Best Drill For Inconel 600 Small Drill

For small-diameter holes in INCONEL 600, the highest probability of success (longer tool life, better hole quality, fewer broken tools) comes from using short, rigid, solid-carbide micro-drills (micro-grain carbide, with PVD coatings such as TiAlN or AlCrN) sized for the hole, run at low surface speed, steady chip load, and with through-tool or high-pressure coolant plus frequent pecking to evacuate chips. When carbide is not available for tiny pilot holes, cobalt-enriched HSS (M35 / M42) can be used as a backup for low-volume work, but carbide with proper coolant and machine setup is the preferred production solution.

Why INCONEL 600 is difficult to drill

INCONEL® 600 (UNS N06600) is a nickel-chromium-iron alloy engineered for corrosion and high-temperature resistance. Its metallurgy gives it high strength, toughness and a tendency to work-harden in front of the tool. Thermal conductivity is low compared with steels, so heat generated at the cutting edge stays concentrated in the cutting zone and the tool. Those three features combine to accelerate tool wear, increase cutting temperatures, and promote built-up edge or premature fracture of small drills. Tool manufacturers and alloy datasheets make these traits clear and are the foundation for the recommendations below.

Key outcomes for the machinist:

• high cutting temperature at the tool tip;

• strong adhesive wear and diffusion wear modes;

• easy work-hardening if feed is too light or the tool dwells;

• chip evacuation problems when using small drills or deep holes.

Small-diameter drilling — special problems and failure modes

Small drills (typically for diameters under ~6 mm / 0.25") bring additional constraints:

• Low stiffness. Small drills deflect more, increasing the chance of rubbing and chatter.

• Heat buildup because small drills have less cross-section to carry heat away and often lack internal coolant.

• Chip packing inside the flute: when chips cannot escape they collapse the flute, seize the tool, or break the drill.

• Work hardening ahead of the tool: if feed is insufficient, the surface work-hardens and quickly wears the cutting edge.

• Runout sensitivity: even 0.01 mm runout can severely reduce the life of a micro-drill in Inconel.

Because of these failure modes, the right combination of tool material/geometry, coolant strategy, and process control is essential.

Best drill materials and geometry for small holes

Preferred tool material (production / highest reliability)

Solid micro-grain carbide (fine-grain WC) — marginless or with engineered margins. For small-diameter holes the most consistent production results come from purpose-built solid-carbide micro-drills offered by major tool makers (examples: Kennametal GOdrill family, Sandvik CoroDrill variants for HRSAs). These drills give superior hot-hardness, edge retention and rigidity for the tiny geometries involved. Choose micro-grain carbide grades intended for heat-resistant superalloys.

Backup for prototypes / low volumes

Cobalt-enriched HSS (M35 / M42) — can be used for pilot holes or where carbide micro-drills are unavailable. HSS is tougher but wears faster in high temperatures; expect shorter life and more frequent sharpening. HSS is also easier to resharpen for small shops.

Tip geometry and point angle

• Split point / parabolic split (self-centering) at around 135° to 140° reduces thrust and helps start the hole without a pilot in many applications.

• Web thinning and reduced chisel edge help keep thrust low for small diameters.

• Short flute lengths and a strong, stiff web are preferred (short overhang). Extended lengths drastically raise deflection risk.

Flute count

• For very small diameters (≤ 2 mm) 2-flute twist designs are typical — they maximize flute volume for chip evacuation and provide large cutting edges.

• For slightly larger micro-drills (2–6 mm) specialized 3- or 4-flute micro designs can be used to increase rigidity and feed handling, but flute geometry must prioritize chip evacuation.

Manufacturer-designed micro drills (not generic jobber drills) are recommended because their geometry, helix angle and split-point design are tuned to the demands of HRSA (heat resistant super alloy) drilling.

Coatings, coolant and chip control

Coatings

• TiAlN (Aluminium-rich PVD) and AlCrN coatings are commonly recommended for nickel alloys because they raise the thermal barrier at the cutting edge and resist diffusion wear. These coatings also help when intermittent contact or rubbing occurs.

• For deep or difficult holes look for coating + substrate combinations specified by the tool maker for HRSA work.

