proc_cnc_milling

CNC Milling

subtractive · computer numerical control milling, 3-axis milling, 5-axis milling

A computer-controlled cutter removes material from a block. Precise, repeatable, expensive, slow. The default for one-off metal parts and the way most prototype enclosures get made. The renato.design CAM tool for this process is *swarf* — a focused interface over Kiri:Moto for design students, configured for the Langmuir MR-1 and ShopBot Basic, with a locked tool inventory and four-operation student mode. STL in, verified G-code out, no general-purpose CAM detour.

Multi-axis subtractive process using rotating cutting tools along programmed toolpaths. Tolerances commonly ±0.025mm in 3-axis, ±0.013mm in 5-axis.

Scale & Tolerance

  • scale (mm)0.1 – 2000
  • tolerance (mm)0.025
  • skillintermediate to advanced — CAM software literacy required
  • min skilladvanced
  • whereschool shopprofessionalindustrial
  • costhigh per part at low volume, drops with batching

Equipment

  • school_shopyes — Tormach, Bridgeport with CNC retrofit, Bantam desktop
  • professionalHaas, Mazak, DMG Mori
  • industrial5-axis Hermle, Matsuura, Makino

Environmental

  • energy_usemoderate to high
  • waste_streamchips — recyclable for metals, landfill or grind-and-reuse for plastics
  • consumablescutting fluid, end mills

Cost over volume

1101001k10k100k1M0.010.1110100100010000units (log scale)total cost (relative, log scale)

Numbers are relative ratios, not dollars. The crossover point matters more than the magnitude. Anchored to injection molding + ABS = 1.0.

Trade-offs

constraints · what is lost · what is gained
PMMA (Acrylic)
  • constraints
    • internal corners limited to tool radius (most aggressive: 0.5 mm end mill)
    • deep narrow pockets need tools with reach > 4× diameter (tool deflection becomes the limit)
    • thin walls (<1 mm) chatter under cut
    • no compound-curved internal cavities without 5-axis
  • what is lost
    • tool path register is visible on the cut surface — tooling marks read as design language or defect, depending
    • polished optical clarity requires flame-polish or vapor-polish post-pass
  • what is gained
    • one-off and small-batch economic without tooling investment
    • tolerances ±0.025 mm on 3-axis; ±0.013 mm on 5-axis
    • form revisions same day — no tooling lead time
ABS (Acrylonitrile Butadiene Styrene)
  • constraints
    • ABS is gummier than PMMA on the cut — needs sharper tools and more coolant
    • thin walls flex under cut, dimensional accuracy suffers below 1 mm wall
  • what is lost
    • matte tool-cut surface; not visually equivalent to injection-molded ABS finish
  • what is gained
    • prototype geometries that will eventually be injection molded — material match, geometry-equivalent
    • machinable inserts and snap-fit prototypes
Aluminum 6061
  • constraints
    • internal corners limited to tool radius
    • thin walls < 1 mm chatter on aluminum unless backed
    • deep pockets need flood-coolant evacuation
    • no compound internal geometry without 5-axis
  • what is lost
    • anodizing-uniformity depends on tool-path direction — visible swirl unless surface is uniformly oriented
  • what is gained
    • tolerances ±0.025 mm 3-axis, ±0.013 mm 5-axis
    • the canonical metal prototyping process — strong-enough parts in a single setup
    • fixturing setup amortizes across short runs without true tooling investment

Plain language. Neutral framing — perfection is contextual, defined by use. Cf. Winchester, The Perfectionists (HarperCollins, 2018).

Simon Winchester (living — quote)

It is filled with gears that allow for the adjustment of the tool or tools to tiny fractions of an inch, to permit the exact machining of the parts to be cut.

Winchester, *The Perfectionists: How Precision Engineers Created the Modern World* (HarperCollins, 2018), Chapter 2, 'Extremely Flat and Incredibly Close'. On Henry Maudslay's slide rest — the screw-driven tool carriage on the lathe that made tolerance-controlled metal cutting possible, and from which every modern CNC machining center descends.
Greg Lynn (living — quote)

The connection of disparate surfaces by co-planarity or blushing generates 'teething' across surfaces. The term 'teeth' describes any connection where surfaces are tangent or have coincident control vertices.

