NC Spotting Drill Guide: 90° vs 120° vs 142° Point Angles, DIN 1897, VHM Carbide & CNC Selection
NC spotting drills create precise centring spots that prevent twist drill wander on CNC machining centres. They are the first tool in the drilling sequence for every accurate hole on a CNC mill — a 0.5mm wander from a drill without a spot becomes a positional tolerance failure on the inspection report. This guide covers the 90° vs 120° vs 142° point angle selection rule (the universal "matching the following drill's point" principle), DIN 1897 vs DIN 333 (the spotting drill vs centre drill disambiguation), HSS cobalt vs VHM solid carbide with AlCrN coating, CNC speed and feed by material, and the AIMS Sutton + Bordo range — grounded in 18+ forum-validated insights from Practical Machinist, Hobby-Machinist, Home Shop Machinist BBS and CNCCookbook.
AIMS stocks 10 NC spotting drill products. Sutton Tools dominates 9:1 with the deepest range of any product in our Sutton brand series — from cobalt HSS TiN workshop tier (D175 90°, D176 120°, plus 4-piece and 5-piece sets) through to VHM solid carbide premium CNC tier (D355 90°, D364 90° AlCrN, D365 142°, D365 142° AlCrN). See the Spotting Drill Bits & Sets collection.
What is an NC spotting drill — and why every CNC job starts with one
An NC spotting drill (also called a spot drill or NC spot drill) is a short, rigid drill bit designed to create a small conical depression at the precise location where a follow-up drill bit will enter the workpiece. The "NC" prefix indicates the tool is intended for Numerical Control (CNC) machining centres rather than manual lathe centre work.
The reason every accurate CNC drilling job starts with a spotting drill: standard twist drills wander when they first contact a workpiece. The drill point cannot resist sideways force well, so the bit drifts in the direction of any flat, hard spot or surface imperfection — 0.2 to 0.5mm of wander on a 6mm drill is typical. On a positional tolerance of ±0.1mm, that's a fail. The spotting drill creates a centred conical pocket the following drill seats into, fixing the hole location before the wandering force can act.
Spotting drills are short — typically 30–60mm overall length — which makes them rigid. The short flute length combined with the larger shank diameter gives them resistance to deflection that a long jobber drill simply cannot match. They cut only 1–3mm deep into the workpiece — just enough to create a registration cone, not a hole.
Spotting drill vs centre drill — the DIN 1897 vs DIN 333 disambiguation
The most-asked question in CNC machining tooling: what's the difference between a spotting drill and a centre drill? They look similar at a glance, but they are different tools for different jobs.
| Property | NC Spotting Drill (DIN 1897) | Centre Drill (DIN 333) |
|---|---|---|
| Designed for | CNC machining centres, hole-start centring before drilling | Lathe tailstock support, creating a 60° centre in workpiece end face |
| Geometry | Single conical point — 90°, 120° or 142° included angle | Combined drill-and-countersink — small pilot point + 60° countersink shoulder |
| Cutting depth | 1-3mm shallow centring spot | Deep enough to seat a lathe centre (typically 3-15mm) |
| Standard | DIN 1897 | DIN 333 (Form A, B, R) / ANSI B94-11 |
| Length | Short and rigid (30-60mm typical) | Short but with characteristic stepped pilot geometry |
| Use case | Production CNC drilling — start every hole with a spot | Lathe work — support workpiece between centres |
| Typical material | 5% or 8% cobalt HSS, or solid carbide (VHM) | HSS or cobalt HSS — carbide rare for centre drills |
Workshop reality: many shops use centre drills as spotting drills. It works, but it's a compromise. Centre drills are designed for a different geometry (the 60° countersink follows a small pilot drill), and using one as a spot drill gives a less-clean centring cone than a purpose-built spotting drill. The follow-up twist drill can chatter on entry. The Practical Machinist consensus: if you're doing volume CNC work, buy proper NC spotting drills. If you have one centre drill on hand for the occasional spot, it'll do.
For deep coverage of centre drills specifically — including the BS 328 / DIN 333 standards, lathe centre drilling technique, and the centre-drill vs combined-drill-countersink distinction — see our Centre Drill Bit Guide.