Coolant strategy

• Through-tool coolant (internal coolant) is the most effective single improvement for small-hole drilling in Inconel: it supplies lubricant and coolant directly to the cutting edge and helps evacuate chips. Many carbide micro-drills are available with through-coolant capability.

• If through-coolant is not possible, use high-pressure external coolant (HPC) directed into the flute and aggressive air blast / chip breaker methods. Flood coolant is better than dry; dry drilling accelerates wear and increases seizure risk. Sandvik and other tool houses advise lowering speed and ensuring strong coolant flow for difficult materials.

Chip control and peck drilling

• Short peck cycles prevent chips from collapsing the flute and reduce dwell time that causes work-hardening. For micro drills, peck depth may be very small (fractions of mm) and peck frequency high (many pecks per hole), which is normal.

• Use chip breakers on the drill where available and program dwell only when necessary — dwell often hurts Inconel because it causes local work-hardening.

Practical speeds, feeds and peck strategies (starting points)

Tool manufacturers publish specific SFM/RPM and feed recommendations for each tool and diameter. Always validate with the tool maker’s calculator for your exact drill and machine. That said, these industry-backed starting ranges reflect real shop practice:

• Surface speed (SFM): small-diameter drilling in Inconel commonly starts low — typical practical production starting values fall between 50 and 120 SFM (16–37 m/min) depending on tool material and coolant capability. For carbide drills with through-coolant you may use the higher end after validation; for HSS start at the lower end.

• Feed per revolution (chip load): use the tool maker’s chip-load chart. For micro-drills, feeds are small but must be sufficient to avoid rubbing: a typical chip load might be in the order of 0.0005"–0.004" per rev (0.01–0.10 mm/rev) depending on diameter and tool recommendation. Under-feeding causes work-hardening; over-feeding breaks the micro-drill.

• Peck depth: for small holes, peck depths can be 0.5–2 × D when flute volume is good, but many shops use much shallower pecks (e.g., 0.2–0.5 mm) for diameters <2 mm. The goal is to evacuate chips reliably without creating long, continuous chips that jam the flute.

• Peck dwell: avoid dwell at bottom whenever possible. If a dwell is required for centering, keep it brief; then retract to clear chips.

• Coolant pressure: maximize what your tooling supports. Through-tool or 70–150 bar HPC is beneficial for hole quality and tool life in production; for small shops, aggressive flood with directed nozzles is the minimum.

Important practical rule: run a conservative starting parameter from your tool maker’s feed & speed generator and then increase feed (not speed) incrementally to find the stable, high-production point — feed helps prevent work-hardening in Inconel.

(If you need exact RPM for a given drill diameter, use: RPM = (SFM × 3.82) / diameter (in inches). Kennametal and Sandvik provide online calculators and charts — always follow the tool-specific numbers.)

Machine setup, toolholding and runout control

Small-hole drilling demands a rigid machine setup:

• Minimize tool overhang — keep the drill as short as possible relative to its diameter.

• High-precision collets or shrink-fit holders are preferred for micro-drills; ER collets are common but shrink holders give the best concentricity for production.

• Check runout at the tool tip — total indicated runout should be less than 0.001" (0.025 mm) for micro-drilling in super-alloys. Excessive runout dramatically shortens life.

• Part clamping must eliminate vibration and movement; consider vacuum, hydrostatic clamps or multiple vises for thin parts.

• Stable spindle and low spindle speed variation — avoid intermittent climb/cut changes that cause tool shock.

Step-by-step recipe for a successful small hole (example: Ø2.0 mm hole in INCONEL 600)

This is a reproducible starting procedure for a small production run; tune using tool maker data.

Assumptions: solid micro-grain carbide 2.0 mm drill, TiAlN PVD coating, through-coolant available, rigid CNC with good toolholding.

1. Tool & holder: use shrink-fit or precision collet, check runout (< 0.01 mm). Use a short-length micro drill with through-coolant.

2. Pilot/spot: spot drill or center drill briefly at low speed (use a solid carbide center drill) to ensure correct position and reduce wandering.

