# Machining CuCrZr (C18150) on a Hobby CNC A reference for milling copper-chromium-zirconium alloy on small-format CNC machines (Milennium Milo, Voron Cascade, and similar), with specific focus on producing nickel-plated 3D printer heat blocks compatible with the Slice Engineering FIN nozzle standard (M5×0.8). --- ## About the Material **UNS C18150 / CuCr1Zr / CW106C / RWMA Class 2** — a precipitation-hardening copper alloy combining high thermal/electrical conductivity with mechanical strength at elevated temperatures. The premium copper alloy for 3D printer heat blocks, also widely used for resistance welding electrodes, EDM electrodes, and high-performance heat sinks. ### Composition (nominal) - Copper: ~98.85% - Chromium: ~1% - Zirconium: ~0.15% ### Key properties | Property | Value | |---|---| | Thermal conductivity | ~320 W/m·K | | Electrical conductivity | 45–60% IACS | | Density | 8.89 g/cm³ | | Tensile strength (peak-aged) | 410–500 MPa | | Hardness (peak-aged) | ~200–250 HV | | Max service temperature | ~500°C | | **Machinability rating** | **~20** (vs. 100 for free-machining brass) | ### Why it's used for 3D printer hotends - ~80% of the thermal conductivity of pure copper - Retains mechanical properties at hotend temps (where pure Cu anneals and creeps) - Holds threads under repeated thermal cycling - Precipitation-hardens — can be machined soft, then aged to final hardness - Universally nickel-plated for surface durability and filament release --- ## Why It's Hard to Machine CuCrZr is one of the most challenging materials a hobby machinist will encounter. The machinability rating of ~20 means it removes roughly five times slower than free-machining brass for the same tool life. Specific problems: - **No chip breaking.** Chromium and zirconium precipitates strengthen the alloy without disrupting chip formation. Chips come off in long continuous ribbons that wrap around the tool. - **Work hardening.** Each pass leaves a hardened surface that the next pass must cut through. - **Built-up edge.** Copper welds to hot tool surfaces, ruining finish and accelerating wear. - **Gummy behavior.** Even in peak-aged state, it deforms and smears rather than shearing cleanly. - **Heat retention.** High conductivity means heat goes everywhere — into the workpiece, tool, and machine — rather than concentrating in chips. Expect to spend real time dialing in your process. Commercial shops describe months of development to reliably get chip breaks; home-machinist reality is generally accepting the long chips and working around them. --- ## General Machining Strategy ### Heat-treatment state matters - **Solution-annealed ("W" temper):** softer, slightly more cooperative chips, but very gummy. - **Peak-aged ("TH04" / T8 temper):** harder, holds dimensions better, the state finished parts ship in — and the worse one to machine. - **If possible:** machine in annealed state, then send out for aging post-machining. For one-off hobby work, accept the as-supplied (usually peak-aged) state. ### Toolpath philosophy - **No slotting.** Always adaptive/trochoidal with light radial engagement. - **Climb mill only.** Conventional milling builds up edge immediately. - **Constant motion.** No spindle stops mid-cut. No dwells. No rubbing. - **Light radial, generous axial.** 5–10% of diameter radial, 1–2× diameter axial. - **Short stickout.** Maximum tool rigidity always. ### Coolant - **Flood ideal.** Heavy mist (Lube Cube class HVLP) is workable but inferior. - Aim coolant directly at the cutting edge, not the chip pile. - Use a coolant rated for copper (some sulfur-containing oils stain it). - Compatible options: Hangsterfer's S-500, Blaser Blasocut, Rustlick G-25J. --- ## Tooling Recommendations All recommendations are 1/8" (3.175 mm) shank suitable for ER16 collets on the Milo or Cascade. ### Geometry requirements (non-negotiable) - **2 or 3 flute only.** More flutes pack chips and break tools. - 3-flute: HSM/adaptive work - 2-flute: slotting, finishing - **Aluminum/non-ferrous geometry.** Positive rake, high helix (40°+), polished flutes. - **Coatings:** uncoated polished carbide, ZrN, or DLC. - **Avoid:** TiN, TiAlN, AlTiN — designed for steel; copper sticks aggressively to these. - **Stub or regular length only.** No long-reach tools. ### Endmills — best balance of quality and price | Tool | Description | Approx. price | |---|---|---| | **Lakeshore Carbide AlumaCut 3-flute, 1/8"×1/8"** | ZrN coated, polished, USA made, stub available | $20 | | **Performance Micro Tool TR-2-1250-S** (or 3-flute) | Polished flutes for non-ferrous | $25–35 | | **Kyocera SGS Z-Carb AP, 1/8"** | Variable pitch, ZrN, good chatter behavior | $30–40 | ### Endmills — premium tier | Tool | Description | Approx. price | |---|---|---| | **Datron 00684xxx single-flute polished** | Reference for small-tool non-ferrous; single flute = max chip clearance | $40–80 | | **Helical Solutions HEV-AL-3, 1/8" 3-flute** | Variable helix, ZrN | $40–60 | | **Harvey Tool 50300-C3** (copper/aluminum line) | Deep micro-tool catalog | $35–55 | ### Endmills — budget / starter tier | Tool | Description | Approx. price | |---|---|---| | **Drillman1 (eBay) "AlumiSharp" polished carbide** | Decent uncoated polished, hobby standard | $8–15 | | **SpeTool / Yonico (Amazon)** | Variable quality; OK for first attempts | $5–10 | ### Drills (carbide only; HSS will not survive) - **OSG ADO solid carbide stub drill series** - **Harvey Tool miniature