The point angle decision — 90° vs 120° vs 142°
Point angle is the most consequential decision when selecting an NC spotting drill. The choice depends on the drill bit that will follow the spot.
| Spotting drill angle | Best for | Why this angle | Sutton SKU |
|---|---|---|---|
| 90° | Twin-purpose spotting and chamfering. Also for follow-up drills with <115° points | Creates a 90° chamfer at hole entry. Two jobs in one tool — spotting + chamfering | Sutton D175 90° HSS Cobalt TiN · Sutton D355 90° VHM · Sutton D364 90° VHM AlCrN |
| 120° | Production CNC default — when follow-up drill is standard 118° point | Sits 2° wider than 118° drill — drill centre contacts spot bottom first, no chatter | Sutton D176 120° HSS Cobalt TiN |
| 142° | For follow-up drills with 135-140° points (some imported and carbide drills) | Sits 2-7° wider than 135-140° drill — same drill-centre-first principle | Sutton D365 142° VHM · Sutton D365 142° VHM AlCrN |
The "118° drill = 120° spotting drill" rule
The universal CNC convention: the spotting drill must have a LARGER included angle than the drill that follows. This sounds counter-intuitive, but the geometry is unambiguous.
When a follow-up drill enters the spot, the drill's point must contact the bottom of the spot first — at the centre. If the spotting drill has a smaller (more pointed) angle than the follow-up drill, the drill's cutting lips contact the spot wall before the drill point reaches the spot bottom. The result is chatter, drill walk, and a sub-centred hole.
By making the spot wider than the drill, the drill point reaches the centre of the spot before the cutting lips touch the wall. The drill seats cleanly, cuts true to centre, and the resulting hole is on-position.
| Follow-up drill point angle | Correct spotting drill angle | Typical drill type |
|---|---|---|
| 118° | 120° | Standard HSS jobber drill, most workshop drill bits |
| 135° | 140° or 142° | Split-point HSS or cobalt drill, carbide drill |
| 140° | 142° | Some imported carbide drills |
| Under 115° | 90° | Soft-material drills (timber, plastic) — also gives chamfer bonus |
Forum-validated practitioner direct quote from Practical Machinist: "Using 120 for a 118 drill gives less drill wear and more tool life with the drill that follows it, with less chatter at the entrance and better finish." The 2° margin is the workshop standard.
The 90° exception — when chamfering matters. 90° spotting drills are used when the same operation should also chamfer the hole entrance (e.g. for tap entry, deburring, or socket-head cap screw seat). The 90° point creates a 45° chamfer at the hole edge. The trade-off is potential chatter when the follow-up drill enters (the 118° drill cutting lips can contact the 90° wall before the drill point reaches the centre). For production volume, 120° is preferred — for occasional work where chamfering saves an operation, 90° wins.
HSS Cobalt vs VHM Solid Carbide — the cost vs performance decision
Sutton's NC spotting drill range splits into two material families: cobalt HSS for the workshop tier, and VHM (Vollhartmetall — solid tungsten carbide) for the premium CNC tier.
| Property | HSS Cobalt (5% or 8%) | VHM Solid Carbide |
|---|---|---|
| Best for | Workshop CNC, mixed-material work, manual mills, hobby machining | Production CNC, high-volume runs, hardened steel and stainless |
| Cost | 1x (baseline) | 3-5x baseline |
| Cutting speed | Standard — runs at HSS feeds and speeds | 2-3x HSS speed capability |
| Heat tolerance | Softens above ~600°C | Stable to ~1000°C+ |
| Brittleness | Tolerant of imperfect setups, minor vibration | Brittle — chips on chatter, side-load, or workpiece movement |
| Manual mill use | Suits manual machining | Risk of chipping — needs rigid CNC setup |
| Re-sharpenable | Yes (specialist service) | No — consumed |
| Sutton SKUs | D175 90°, D176 120° + 4pc and 5pc sets | D355 90°, D364 90° AlCrN, D365 142°, D365 142° AlCrN |
The decision rule: for production CNC running mostly steel and stainless at standard feeds and speeds, VHM solid carbide is the right choice — the 3-5x cost is paid back through 2-3x cycle time reduction and longer tool life on demanding materials. For workshop CNC, manual mills, mould toolmaking and hobby machining, cobalt HSS is the practical pick — cheaper to replace when the geometry inevitably gets damaged, and tolerant of imperfect setups.