Greg Lynn, on the 'teeth' technique used in projects including *Tadpoles* (a desk and shelving system that uses teething to integrate multiple functional surfaces into a continuous, modulated form), as quoted in Schröpfer, *Material Design: Informing Architecture by Materiality* (Birkhäuser, 2011), Chapter 5, footnote 8. The teething operation generates the geometry that CNC milling then realizes — Lynn's *Predator* installation alone required 250 CNC-milled foam panels to serve as molds. Greg Lynn (b. 1964, founding partner Greg Lynn FORM, Los Angeles; Studio Professor at UCLA AUD; Full Professor at the University of Applied Arts Vienna) verified living 2026-04-28.
Compatible materials
Aluminum 6061
PMMA (Acrylic)
ABS (Acrylonitrile Butadiene Styrene)
Purple Gold (AuAl2)
Alumina (Aluminum Oxide, Al₂O₃)
Aluminum 2024
Aluminum 6063
Aluminum 7075
Aluminum A356 (Cast)
Aluminum Extruded L-Angle (Structural)
Aluminum Extruded U-Channel (Structural)
Aluminum T-Slot Extrusion, 1010 / 25mm Imperial Series (80/20-style)
Aluminum V-Slot Extrusion, 2020 (OpenBuilds-style)
White Ash (Fraxinus americana)
Laminated Bamboo
Baltic Birch Plywood
Cartridge Brass (C26000)
Bearing Bronze (C93200, SAE 660)
Aluminum Bronze (C95400, Sculpture / Marine Cast Bronze)
Carbon Fiber (T700, in epoxy)
Cast Iron, Gray (ASTM A48)
Western Red Cedar (Thuja plicata)
American Cherry (Prunus serotina, Black Cherry)
Copper C11000 (Electrolytic Tough Pitch)
Corian (Solid Surface — Acrylic + Alumina Trihydrate)
Natural Cork
Douglas Fir (Pseudotsuga menziesii)
Expanded Polystyrene Foam (EPS)
EVA Foam (Footwear Midsole / Crocs Croslite-Family)
Fiberglass (E-Glass, in epoxy or polyester)
G10 / FR4 (Fiberglass-Epoxy Laminate)
14k Green Gold
Pure Gold (24 karat)
14k Rose Gold
18k Rose Gold
18k White Gold (Palladium-Whitened)
14k Yellow Gold
18k Yellow Gold
22k Yellow Gold
Magnesium AZ31B
Mahogany (Swietenia macrophylla, Honduran / South American)
Hard Maple (Sugar Maple, Acer saccharum)
MDF (Medium-Density Fiberboard)
Niobium (Pure)
White Oak (Quercus alba)
Palladium 950 (Pd950)
PEEK (Unfilled)
PETG (Glycol-Modified PET)
Phenolic Resin (Phenol-Formaldehyde, Bakelite)
Eastern White Pine (Pinus strobus)
PLA (Polylactic Acid)
Platinum 900 / Iridium 100
Platinum 950 (Pt950)
Marine Plywood (BS 1088 / Mahogany or Okoume Veneer)
Polycarbonate (PC)
Porcelain
Polytetrafluoroethylene (PTFE)
Silicon (Electronic-Grade Single Crystal)
Argentium Silver 935
Argentium Silver 960
Fine Silver (999)
Sterling Silver (925)
Soapstone
Stainless Steel 17-4 PH
Stainless Steel 304
Stainless Steel 316L
Steel 1018 (Mild Steel)
Steel 4130 (Chromoly)
Steel, Seamless / DOM Tubing for Furniture (chrome-plated)
Tantalum (Pure)
Teak (Tectona grandis)
Titanium Grade 1 (CP-Ti)
Titanium Grade 2 (Commercially Pure)
Titanium Grade 5 (Ti-6Al-4V)
Titanium Grade 9 (Ti-3Al-2.5V)
Tungsten (Pure / Tungsten Carbide)
American Black Walnut (Juglans nigra)
Extruded Polystyrene Foam (XPS)
Zirconium (Reactor / Industrial Grade, Zr 702)

Second life

reversibilitylow — material removed by cutting is gone; chips are recycled separately.
output recyclabilityyes
waste streams
  • metal chips — recyclable scrap, sold by weight
  • plastic chips — landfill or grind-and-reuse for some thermoplastics
  • spent cutting fluid — hazardous-waste stream
  • worn end mills and inserts — carbide recycling exists at industrial scale
repair compatible withproc_adhesive_bonding, proc_tig_welding, proc_mig_welding

Editorial pass 2026-04-28.

Citations

  • book · Lefteri, *Making It: Manufacturing Techniques for Product Design*, 2nd ed. (Laurence King, 2012), 'Machining' p. 18, 'Computer Numerical Control (CNC) Cutting' p. 21.
  • url · https://en.wikipedia.org/wiki/Milling_(machining)
  • url · https://en.wikipedia.org/wiki/Numerical_control
  • url · https://tormach.com/
  • book · Winchester, *The Perfectionists: How Precision Engineers Created the Modern World* (HarperCollins, 2018), Chapters 1–2 — Wilkinson's cylinder-boring machine (1774, ground a 72-inch cylinder true to 'the thickness of an old sixpence') and Maudslay's slide-rest lathe (c.1797) as the precision-machining lineage from which CNC milling descends.