Malones CNC Machining Overview

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  How Malones CNC machining removes metal
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  Axes, setups and what each machine can reach
• 3
  Reading the material before quoting
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  Where ±0.005 mm holds and where it does not
• 5
  Cost drivers and honesty about limits
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  From upload to inspected parts
• 7
  When CNC machining is the right process

Malones CNC machining starts with a CAD model converted into toolpaths. The controller reads G-code and moves a spindle along X, Y and Z while a cutter, usually carbide, shears material away in chips. Nothing is cast or bent into shape. Material is subtracted, so the finished surface is whatever the tool left behind.

The cutting edge does the real work. Each tooth takes a bite set by feed per tooth, and the chip has to leave cleanly. Aluminum 6061 cuts at 200–400 m/min surface speed with a two or three flute cutter and no coolant on many jobs. 316 stainless runs far slower, often 60–120 m/min, because it work-hardens the moment the tool rubs instead of cuts.

Heat is the main enemy. Most of it should leave with the chip. If the spindle dwells, heat travels into the part and the part grows. A 100 mm aluminum block moves about 0.0023 mm per 1 °C of temperature change. That is small, but it is half our tolerance band, so we let parts settle before final measurement.

Rigidity decides finish. A short tool in a solid holder cuts quietly. A long tool hanging 5 × its diameter will chatter, and chatter shows up as Ra 3.2 μm or worse on a nominal Ra 0.8–1.6 μm callout. When a finish spec looks tight, we look at the tool stick-out first, not the feed rate.

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  Subtractive, not formingShape comes from tool motion, so complex pockets and radii are one setup, not a die.
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  Speeds are material-specificAluminum is fast, stainless and titanium are slow, plastics need sharp edges and high rake.
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  Heat leaves with the chipDwelling dulls the edge and pushes heat into the workpiece.

Axis count is a setup decision, not a quality ranking. A three-axis mill cuts from one direction, so every face needs a re-fixture. Each re-fixture adds stack-up error and handling time. A four-axis machine adds rotation about one axis, which suits shafts, bushings and parts with features on a cylinder.

Five-axis machines tilt the tool or the table, so the cutter reaches undercuts and angled faces without the part moving. We run 16 simultaneous five-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Mill-turn matters when a part is mostly round but has milled flats, cross holes or a slot. One machine finishes it, and concentricity stops depending on how well a fixture was reset.

Size sets the limit. Our largest travel is 4,000 × 400 × 150 mm, with a Ø400 mm rotary table on the five-axis side. Medium frames run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact cells cover 500 × 500 × 450 mm and 500 × 310 × 200 mm. A part that fits a compact cell usually gets better throughput.

Simultaneous five-axis means all axes move at once, keeping the tool normal to the surface. That is what makes a smooth contoured surface possible in one pass. Indexed five-axis, where the table locks between positions, is cheaper to program and fine for holes on several faces.

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  3-axisPrismatic parts, one dominant face, lowest hourly rate.
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  4-axisCylindrical parts with features around the diameter.
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  5-axis simultaneousContoured surfaces and undercuts, fewer setups.
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  Mill-turnRound part plus milled features, one chucking, better concentricity.

A drawing tells us geometry. The material line tells us whether the geometry is practical. Aluminum 6061-T6, 7075 and 2024 cut quickly and hold ±0.005 mm on stable features. Copper C110 and brass C36000 cut cleanly but move with temperature, so we plan a cool-down before the final pass.

Stainless 303 and 304 are common; 316L shows up in medical and marine work because of corrosion resistance. They machine differently. 303 has sulfur added for chip breaking and cuts well. 304 and 316L gum up on light passes, so the tool has to stay engaged. Titanium TC4 (Ti-6Al-4V) and Inconel sit at the hard end: low speeds, high tool wear, and a real risk of work hardening if the cutter stops moving.

Plastics behave unlike metal. POM and PEEK hold tight tolerances but trap heat at the cut, so sharp uncoated tools and air blast beat flood coolant. Acrylic (PMMA) cracks under clamping pressure. Carbon fibre eats cutting edges; we budget for more tool changes on those jobs.

Material choice also drives finishing. Anodizing suits aluminum, electroless nickel suits steel and copper alloys, and passivation suits stainless. A tight cosmetic spec on a soft alloy is harder than a tight dimensional spec on the same part.

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  Free-cutting grades6061, C36000, 303 stainless: good finish, predictable size.
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  Gummy grades304, 316L, pure copper: keep the edge engaged, avoid light rubs.
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  Hard gradesTC4, Inconel: slow speeds, short tool life, plan the cycle.
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  PlasticsSharp tools, air blast, light clamping.

±0.005 mm (about ±0.0002 in) is a shop-wide capability, not a default on every dimension. It holds on a 20 mm bore in 6061 with a reamed or bored finish, measured at 20 °C on a stable part. It does not hold across a 600 mm aluminum frame in an uncontrolled room, because thermal expansion alone uses the whole band.

Feature type matters more than nominal size. A ground or bored diameter holds tighter than a milled slot, because the tool is fully engaged and the load is even. A slot cut with a long end mill bends away from the wall, and the spring pass leaves a taper. Thin floors deflect upward. Deep holes drift.

Surface finish and tolerance travel together but are not the same callout. Ra 0.2–0.8 μm is a fine finish, usually from lapping or fine boring. Ra 0.8–1.6 μm comes off a well-run finishing pass, and Ra 1.6–3.2 μm is normal as-machined stock. A tight Ra on a loose dimension is easy. A tight Ra inside a deep pocket is not.

GD&T changes the picture. Position tolerance with a maximum material condition bonus can be met more easily than a flat ± number, because the bonus grows as the hole does. When a drawing mixes tight size limits with tight position on the same hole, cost climbs fast. Loosening one usually saves more than switching machines.

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  Stable featuresBores, ground diameters, short pockets: ±0.005 mm is realistic.
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  Long spansThermal growth dominates; specify a reference temperature.
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  Thin walls and floorsDeflection sets the real limit, not the machine.
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  Mixed GD&TTight size plus tight position is the expensive combination.

Setup count is the biggest cost lever on low volumes. A part that needs four faces machined from four directions pays for four fixtures and four alignments. Redesigning so three faces come off one five-axis setup often cuts cost more than shaving cycle time.

Volume changes the answer. Below roughly 1,000 units, machining usually wins because there is no tooling to amortize. Past 50,000 units, casting or molding takes over on unit price, and machining returns as the finishing step for critical bores and mating faces. There is no minimum order quantity here, from one prototype to 10,000+ part runs, so the crossover is a cost question, not an access question.

Some geometry just does not machine. Closed internal channels, lattice structures and parts with internal voids need additive or casting. We say so at the DFM stage rather than quoting a job we cannot hold.

Inspection is not optional on tight work. We run raw material checks, in-process monitoring and final inspection, with a 99.99% qualification rate across production runs. For a part at ±0.005 mm, the measurement plan is part of the process, not a formality at the end.

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  Fewer setups, lower costRedesign for one or two fixturings when volume is low.
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  Volume crossoverMachining under ~1,000 units; casting past 50,000.
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  Not machinableClosed channels and lattices need another process.
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  Measurement planTight tolerance work needs a defined inspection method.