Forum-validated practitioner reality from Hobby-Machinist: "Carbide spot drills are brittle on manual mills — they chip with the slightest chatter or workpiece movement. Cobalt HSS is the practical choice for non-CNC work." VHM brittleness is a real constraint, not a marketing point.
Coatings — TiN vs AlCrN
Sutton's spotting drill coatings split into two tiers: TiN (titanium nitride, gold finish) on the cobalt HSS series, and AlCrN (aluminium chromium nitride, dark grey/blue finish) on the premium VHM carbide series.
- TiN (titanium nitride) — entry premium coating. Increases surface hardness to ~2300 HV (vs ~700-900 HV uncoated HSS). Friction coefficient reduced. Standard for cobalt HSS spotting drills. Best for mild steel, free-machining steels, brass, aluminium.
- AlCrN (aluminium chromium nitride) — premium coating, optimised for elevated temperatures. Surface hardness ~3200 HV. Resists thermal degradation above 800°C — suits dry high-speed CNC cutting where thermal generation is a problem. Standard for the Sutton D364 and D365 AlCrN variants. Best for stainless steel, titanium, hardened steel, and dry-cut CNC.
The choice between coated and uncoated, TiN and AlCrN, follows the production volume and material profile. Occasional shop use: uncoated or TiN. Daily CNC production in mixed materials: AlCrN. Stainless / hardened / dry cutting: AlCrN mandatory.
Sizing for CNC work — diameter and depth
NC spotting drills are available from approximately 3mm diameter up to 16mm. The diameter selection rule is straightforward: the spotting drill diameter should be slightly larger than the smallest hole diameter on the workpiece. A common production approach is to use a single spotting drill diameter (5mm, 6mm or 8mm depending on workshop standard) for all holes on a given component.
| Spotting drill diameter | Best for | Typical AIMS Sutton SKU coverage |
|---|---|---|
| 3-5mm | Small precision parts, electronics enclosures, mould components | Within D175 / D176 ranges, smaller sets |
| 6mm | Workshop CNC default — covers most general parts | D175, D176, D355, D365 single bits |
| 8mm | Production CNC default — covers most heavier parts | D175, D176, D355, D364, D365 single bits |
| 10-12mm | Larger parts, heavy structural components | D175, D176 larger sizes; D365 142° for matching carbide jobber drills |
Spotting depth. The forum-validated workshop default is 1/16" (1.6mm) for most production CNC. Some programmers reduce to 0.005" (0.13mm) — fingernail depth — for verification spots that confirm hole locations before the full job runs. Practical Machinist consensus: spot deeper than the chisel edge of the follow-up drill (typically 0.5-1mm) to ensure the drill point lands cleanly in the spotted cone.
Set vs individual selection. Mixed-work shops typically buy the Sutton D1750004 90° 4-piece set, D175SDT5 90° 5-piece set, or D1760004 120° 4-piece set for one-stop coverage across diameters. Production shops with a single dominant diameter buy individual D175 or D176 bits in volume for replacement.
Speed and feed — RPM by diameter, IPM by material
NC spotting drill speeds and feeds depend on cutter diameter, material, and the cutter substrate (HSS cobalt vs VHM carbide). The table below consolidates manufacturer data and forum-validated practitioner figures.
| Material | HSS cobalt SFM | VHM carbide SFM | Typical feed |
|---|---|---|---|
| Mild steel (1018, 1020) | 80-100 SFM | 250-400 SFM | 0.003-0.006 IPR |
| Stainless 304 / 316 | 30-50 SFM | 120-200 SFM | 0.002-0.004 IPR (slower) |
| Aluminium 6061 | 200-300 SFM | 500-800 SFM | 0.004-0.008 IPR |
| Brass / bronze | 150-250 SFM | 400-600 SFM | 0.003-0.006 IPR |
| Hardened steel (35-45 HRC) | Not recommended | 80-150 SFM | 0.001-0.003 IPR — VHM mandatory |
| Cast iron (grey) | 60-90 SFM | 250-350 SFM | 0.003-0.005 IPR — dry cut OK |
Practitioner reference figures. Forum-validated production speeds from Practical Machinist for general CNC spotting:
- 5/16" (8mm) VHM carbide spot drill in mild steel: 6,000 RPM at 5 IPM
- 5/16" VHM in stainless 304: drop to 4,000 RPM at 4 IPM with sulfur cutting oil
- 6mm HSS cobalt in mild steel: 2,000-3,000 RPM at 0.005 IPR feed
- Spotting depth: 0.062" (1.6mm) standard production default
For broader cutting speed reference across all machining operations, see our Cutting Speeds and Feeds Chart.
