A bracket looks like a simple part and is usually quoted as one — until it has to locate something. The machining is straightforward; what decides whether the assembly works is where the holes are relative to each other and to the mounting face, and that is a datum question rather than a tolerance question.
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 plate | Flat bracket or plate with holes and pockets, cut from 6061 plate | Flat brackets, mounting plates, and parts with pockets or ribs | Thin plates deflect; flatness after machining needs stress-relieved stock |
| Machined from solid block (L or U shape) | The whole bracket including the vertical leg cut from one block | Rigid brackets where the corner must be strong and square | Material utilisation drops sharply as the leg gets taller |
| Extrusion + machining | Standard angle or channel extrusion cut to length, holes added | Simple L or U brackets at volume with constant section | Limited to standard sections; corner radius is fixed by the profile |
| Folded sheet + machining | Sheet metal folded, then holes and features machined | Large thin brackets where weight and cost matter more than rigidity | Fold tolerance is looser than machining; datum choice becomes critical |
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 |
|---|---|---|
| Hole position tolerance | ±0.1mm general; ±0.02mm for locating pins | Position, not diameter, is what makes an assembly fit or not |
| Hole diameter tolerance | H12 general; H7 only for press fits | A clearance hole does not need a precision diameter |
| Edge distance from hole | ≥ 1.5× hole diameter | Less and the material tears out under load |
| Corner radius (internal) | ≥ 0.5× cutter diameter | Sharp internal corners need EDM or hand finishing |
| Rib thickness | ≥ 1.5mm; 2mm preferred | Thinner ribs deflect and chatter |
| Flatness (mounting face) | 0.1mm typical; 0.05mm on mating faces | Depends on whether the bracket is a locating feature |
| Datum choice | Put datums on the first-setup face | Datums on later-machined faces accumulate stack-up error |
An L-bracket mates to two surfaces at once, which means both legs are datums and neither can be machined last. If the drawing tolerances each leg independently, the two are still not controlled relative to each other — and the error shows up as a gap or a bind at assembly, not at inspection.
The fix is to tolerance the relationship, not the features: make one leg datum A, the other datum B, and control perpendicularity between them, then position the holes to those datums. That is what a machinist can actually hold, and what an inspector can actually verify.
| Cost element | Share of price | What to change if it is too high |
|---|---|---|
| Setup count | 25–40% of part cost | Each face with features is another setup — design for one or two |
| Cycle time | 30–50% | Hole count and pocketing; small brackets are setup-dominated |
| Material | 10–20% | Plate size is set by the outline, not the finished weight |
| Deburring and finishing | 5–15% | Every machined edge needs deburring, by hand on complex parts |
| Inspection | 3–8% | Position tolerance on hole patterns is what gets measured |
A small bracket with features on three faces can spend more time being re-fixtured than being cut. That is why two brackets of the same size and the same number of holes can quote 40% apart — one is designed so all features are reachable from two setups, the other needs four.
Before optimising the geometry, ask whether every feature can be reached from one or two sides. Moving a single hole to the other face often removes an entire setup, which is worth more than any tolerance relaxation.
Anodize grows the surface by 0.01–0.015mm per face, which reduces a clearance hole slightly and a press-fit hole more. On brackets with many holes, specify which fits are critical. Threaded holes are normally masked before anodize.
Machined edges have burrs, and a burr on a mounting face is a flatness error that shows up as a gap. Specify deburring on mating faces explicitly — it is normally included, but "deburr all edges" and "deburr and chamfer mounting faces" are different instructions.
A thin plate machined from standard T6 stock will bow when material is removed. For a bracket that must sit flat, order 6061-T651 and leave a finishing pass. This matters more for long thin brackets than for compact ones.
±0.1mm is adequate for clearance holes and costs nothing extra. Use ±0.02mm only for locating pins or dowels where position controls assembly alignment. Holding ±0.02mm on every hole multiplies inspection time without improving anything — position tolerance should follow function, not habit.
Because the two legs are not controlled relative to each other. If each leg is toleranced independently, the perpendicularity between them is uncontrolled, and the assembly sees a gap or a bind. Make one leg a datum, control perpendicularity to it, and position the holes from that datum.
Extrusion wins at volume for simple constant-section L and U brackets, because the profile does the forming and only the holes and ends are machined. Machining from solid wins for low volume, for non-standard geometry, and whenever the bracket has features the extrusion cannot provide. The crossover is usually a few hundred pieces.
A flat plate bracket can go to 1.5–2mm and still be machined, but it will deflect during machining and may not stay flat. Below 1.5mm, consider sheet metal with machined features instead of machining from plate. Ribs are a better way to add stiffness than thickness.
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.