The most common CNC part we make, and the one where the gap between a good design and a cheap design is widest. Wall thickness, pocket depth, sealing grooves and anodize allowance decide most of the price before anyone quotes it.
The same part can be produced several ways, and the choice is decided by volume and geometry rather than preference. We quote whichever is actually cheaper for your quantity.
| Approach | How it works | Best at | Watch out for |
|---|---|---|---|
| Machined from solid | One block of 6061 plate, all features cut from it | 1–500 pieces; features on multiple faces; designs still changing | Material utilisation of 15–35% — most of the block becomes chips |
| Extrusion + end plates | Constant-section body cut to length, machined end plates fastened on | 500+ pieces with a constant cross-section | Die cost ($1,500–4,000); no features on the long faces without secondary operations |
| Machined + welded | Plate walls welded into a box, then machined | Large enclosures that would need a huge block | Weld distortion; needs stress relief and a finishing pass |
These are the decisions that account for most of the cost difference between two parts of the same overall size.
| Feature | Recommended | Why it matters |
|---|---|---|
| Wall thickness | 1.0–1.2mm routine; 0.8mm with care | Below 0.8mm, deflection and handling dominate |
| Internal corner radius | ≥ 0.5× cutter diameter (min 1mm) | Sharp corners need EDM or hand work |
| Pocket depth | ≤ 4× tool diameter | Deeper needs long-reach tooling — slower and prone to chatter |
| Dimensional tolerance | ±0.1mm general; ±0.02mm on mating faces | Tightening everything multiplies inspection cost |
| Thread depth | 2× diameter through, 1.5–2× blind | Deeper threads add risk without adding strength |
| Sealing groove corner | Radiused, matched to the O-ring spec | Sharp corners force a second operation |
| Anodize allowance | 0.01–0.015mm per surface growth | Matters on threads and press fits |
Thin walls are the most common cause of an enclosure that quotes far above budget. A 1mm wall is achievable, but it has to be machined with light passes on a well-supported workpiece, and it deflects during handling and anodizing. On a 200mm tall enclosure, going from 1.5mm to 1.0mm walls can add 25–40% to the machining cost — not because the material removal is harder, but because every pass has to be gentler and the part has to be supported differently.
If the design calls for thin walls, specify 6061-T651 rather than T6. Stress-relieved plate moves far less when the pocket is cut, which is what keeps the walls straight.
| Cost element | Share of price | What to change if it is too high |
|---|---|---|
| Material utilisation | 15–35% typical for a hollow enclosure | Most of the block becomes chips — the single biggest cost lever |
| Cycle time | 40–70% of part cost at volume | Pocketing dominates; shallow wide pockets machine faster than deep narrow ones |
| Setups | 2–4 typically | Features on 4+ faces mean more setups or a 5-axis machine |
| Finishing | 10–20% | Anodizing, masking and colour control |
| Inspection | 3–8% | Critical for sealing faces and mating interfaces |
A 200 × 150 × 80mm enclosure machined from solid starts as a block weighing roughly 6.5kg and finishes around 1.2kg. You are paying for 6.5kg of aluminum and turning 80% of it into chips. That is normal for this part type, but it is worth knowing: shrinking the overall envelope, reducing wall sections where they are not structural, or switching to extrusion at volume all attack the same cost.
The counter-intuitive part: making the part smaller is often cheaper than making it thinner. Removing 20mm from one dimension saves more material than thinning four walls.
Colour varies with alloy lot, bath chemistry and rack position — not with the machining. For a cosmetic batch, material is bought for the full run at once and the anodizing lot kept together. Bead blasting before anodizing gives a uniform matte that hides tool marks far more cheaply than machining to a fine finish.
Specify a rectangular groove with a radiused internal corner and tolerance the depth rather than the width — depth controls O-ring compression. Mask the groove from anodize unless the specification says otherwise, because the coating changes the groove dimensions by roughly 0.01–0.015mm per surface.
Anodize is an electrical insulator, which is exactly wrong for an EMI enclosure. The usual answer is chromate conversion (Alodine) on the whole part, or anodize with masking on the mating and grounding surfaces. Decide this before the drawing is released — it changes the finish specification, not just the process.
Anodize grows the surface by 0.01–0.015mm per face, which is enough to make a masked thread tight and a press fit loose. Threads are normally masked; press-fit bores are either masked or pre-adjusted. Tell us which fits are critical and we will build the allowance into the machining.
For a 6061 enclosure up to about 150mm tall, 1.0–1.2mm walls are routine and 0.8mm is achievable with care. Below that, deflection during machining and handling becomes the limiting factor rather than the cutter. Thin walls also amplify any internal stress in the plate, so specify 6061-T651 for thin-wall enclosures and expect a finishing pass after stress relief.
Usually yes per part at low volume, and the crossover depends on geometry. Extrusion needs a die (typically $1,500–4,000) plus cut-to-length end plates, which wins above roughly 500–1,000 pieces for a constant cross-section. Machining from solid wins for low-to-mid volume, for enclosures with features on multiple faces, and whenever the design may still change — there is no tooling to scrap.
Three things: the same alloy lot, the same anodizer and the same rack configuration. 6061 anodizes consistently, but colour varies with silicon content between lots, with bath chemistry, and with how parts are racked. For cosmetic batches we buy material for the full run at once and keep the anodizing lot together rather than splitting the order across weeks.
Yes, and it is one of the features that most benefits from being designed for machining. A rectangular groove with a radiused internal corner is straightforward; a sharp-cornered groove needs a slotting or EDM operation. Specify the groove width, depth and corner radius against the O-ring datasheet, and tolerance the depth rather than the width — depth controls compression.
For a visible anodized enclosure, bead blasting before anodizing gives a uniform matte surface that hides tool marks and costs less than machining to a fine finish. For RF or EMI applications, chromate conversion (Alodine) plus masking of contact surfaces is more appropriate than anodizing, because anodize is an insulator.
Include the quantity, whether the finish is visible, and which fits or seals are critical. You get a line-item quote within 24 hours and DFM notes on the features driving your price.