G82 dwell vs G81 — CNC programming for spot drills
The CNC programming convention for spot drilling: use G82 (drill with dwell) rather than G81 (standard drill cycle). The dwell holds the spotting drill at the bottom of the spot for a fraction of a second, allowing the cutting edges to remove any high spots in the cone and producing a perfectly uniform chamfer geometry.
Typical G82 dwell time for spot drilling: 0.1 to 0.5 seconds. The dwell:
- Ensures the spot reaches full programmed depth (chip evacuation completes)
- Produces a uniform chamfer around the hole edge (critical when the spotting drill doubles as a chamfer tool)
- Settles the spindle deflection — first-pass spots can be slightly off-centre from spindle dynamic deflection that the dwell allows to relax
The "0.005" verification spot" trick. Forum-validated CNC programmer practice from Practical Machinist: when verifying a new program before committing to the full job, reduce the spotting depth to 0.005" (0.13mm) — fingernail depth. This creates a visible witness mark at every hole location. The operator can inspect the spotted workpiece against the drawing before committing to deeper spotting and drilling. Saves a damaged part if the program has a hole position error.
The "do we still need pilot drills?" question
Pilot holes — drilling a smaller diameter hole first before the final drill — used to be standard practice for any drill above ~6mm in steel. Modern split-point drills (especially in cobalt and carbide) have largely eliminated this need for everyday CNC work.
Practical Machinist consensus: "Any CNC machine should drive a split-point drill into aluminium, mild steel, and annealed higher-strength steels up to 7/8"-1" diameter without a pilot hole." Modern drill geometry handles its own centring.
Pilot holes are still justified in specific scenarios:
- Long inserted drills or spade drills without their own pilot — these have no self-centring point and benefit from a stub pilot
- Very deep holes (depth-to-diameter ratios > 5:1) where chip evacuation is the constraint
- Hand drilling without a spotting cycle — manual drill press work where wander is hard to prevent
- Very large diameters (above 25mm) where the cutting load is high and centring forces are critical
For routine CNC drilling on a machining centre: spotting drill plus the final drill is the standard sequence. No pilot. The spotting drill does the centring work the pilot drill used to do.
Materials — what each Sutton spotting drill is best for
The Sutton range maps to specific material categories. Picking the right substrate and coating for the workpiece material matters more than picking a brand.
| Workpiece material | Best Sutton SKU choice | Why |
|---|---|---|
| Mild steel (1018, 1020) | D175 90° / D176 120° HSS Cobalt TiN | Workshop tier — cost effective for general production, TiN coating sufficient |
| Stainless 304 / 316 | D364 90° VHM AlCrN / D365 142° VHM AlCrN | AlCrN coating handles stainless's heat generation and work-hardening tendency |
| Aluminium 6061 / 7075 | D175 90° HSS Cobalt TiN (uncoated also OK) | Aluminium is soft — VHM carbide overkill, HSS works at higher speeds |
| Brass / Bronze | D175 90° / D176 120° HSS Cobalt TiN | HSS sufficient — match angle to follow-up drill |
| Hardened steel (35-45 HRC) | D355 90° / D365 142° VHM (with AlCrN for production) | HSS will burn — VHM solid carbide mandatory |
| Cast iron | D175 / D176 HSS Cobalt TiN, or D355 VHM for production | Cast iron dust is abrasive — TiN or VHM extends life |
| Plastic / composite | D175 90° HSS Cobalt TiN, run dry | HSS is fine — slow speed, sharp edges critical |
Cutting fluid selection
Spotting drill operations are short — 0.5 to 1 second at depth on most cycles. This makes cutting fluid less critical than for through-drilling, but the right fluid still extends tool life significantly.
- Air blast — fastest, no fluid handling. Standard for production aluminium and free-machining brass work.
- Flood coolant (water-soluble emulsion) — CNC machining centre default. 5-10% emulsion in water. Standard for steel, stainless, alloy steels.
- Through-spindle coolant (TSC) — premium CNC option. Coolant delivered through the spindle and out the cutter centre. Suits production VHM carbide work.
