–1500 RPM), #3 (1000–1300 RPM), #4 (800–1100 RPM), #5 (600–800 RPM), #6 (500–700 RPM). Reduce by 25% for stainless steel; increase by 50% for aluminium and brass. Carbide centre drills (Sutton D318/D319) can run 2–3× HSS speeds provided the spindle has minimal runout and the workpiece is rigidly held. Apply cutting fluid generously regardless of speed — running dry is the fastest way to break a centre drill.
What does the # number on a centre drill mean?
The # number is the ANSI B94-11 imperial size designation. Each number corresponds to a specific pilot diameter and body diameter combination. #00 (smallest, 1/32" pilot), #0 (1/32" pilot, slightly longer than #00), #1 (3/64" pilot), #2 (5/64" pilot), #3 (7/64" pilot), #4 (1/8" pilot), #5 (3/16" pilot), #6 (7/32" pilot), #7 (1/4" pilot), #8 (5/16" pilot — largest standard size). The standard 5-piece workshop set covers #1 through #5 — the range that handles most general lathe and pilot drilling work.
Should I centre drill before drilling?
On a lathe, yes — always. The centre drill creates the supporting centre that the tailstock relies on for the entire turning operation. On a drill press or mill, centre drilling before twist drilling is good practice for precision work where location accuracy matters — the centre drill's stiff body resists deflection that would let a twist drill walk. For modern CNC machining with solid-carbide drills, the centre drill (or spot drill) step can sometimes be skipped — modern self-centering carbide drill geometries locate accurately on first contact. On manual machining or general workshop work, the centre drill / spot drill step adds precision at minimal time cost.
What is a centre drill made of?
Three main material grades. HSS (M2 or M7 high-speed steel) is the default — tough, resharpenable, low cost; suits general lathe and drill press work in steel, brass, aluminium and cast iron. HSS-E or M35 cobalt has higher heat resistance and longer tool life — used for stainless steel, abrasive cast iron and low-volume production runs. Solid carbide (VHM) — typically with a TiCN coating for extended life — cuts hardened or surface-hardened material (Rc 45+) but is brittle and breaks instantly under shock load. For most Australian workshop use, HSS covers 90% of work. Step up to cobalt for stainless, solid carbide for hardened material.