carbide drills** - Uncoated or ZrN, parabolic flute - Spot drill first with 90° or 120° spot - Peck drill with full retract every 0.5× drill diameter ### Reamers - **Solid carbide chucking reamer** (Hertel, MariTool, etc.) - Leave 0.05–0.1 mm stock for the ream - Drilled holes in CuCrZr will not be round or smooth ### Thread mills (M5×0.8 for FIN) **Single-profile only** — multi-profile/full-form mills cut all threads simultaneously and produce too much engagement for this material. | Tool | Description | Approx. price | |---|---|---| | **Harvey Tool 70816-C3** (or equivalent single-profile 0.8 pitch) | Solid carbide, uncoated or ZrN | $50–80 | | **Carmex MTS 0.8 ISO M3-D single-profile** | Industrial thread-mill standard; 1/8" shank available | $40–60 | | **Vargus / Helical Solutions / Walter equivalents** | Helical TM3 series is well-regarded | $40–80 | | **Maritool TMS series (USA)** | Reasonable price, single-profile | $30–40 | | **Drillman1 eBay imports** | Variable quality, useful for process development | $15–25 | ### Inspection - **Class 6H M5×0.8 thread plug gauge** (Vermont Gage or similar): ~$30 - Sacrificial nozzle as functional gauge: cheaper but less precise --- ## Cutting Parameters Starting points for a 1/8" tool on the Milo at 24k spindle. Refine empirically. ### General milling (3 mm 3-flute, HSM/adaptive) | Parameter | Value | |---|---| | SFM | 250–350 | | RPM | 12,000–18,000 | | Chip load | 0.0008–0.0015 in/tooth | | Radial DOC | 5–10% of tool diameter (0.15–0.3 mm) | | Axial DOC | 1–2× tool diameter (3–6 mm) | | Direction | Climb only | ### Thread milling (3 mm single-profile, M5×0.8) | Parameter | Value | |---|---| | RPM | 12,000–15,000 | | Feed | 200–300 mm/min | | Passes | 3–5 light radial passes | | Step per pass | ~0.05 mm radial | | Direction | Climb (G3 for right-hand internal) | | Coolant | Flood or heavy mist | ### Drilling | Parameter | Value | |---|---| | Approach | Spot drill → peck drill | | Peck depth | 0.5× drill diameter | | Retract | Full retract each peck | | Coolant | Flood; flush chips actively | --- ## Process: FIN-compatible Heat Block (Worked Example) The Slice Engineering FIN standard specifies **M5×0.8 threads, 4.4 mm thread length, in a 9.5 mm overall nozzle.** The block needs the matching internal thread plus FIN's published seal-face and boot-interlock geometry. ### Step-by-step 1. **Spot drill** the nozzle location: 90° or 120° carbide spot drill, establishes position and creates lead-in chamfer. 2. **Drill** to ~3.5–4.0 mm with carbide stub drill. Peck deep, full retract, flood coolant. Do not drill to final minor diameter — bored or reamed holes are required for roundness. 3. **Bore or ream** to 4.17–4.20 mm. M5×0.8 minor diameter is 4.134 mm; we want a few thou above that to give the thread mill clean working room and account for plating thickness (see below). 4. **Mill the FIN seal-face geometry** to spec. Reference Slice Engineering's published FIN drawings — the seal face does the actual filament containment, not the threads, and its finish and concentricity matter more than the thread fit. 5. **Thread mill in 3–5 passes.** Start with the cutter just kissing the bore, increase radial offset by ~0.05 mm per pass. Climb mill (helical interpolation, G3 for RH internal). Gauge between passes. 6. **Verify with thread plug gauge** before declaring done. Sacrificial nozzle as backup. 7. **Mill the boot-interlock features** per FIN spec. 8. **Surface polish/lap** key features before plating. Plating exaggerates surface defects rather than hiding them. 9. **Send out for electroless nickel plating.** Specify the thickness so it can be accounted for in your thread offset. ### Gotchas - **Plating thickness changes thread fit.** Electroless nickel adds ~10–25 µm per surface, which means ~20–50 µm reduction in minor diameter after plating. Mill threads toward the top of the 6H tolerance band so the as-plated fit is correct, not the as-machined fit. **Expect 1–2 iterations** to dial in the offset for your plater. - **Don't omit FIN's non-thread features.** The standard's value is in the boot interlock and thermal-expansion-tolerant seal — threads alone don't make it FIN-compliant. - **Buy endmills in threes.** First tool teaches you the material, second tool cuts the part, third is the backup. The first one usually dies learning what doesn't work. - **Watch for built-up edge.** If finish degrades mid-cut, copper has welded to flutes. Pull tool, clean with brass brush, or strip with brief acid dip. - **Listen for the song change.** CuCrZr telegraphs tool failure with a higher-pitched whine before letting go. Retract and inspect at any tone change. ### Starter tooling kit (~$150 budget) - 1× Lakeshore 3-flute 1/8" endmill (roughing) - 1× Lakeshore or Datron 2-flute 1/8" endmill (finishing) - 1× 4.0 mm carbide stub drill - 1× 4.17 mm chucking reamer - 1× Carmex or Harvey single-profile M5×0.8 thread mill - 1× Class 6H M5×0.8 thread plug gauge - Coolant: Hangsterfer's S-500 or equivalent This is enough to attempt a first FIN heat block end-to-end. Budget for breaking the first one or two tools while learning the material. --- ## Further Reading - Slice Engineering — *FIN: The Complete Guide* (sliceengineering.com/blogs/news/fin-the-complete-guide) - Copper Development Association — C18150 datasheet (copper.org) - FM Carbide — *Machinability of C18150 Copper Alloy* (fmcarbide.com) - Weldaloy — C18150 mechanical properties reference