- Sulfur-based cutting oil — specifically for stainless 304/316 and difficult-to-machine alloys. Forum-validated practitioner standard for stainless spotting.
- Mineral cutting oil (general) — for manual mills running cobalt HSS spotting drills without flood coolant.
Do not use water alone (flash-rusts the spot bottom on steel), WD-40 (burns off, not a cutting lubricant), or engine oil (viscosity wrong for high-RPM work). See our Cutting Fluids Guide for full workshop selection.
Manual mills vs CNC machining centres — the VHM brittleness reality
This is the single biggest setup-versus-tooling trap. VHM solid carbide spotting drills are designed for rigid, accurate CNC machining centres — they assume the spindle, fixture and workpiece are all moving in known controlled ways. Manual mills do not provide this.
What kills VHM on manual mills:
- Chatter — quill deflection, belt drive vibration, workpiece resonance. VHM chips before it cuts.
- Side load — drilling off-perpendicular, accidentally moving the table during the cycle. VHM has no flexibility.
- Workpiece movement — a Kurt vise can flex 0.05mm under heavy clamp; that's enough to shatter a 6mm VHM spot drill on entry.
- Variable feed rate — manual quill feed is not constant. VHM wants smooth steady feed.
The practical rule for manual mills: use cobalt HSS spotting drills. The Sutton D175 90°, Sutton D176 120° and the Bordo HSS Cobalt are all suited to manual mill use. They tolerate the imperfect setup that VHM cannot.
For hobby CNC routers and small benchtop CNCs — the same rule applies. Sub-3HP spindles, polymer bed flex, less-than-perfect way alignment all contribute to setup imperfection that brittles VHM. Start with cobalt HSS; upgrade to VHM only if you've verified your setup is rigid enough.
Common failure modes
| Failure mode | Cause | Prevention |
|---|---|---|
| Spotting drill chips on entry | VHM in non-rigid setup, workpiece moves on first contact | Use cobalt HSS for non-rigid setups; verify fixture rigidity before VHM use |
| Follow-up drill chatters when entering spot | Spotting drill angle smaller than drill angle (90° spot + 118° drill) | Match: 120° spot for 118° drill, 142° spot for 135-140° drill |
| Hole position off after drilling | Spot too shallow — drill point didn't reach centre of spot | Spot at least 0.5mm deeper than follow-up drill chisel edge |
| Spotting drill burns / blue tinge (HSS) | RPM too high, no coolant, prolonged dry cut | Stick to material-appropriate SFM table; ensure coolant or fluid flow |
| Spot bottom not centred | Spindle deflection, no G82 dwell | Add 0.1-0.5 sec G82 dwell; check spindle runout |
| VHM coating worn / dull | Cut count exceeded, material harder than rated | Replace; AlCrN-coated for stainless and hardened work |
| HSS edges deformed | Material harder than HSS (workpiece overheated, hard spot) | Switch to VHM; check for material certification |
| Programmer mis-set spot depth | Multi-hole job, all spots at wrong depth | Use 0.005" verification spot before committing to full job depth |
| Stainless work-hardens before next pass | Slow feed or dwell on stainless — work-hardens surface | Maintain continuous feed; never dwell on stainless |
| Spotting drill walks off centre | Surface imperfection at start point; flat/scale spot | Verify clean surface; consider light facing pass before spotting |
AU brand reality — Sutton 9:1 at AIMS, honest scope on imports
AIMS Industrial stocks the deepest Sutton Tools NC spotting drill range of any Sutton brand category we've covered — 9 SKUs across cobalt HSS TiN and VHM solid carbide tiers, with 90°, 120° and 142° point angles. The Sutton range is comprehensive enough to be a single-brand workshop solution for AU CNC machining centres.
Sutton Tools (AU patriot — 9 SKUs)
Cobalt HSS TiN — workshop tier (5 SKUs):
- Sutton D175 90° Spotting Drill Bit, DIN 1897, Cobalt Steel, TiN — the workshop 90° default. For follow-up drills with point angles under 115°, or when chamfering is wanted.
- Sutton D1750004 90° Spotting Drill 4-Piece Set, 5% Cobalt HSS, TiN — 90° set covering common diameters in a single carded pack.
