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How Audio Parts Are Made: Machining and Forming Processes
The route a part takes decides its cost, what it can hold and which marks it carries into the finish. This page covers machining and forming. Anodize, brushing, blasting and marking have their own section in the finishing guides.
Process table
Typical ranges, not promises. Tolerance depends on part size, material and finish, and the shop that quotes you confirms what it can hold on your geometry.
| Process | Typical audio parts | Typical tolerance | What it means for the finish or cost |
|---|---|---|---|
| 3-axis milling | Faceplates, chassis plates, top covers from plate, connector panels | ±0.05 mm typical, ±0.02 mm on fits | Face milled surfaces show tool marks under anodize; specify the cosmetic face and its Ra |
| 4 and 5-axis milling | Headphone cups and yokes, sculpted knobs, tonearm bases, speaker cabinets | ±0.02 to ±0.05 mm typical | Fewer setups means fewer witness marks between faces |
| CNC turning | Knobs, feet, spikes, platters, trim rings, counterweights | ±0.02 mm on diameters typical | Concentric grain from facing reads as a cosmetic finish on its own |
| Swiss-type turning | Pins, tonearm bearing parts, cartridge screws, small terminals | ±0.01 to ±0.02 mm typical | Long slender parts from bar, economical at hundreds of parts and up |
| Diamond cutting | Mirror chamfers on faceplates and knobs, platter faces | Optical finish, Ra well under 0.1 µm achievable | Cut after anodize gives a bright edge on a dark panel; needs a rigid setup |
| Extrusion plus machining | Chassis side panels, heatsinks, trim profiles | Section per EN 755-9 or ANSI H35.2, machined features ±0.05 mm | Die cost is low next to billet once quantities pass a few hundred sets |
| Sheet metal | Folded covers, back panels, internal brackets, shields | ±0.2 mm on formed features typical | Cheapest enclosure route; bend lines and gaps need design care to look right |
| Die casting | High volume enclosures and heatsink housings | Per casting tolerance grade, machined faces ±0.05 mm | Casting alloys anodize poorly; usually powder coated or painted |
| Grinding and lapping | Platter bearing spindles, thrust faces, flat reference surfaces | Microns on diameter and flatness | Used where a turned surface cannot hold the runout or flatness |
Background on the core process: numerical control. Definitions of setup, fixture, witness mark and bow and twist are in the glossary.
Part feature to process
A quick way to see why a quote carries the operations it does. Most audio parts combine two or three of these.
- Flat cosmetic faceFace milling with a large cutter, or fly cutting, then blasting or brushing before anodize to hide tool marks. Machining thick front panels
- Bright edge on a dark panelDiamond cut chamfer after anodize. Diamond cut chamfers
- Round part with grainTurning, with the facing pass left as the finish or followed by brushing. Knurls are turned or milled. Volume knob machining
- Long constant sectionExtrusion cut to length, then machined for holes, slots and fits. Heatsink extrusions
- Thin wrap-around coverLaser or punch, then press brake. Sheet metal covers
- Threads in an anodized partTapped before anodize and masked, or threaded inserts fitted after. Threads in anodized chassis
- Rotating massTurning, then runout check and balancing. Turntable platter machining
- Small loose hardwareSwiss turning, then vibratory finishing in bulk. Vibratory finishing
What the route means for quantity
On cosmetic work the cutting time is often the smaller part of the bill. Setup, deburring, finishing, inspection and packing dominate, and they change less with quantity than buyers expect.
For the cost side in detail, see billet, extrusion or sheet and minimum order and lead time.
- 1 to 50 setsBillet milling and turning, no tooling. Highest unit cost, fastest to change.
- 50 to 500 setsDedicated fixtures, soft jaws and sometimes an extrusion die for chassis sides.
- 500 sets and upExtrusion and sheet metal take over from billet where the look allows. Die casting only at much higher volumes.
Questions about processes
Should my chassis be machined from billet, extruded or folded?
It depends on quantity and the look you want. Billet gives any geometry with no tooling but turns most of the plate into chips. Extrusion needs a die but brings unit cost down once you order a few hundred sets. Folded sheet is cheapest but shows bend lines and needs care at the gaps. Most chassis combine two or three of these.
What does diamond cutting add to a part?
A mirror bright facet, usually a chamfer on a front panel or knob, cut with a single crystal diamond tool. Cut after anodizing it shows bare bright aluminum against the coloured surface, so the edge is left unprotected unless it is lacquered or anodized again. Say on the drawing whether the cut is before or after anodize.
How are turntable platters balanced?
Platters are turned, then checked for runout and flatness and balanced by removing material at the heavy point or adding mass. Balance quality is usually written as a grade under ISO 21940-11, with the rotating speed of 33 1/3 or 45 rpm. Put the grade, flatness and runout limits on the drawing.
Can one shop make every part of my product?
Often several processes sit in one shop, typically milling and turning together, while extrusion, sheet metal and finishing come from partners it manages. Send the full set in one RFQ and say which parts must match in appearance. We match it with up to 3 shops whose machines and finishing fit, and reply within 24 business hours.
Not sure which route fits?
Send the drawing and the quantity. Shops in the match will say how they would make it. Materials: alloys and plastics. Parts: applications. Chassis in depth: chassis guides.