3. Initial parameters: pick starting SFM = 60 SFM (≈ RPM = (60 × 3.82)/0.0787" ≈ 2910 RPM) — calculate precisely for your unit conversion. Starting chip load ~0.02 mm/rev (adjust by tool chart). Use through-coolant at 20–70 bar if available. If you cannot use through coolant, use maximum flood and a 90–120 bar external nozzle if your setup allows.

4. Peck cycle: peck depth = 0.25–0.5 mm, retract to break chip and clear flute; no dwell at bottom. Repeat until depth reached.

5. Monitoring: watch chips — they should be short segments or powder, not long stringy chips. Monitor spindle load and listen for chatter. If chips turn stringy or load climbs, reduce RPM and increase peck frequency.

6. Finish pass (if required): if a high surface finish or precise hole size is required, consider a reaming operation or a final light peck pass with slightly reduced feed to avoid work-hardening.

7. Tool inspection: after the first few holes, inspect the edge under magnification — look for flank or crater wear and micro-chipping. Replace before catastrophic fracture.

This recipe is a starting point: validate and refine with the tool maker’s feed & speed tables, and with a first-article run.

Comparison table: recommended drills by diameter and run size

(Entries reflect manufacturer product families and field practice; pick exact grade/geometry per the tool maker and the required hole tolerance.)

Maintenance, inspection and quality checks

• Check tools visually after fixed intervals (holes produced or minutes of cutting). Replace or resharpen before catastrophic chipping.

• Measure hole size and roundness — Inconel’s spring back and work hardening can affect final geometry.

• Record tool life for the job and build a tool-change schedule. Inconel will vary lot to lot; tracking helps predict costs.

• Keep tool-holders clean and collets free of debris — dirty interfaces increase runout.

FAQs

1. Can I use standard jobber HSS drills for small holes in INCONEL 600?
   You can for occasional prototypes, but expect very short life and poorer hole quality; for production, use micro-grain carbide or M35/M42 cobalt HSS as a last resort.

2. Is through-coolant essential for small holes?
   It is highly recommended. Through-coolant greatly improves chip evacuation and tool life; if not possible, use high-pressure external coolant and very aggressive pecking.

3. What coating should I choose?
   TiAlN or AlCrN PVD coatings are common choices for HRSA drilling; they improve edge temperature resistance and reduce diffusion wear.

4. Should I peck or use continuous plunge?
   Peck is recommended for small diameters to avoid chip build-up; keep pecks shallow and frequent for micro drills.

5. What causes immediate drill breakage?
   Typical causes are excessive overhang/deflection, runout, under-feeding (work-hardening), or chip jam in the flute. Fix those before changing speeds.

6. Any special geometry to avoid?
   Avoid long chisel edges and large web thickness on micro drills; choose web-thinned, split-point geometries tuned for HRSA.

7. What SFM/RPM should I start with?
   Start conservatively (≈ 50–80 SFM) and adjust; use the tool maker’s feed & speed tool for precise RPM for your diameter.

8. How to improve hole surface finish?
   Use a dedicated finishing drill or reamer, ensure stable setup, and avoid dwell at the bottom of pecks to prevent work-hardening.

9. Are special lubricants required?
   Use high-performance soluble oils or synthetics designed for nickel alloys; manufacturer recommendations vary — do not use standard cutting fluids meant only for steels.

10. How do I choose between carbide and HSS?
    Choose carbide for production and where rigidity/coolant is available; HSS (M35/M42) only when carbide micro-drills are unavailable or for low-volume jobs.

Authoritative references

• INCONEL® alloy 600 — Special Metals technical bulletin (material properties)
• Guidelines for the welded fabrication and handling of nickel alloys — Nickel Institute (technical guidelines including machining notes)

Final notes

• Use manufacturer-matched drill, grade and coating whenever possible; their feed & speed tools are made for each part number.

• For small diameters, prioritize rigidity, coolant at the edge, and sufficient feed — those three variables beat arbitrary increases in spindle speed.

• Keep a short, documented first-article process sheet: tool number, holder type, runout, coolant pressure, SFM, feed/rev, peck depth, observed tool life. That data will save time when scaling up.