- Sutton D175SDT5 90° Spotting Drill 5-Piece Set, 5% Cobalt HSS, TiN — extended 90° set, broader diameter coverage.
- Sutton D176 120° Spotting Drill Bit, DIN 1897, Cobalt Steel, TiN — the workshop 120° default. For 118° follow-up drills. The most common production CNC spotting angle.
- Sutton D1760004 120° Spotting Drill 4-Piece Set, 5% Cobalt HSS, TiN — 120° set for shops standardising on 118° drills.
VHM Solid Carbide — premium CNC tier (4 SKUs):
- Sutton D355 90° Carbide Spotting Drill Bit, VHM — solid carbide 90° for production CNC. Suitable for steel, stainless and harder materials.
- Sutton D364 90° Carbide Spotting Drill Bit, VHM, AlCrN coated — premium 90° with AlCrN coating. Best pick for production stainless and high-speed dry CNC work.
- Sutton D365 142° Carbide Spotting Drill Bit, VHM — solid carbide 142° for 135-140° follow-up drills.
- Sutton D365 142° Carbide Spot Drill, VHM, AlCrN coated — premium 142° with AlCrN. The top-tier pick for production CNC with carbide jobber drills.
Bordo (AU value — 1 SKU)
- Bordo HSS Cobalt TiAlN Coated Spotting Drill Bit — value-tier alternative to the Sutton D175/D176. TiAlN coating offers similar thermal performance to AlCrN at lower cost.
Honest scope — brands NOT stocked at AIMS
The international NC spotting drill market includes premium specialty brands AIMS does not currently stock:
- Sandvik Coromant (Sweden) — global production CNC specialty premium
- Iscar (Israel) — production CNC specialty
- Garr Tool, Harvey Performance, OSG (USA / Japan) — US/JP production CNC premium
- Walter, Gühring, Fraisa (Germany) — European production CNC specialty
- Niagara Cutter, Helical Solutions (USA) — US machining centre specialty
- Mitsubishi Materials (Japan) — JP production CNC premium
For these brands, we'll source through our supplier network — call AIMS on (02) 9773 0122 or use the contact form with your spec.
AU CNC manufacturing — where Sutton spotting drills earn their keep
The Australian CNC manufacturing sector is smaller than the US or European markets but technically demanding. Sutton Tools' Thomastown VIC manufacturing facility serves this sector directly, and the NC spotting drill range is one of Sutton's bread-and-butter product families for AU machine shops.
Sectors using Sutton NC spotting drills in production:
- Aerospace and defence — Marand (Melbourne), BAE Systems (Williamtown), ASC (Adelaide naval shipbuilding) — precision machining of aluminium and titanium components requiring tight positional tolerances. AlCrN-coated VHM is the standard tooling.
- Mining equipment — Bisalloy steel processing, WesTrac Caterpillar component remanufacture, Komatsu service centres. Heavy structural component drilling on CNC machining centres. D175 90° and D176 120° cobalt HSS dominant for general production.
- Agricultural and earthmoving machinery — chassis and implement manufacture, often in mild steel and HSLA grades. Cost-effective HSS cobalt range standard.
- Mould toolmaking — plastic injection mould and die-casting mould production. Precision spotting of cooling channels, ejector pin holes, vent holes. Mix of HSS and VHM depending on mould steel hardness.
- Precision component manufacture — instrumentation, medical devices, electronics enclosures. D175 90° + smaller diameter sets dominant.
- Repair and maintenance shops — manual mill work on Bridgeport-style machines, where VHM brittleness is a real constraint. Cobalt HSS the standard pick.
Sutton's competitive position: against Sandvik Coromant, Iscar, Garr, OSG and other international premium brands, Sutton competes on AU-manufactured origin, local technical support, and short supply chain. For Australian production shops doing volume work, Sutton's D175/D176 HSS cobalt range is the workshop-cost standard, and the D355/D364/D365 VHM range is the premium production tier — both available off-the-shelf at AIMS rather than imported lead-time.
NC spotting drill selection checklist + common mistakes
Before buying, run through this 8-point checklist:
- Identify the follow-up drill angle. Standard 118° HSS = 120° spot. Split-point 135° = 140° or 142° spot. Match the angle.
- Decide HSS Cobalt or VHM Carbide. Workshop/manual mill = HSS cobalt. Production CNC = VHM. Hardened steel/stainless production = VHM AlCrN.
