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Billet, Extrusion or Folded Sheet: Choosing How to Build a Chassis

August 8, 2026

Three processes build almost every audio enclosure. Most products use two or three of them together, and the decision is made early enough that it is worth understanding before the CAD is finished.

Billet machining

Material starts as solid plate or bar and the shape is cut out of it.

Strengths

• Any geometry, no tooling, no lead time beyond the shop’s queue
• Crisp edges, sharp chamfers, pockets and blind features
• One alloy through the whole part, so anodize behaves predictably
• The design can change between batches at no tooling cost

Weaknesses

• Most of the material becomes chips. On a front panel you may buy three kilograms to ship one.
• Cost per part falls slowly with quantity because cycle time dominates
• Large flat parts can move as material is removed, so thin panels need a stress relief or a two stage machining plan

Right for: front panels, knobs, platters, small enclosures, anything below a few hundred units, anything where the shape is the product.

Extrusion

Heated aluminum is pushed through a steel die, producing a continuous profile that is then cut to length and machined.

Strengths

• Very low cost per length once the die exists
• Fin geometry that is impossible or absurdly expensive in billet, which is why every serious heatsink is extruded
• Consistent cross section along the whole length
• 6063 and 6060 anodize brilliantly

Weaknesses

• Die cost and die lead time, typically six to ten weeks for a first article
• Cross section is fixed. Every feature that varies along the length is a secondary machining operation.
• Extrusion tolerances are looser than machining tolerances. Expect flatness and twist that must be machined out on mating faces.
• Thin tall fins have minimum thickness and spacing limits set by the extruder

Right for: heatsinks, sleeves, chassis bodies, rails, anything with a constant cross section above roughly 200 units.

Folded sheet

Flat sheet is cut by laser or punch, then bent on a press brake.

Strengths

• Cheapest way to enclose a volume
• Fast, widely available, low tooling
• Light

Weaknesses

• Bend radius is visible and limits how crisp an edge can look
• Tolerances across a folded part accumulate. A box folded from one blank can be a millimetre out of square without anything being wrong.
• 5052 and 5754 anodize to a different tone than 6000 series
• Sheet surface texture differs from a machined surface, which shows after anodize

Right for: covers, bottom plates, back panels, internal brackets, chassis bodies on price sensitive products.

Cost behaviour

	1 to 10	30 to 100	200 to 500	1,000+
Billet	Highest, setup dominates	High, competitive at this range	Falls slowly	Usually beaten by other routes
Extrusion	Not viable, die cost	Stock profiles only	Competitive, die pays back	Cheapest by a wide margin
Sheet	Low, laser needs no tooling	Low	Low, consider hard tooling	Lowest for simple shapes

The honest summary for a boutique brand: billet plus stock extrusion plus folded sheet, with a custom die only when the product has proved itself.

Mixing the three without it showing

Almost every good looking amplifier is a mixture. The craft is in making the joints deliberate.

1. Do not butt a billet face directly against an extruded face in a visible plane. The two will never be exactly coplanar or exactly the same colour. Put a shadow gap, a step or a chamfer between them so the eye reads a line rather than a mismatch.
2. Let the machined part be the reference. Machine the mating faces of the extrusion after cutting to length, so the panel sits against a machined surface rather than an extruded one.
3. Bead blast everything to the same grit before anodize. This does more to hide alloy differences than any other single step.
4. Go dark. Black hides alloy difference. Clear and champagne advertise it.
5. Hide the fasteners or make them a feature. Half hidden screws look like a compromise. Fully concealed or deliberately exposed both look designed.

A typical boutique build

• Front panel: 10 mm 6061 billet, machined, brushed, black anodized. The one part where money is well spent.
• Side heatsinks: stock 6063 extrusion, cut to length, faces machined, bead blasted, black anodized in the same load as the panel.
• Top and bottom: 1.5 mm 5052 folded sheet, bead blasted, black anodized.
• Back panel: 3 mm 6061 plate, machined for connectors, bead blasted, black anodized.
• Feet: turned 6061 or brass.

Five parts, three processes, one finish load. That is a chassis a small brand can actually make and repeat.

Questions to answer before you commit

• How many units this year and in three years
• Does any part need a cross section that cannot be milled
• Is the product shape going to change between batches
• How much finish variation is acceptable between parts
• Is thermal dissipation driving the geometry, because if it is, extrusion usually wins
• Do you have eight to ten weeks for a die, or do you need parts next month

Frequently asked questions

Keep reading

• What an Amplifier Chassis Actually Costs to Manufacture
• Specifying and Machining a Heatsink Extrusion for an Amplifier
• Getting a 19 Inch Rack Panel Right the First Time

This guide is part of Audio Chassis Manufacturing: The Whole Picture, one of four sections in the guide library.