- Pick the coating. Mild steel/aluminium/brass = TiN. Stainless/hardened/dry CNC = AlCrN. Both are sufficient for general workshop use.
- Diameter. Workshop default 5-6mm for general parts; 8mm for heavier work. Match to your smallest production hole.
- Set vs single. Mixed work = 4 or 5-piece set. Production with one dominant diameter = singles in volume.
- CNC programming. Use G82 dwell, not G81. Spot depth 1.6mm (1/16") standard, 0.13mm (0.005") for verification.
- Cutting fluid. Match to material. Stainless = sulfur cutting oil. Steel = water-based emulsion. Aluminium = air blast OK.
- Backup plan. Stock at least one matching pilot HSS bit in case the VHM tip chips mid-job.
Top 10 forum-validated mistakes:
- Using a centre drill as a spot drill — works but compromises quality. Buy the right tool.
- Wrong point angle — 90° spot with 118° drill gives chatter. Match the geometry.
- VHM carbide on a manual mill — chips at the first vibration. Use cobalt HSS.
- Spot too shallow — drill doesn't seat in cone. Spot at least chisel-depth + 0.5mm.
- Spot too deep — wastes cycle time, no benefit beyond 1/16" for production. Standard is 0.062".
- G81 instead of G82 — no dwell means non-uniform chamfer. Use G82 with 0.1-0.5 sec dwell.
- Spotting in stainless without sulfur oil — work-hardens before next pass. Use sulfur-based cutting fluid.
- HSS in hardened steel — burns the cutting edges in seconds. Use VHM.
- Pilot drill plus spotting drill plus final drill — redundant for diameters under 7/8". Spot + drill only.
- Trying to chamfer with a 120° spot drill — produces non-standard 60° chamfer. Use 90° if chamfering required.
Frequently Asked Questions
What is an NC spotting drill used for?
An NC spotting drill creates a small conical depression at the precise location where a follow-up drill bit will enter a workpiece on a CNC machining centre. The spot prevents twist drill wander — without it, a standard drill can drift 0.2-0.5mm from the intended hole location, which fails most positional tolerance specs. Every accurate CNC drilling job starts with a spotting drill.
What is the difference between a spotting drill and a centre drill?
A spotting drill (DIN 1897) is a single-conical-point tool used on CNC machining centres to create a centring spot for a following drill. A centre drill (DIN 333) is a combined drill-and-countersink used on lathes to create a 60° centre in the workpiece end face for tailstock support. Spotting drills come in 90°, 120° and 142° point angles to match follow-up drills; centre drills have a fixed 60° countersink for lathe centre fit. See our Centre Drill Bit Guide for the centre-drill deep-dive.
Which point angle should I buy — 90, 120 or 142 degrees?
Match the spotting drill angle to the follow-up drill point angle, with the spotting drill 2-7 degrees wider. Standard 118° HSS jobber drill = 120° spotting drill (Sutton D176). Split-point 135° cobalt or carbide drill = 140° or 142° spotting drill (Sutton D365). For occasional work or when chamfering is also wanted, 90° (Sutton D175 or D355) serves both jobs — spotting plus 45° chamfer at hole entry.
Why does my drill chatter after spotting?
Almost always because the spotting drill angle is smaller (more pointed) than the follow-up drill angle. A 90° spotting drill creates a 45° cone wall; a 118° drill's cutting lips contact the cone wall before the drill point reaches the centre, causing chatter. Fix: use a 120° spotting drill with a 118° follow-up drill. The spot needs to be wider than the drill.
HSS Cobalt or VHM Carbide — which should I buy?
VHM Solid Carbide for production CNC machining centres running mostly steel and stainless at standard or high feeds and speeds, where the 3-5x cost is paid back through 2-3x cycle time reduction and longer tool life. HSS Cobalt for workshop CNC, manual mills, mould toolmaking and hobby machining where setup rigidity is imperfect and VHM brittleness becomes a problem. Workshop reality: VHM chips on chatter, cobalt HSS tolerates it.
What is DIN 1897?
DIN 1897 is the German industrial standard for NC spotting drills — short, rigid drills with single conical points for CNC hole-start centring. It defines the diameter sizes, overall length, shank type and tolerance class. Sutton D175 and D176 are DIN 1897 compliant. The standard differs from DIN 333 (centre drills for lathe work) — two different products for two different jobs.
What does VHM mean?
VHM is the German abbreviation for "Vollhartmetall" — literally "full hard metal" — meaning solid tungsten carbide. The opposite is carbide-tipped (HSS body with carbide tips brazed on the cutting edges). VHM is more rigid, holds an edge longer, and tolerates higher cutting speeds than HSS or carbide-tipped tools, but is brittle and chips on impact or vibration. Sutton's D355, D364 and D365 are VHM. Sutton's D175 and D176 are HSS cobalt — not VHM.
What does AlCrN coating do?
AlCrN (aluminium chromium nitride) is a premium thin-film coating applied to cutting tools — particularly VHM carbide. It increases surface hardness to ~3200 HV and resists thermal degradation above 800°C. The coating is dark grey to blue in colour. Best for stainless steel, hardened steel and dry high-speed CNC cutting where thermal generation is a constraint. Sutton's D364 90° AlCrN and D365 142° AlCrN variants are the premium picks for production stainless work.
Do I need a pilot drill before spotting?
No. The whole point of using a spotting drill is to eliminate the need for a pilot. Modern split-point twist drills (HSS, cobalt or carbide) handle their own centring on diameters up to 7/8"-1" in steel and aluminium when started in a properly spotted hole. Pilot drills are only justified for very large diameters (above 25mm), very deep holes (depth-to-diameter > 5:1), or specialty long-inserted/spade drills without self-centring geometry.
Should I use G82 dwell when spot drilling?
Yes. G82 (drill with dwell) is the CNC programming standard for spot drilling. The dwell — typically 0.1 to 0.5 seconds at depth — ensures the spot reaches programmed depth, produces a uniform chamfer around the hole edge, and allows spindle deflection to settle for a centred cone bottom. G81 (standard drill cycle) without dwell can produce off-centre or non-uniform spots.
How deep should I spot drill?
The standard production CNC default is 0.062" (1.6mm or 1/16") deep. This is enough to create a registration cone for the follow-up drill while minimising cycle time. For verification spots (confirming hole locations before committing to the full job), reduce to 0.005" (0.13mm) — fingernail depth — which creates a visible witness mark without removing meaningful material. Spot at least chisel-depth + 0.5mm of the follow-up drill, ensuring the drill point lands inside the cone.
What RPM and feed should I run a spot drill at?
For a 5/16" (8mm) VHM carbide spot drill in mild steel: 6,000 RPM at 5 IPM (forum-validated CNC default). For 6mm HSS cobalt in mild steel: 2,000-3,000 RPM at 0.005 IPR. Stainless 304 needs to drop to 4,000 RPM or slower with sulfur cutting oil. Always use the SFM tables (80-100 SFM for HSS cobalt in mild steel; 250-400 SFM for VHM carbide) and apply your spindle's RPM equation.
Can VHM carbide spot drills be used on a manual mill?
Risky. VHM solid carbide is brittle — it chips with chatter, side load or workpiece movement. Manual mills (Bridgeport-style) introduce all three: quill deflection, manual feed inconsistency, and vise flex. Cobalt HSS is the practical pick for manual machining. Save VHM for rigid CNC machining centres. The Sutton D175 90° and D176 120° HSS cobalt range is the AU manual mill default.
Why is Sutton not using DIN 1897 on the VHM range?
DIN 1897 specifies cobalt HSS substrate. The Sutton D355, D364 and D365 are VHM solid carbide — outside DIN 1897 scope but still designed for the same NC spotting drill function. Sutton uses Sutton's own internal geometry specification for the carbide range, with the same 90° / 120° / 142° point angle options as the DIN 1897 HSS range. Functionally equivalent for the user — just different substrate and standard reference.
Where do I buy NC spotting drills in Australia?
AIMS Industrial stocks 10 NC spotting drill products — 9 Sutton Tools (D175 90°, D176 120°, D355 90°, D364 90° AlCrN, D365 142°, D365 142° AlCrN, plus 90° 4pc and 5pc sets and 120° 4pc set) and 1 Bordo (HSS Cobalt TiAlN). See the Spotting Drill Bits & Sets collection. For Sandvik Coromant, Iscar, Garr, Harvey Performance, OSG, Walter or Gühring, source through our supplier network on request.