UAV Radiation Detector Brackets CNC

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  What the bracket actually controls
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  Where 3-axis machining stops working
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  Material choice and what it does to the part
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  Finish, shielding and the small details
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  Inspection: proving the bracket before it flies
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  Machining route by bracket geometry

A radiation detector on a UAV is a mass at the end of a lever. Every gram of bracket sits far from the airframe's center of gravity, so bracket mass shows up twice: once as payload weight, once as a trim problem. Most detector heads used on small airframes weigh between 0.3 kg and 2 kg, which means a 150 g bracket is not a rounding error.

The second job is angular. Scintillation crystals and solid-state detectors are directional: count rate falls off as the source moves off the crystal axis. If the bracket tilts the detector 1° from the intended axis during a 40 m survey pass, the ground footprint shifts and the count map smears. Tight angular tolerance is not cosmetic here. It is the difference between a usable map and a set of numbers nobody trusts.

The third job is stiffness. A bracket that flexes under rotor vibration changes the detector's pointing angle at the same frequency as the blades. That modulation appears in the count data as noise you cannot filter out afterward, because you no longer know where the detector was looking.

So the drawing usually carries three numbers that matter more than the rest: mass budget, angular position of the detector mounting face, and flatness of the face that seats the detector. Everything else on the part is secondary.

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  Mass budgetOften 80–200 g for a small detector head.
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  Angular positionTilt of the detector face sets where the count map lands.
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  StiffnessFirst mode should sit well above rotor and gimbal frequencies.
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  Seat flatnessA rocking detector face injects pointing error directly.

A detector bracket is rarely a flat plate with holes. Typical geometry includes a canted detector face, two or more mounting bosses at different angles, a cable channel that runs around a bend, and pockets cut into the arms to pull mass out. That is four features on five or six distinct faces.

On a 3-axis mill you reach each face by re-fixturing. Every re-clamp adds an error stack: vise repeatability, chip under a locating pin, a soft jaw that was cut yesterday. In practice a four-setup part drifts by 0.05–0.1 mm between features, and the angular relationship between the detector face and the airframe mounting holes drifts with it.

Five-axis machining holds the part in one clamping and rotates the tool around it. The angular relationships are cut into the part while it never moves, so the error stack collapses to the machine's own geometry. On our 16 simultaneous 5-axis centers that shows up as feature-to-feature position inside ±0.005 mm on a well-prepared blank.

There is a second benefit that is easy to miss. Sculpted arms and blended fillets need the tool to approach from an angle a 3-axis spindle cannot reach. Ball-end milling with the tool tilted keeps chip load even across a curved surface, so the scallop height stays consistent instead of blowing out at the ends of the pass.

That matters on a part that sees airflow. A rough blend on a bracket arm is a stress riser and a place where a burr will abrade a cable jacket over a hundred flights. A smooth, predictable surface is a maintenance item you never have to think about.

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  One clamping on 5-axisFeature-to-feature error drops to machine geometry.
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  Tilted ball-end millingEven chip load across a contoured arm.
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  Fewer setupsLess handling, fewer chances for a dinged mounting face.

Most UAV detector brackets are cut from aluminium, and the two workhorses are 6061-T6 and 7075. 6061-T6 machines cleanly, takes anodizing evenly, and is forgiving on thin walls. 7075 gives roughly 60% more yield strength at similar density, which lets you cut the arm sections thinner for the same stiffness. It costs more and it is less friendly to anodize for corrosion, so it usually appears on brackets where mass really is the constraint.

Where the airframe sees salt spray or decontamination wash-down, 316L stainless and 17-4PH come into play. Both are heavier for the same stiffness, so they appear as small fittings rather than whole brackets. Titanium TC4 (Ti-6Al-4V) sits between them on mass and is used when the bracket also has to survive heat near a power module.

Magnesium AZ31B and AZ91D are the lightest option and are used on some airframes. The trade is corrosion control: magnesium needs a coating that survives handling, and any bare edge becomes a corrosion site. We machine it, but we ask what the wash-down procedure looks like before quoting it.

The material also sets the wall you can hold. A 1.5 mm aluminium wall is routine. A 1.5 mm magnesium wall with a 40 mm unsupported span will ring. On thin sections we usually leave a machined rib rather than push the wall thinner, because the rib costs less mass than the extra wall thickness it replaces.

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  6061-T6General-purpose, good anodizing, forgiving on thin walls.
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  7075Higher strength, thinner arms, harder to anodize for corrosion.
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  316L / 17-4PHSalt spray and wash-down service, heavier per unit stiffness.
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  Magnesium AZ31BLightest route, needs a coating that survives handling.

Anodizing is the default finish on aluminium brackets. Type II clear or black gives corrosion protection and a hard, non-conductive surface. If the bracket is part of a grounding path, we mask the contact pads or use conductive anodizing so the joint is not insulated by its own coating.

Hardcoat anodizing is worth the cost on parts that get handled every flight, because the coating resists the scratches that come from repeated install and removal. On magnesium, a chemical conversion coat followed by powder coat holds up better than anodizing alone.

Electroless nickel is common on stainless and steel fittings where wear resistance matters more than color. Bead blasting before coating gives a matte, uniform look and hides tool marks on cosmetic faces, though it also slightly changes the surface roughness reading.

One detail that gets forgotten: laser marking. Serial numbers, torque values and orientation arrows are marked directly on the bracket at a minimum character height of 1.5 mm, so a technician in the field can read the torque spec without a drawing. It is a small thing that prevents a large mistake.

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  Masking for groundingConductive anodizing or masked pads keep the joint bonded.
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  Hardcoat on handled partsResists scratches from repeated install cycles.
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  Laser markingTorque values and orientation arrows at ≥1.5 mm character height.

A machined bracket is only as good as the evidence that it matches the drawing. For detector brackets, three checks carry most of the risk: the angle of the detector mounting face, the position of the airframe mounting holes relative to that face, and the flatness of the seat.

We check the first two with a coordinate measuring machine against the datum scheme on the drawing. Seat flatness gets a surface check plus a light-blue fit test on a granite plate when the drawing calls for it. Reports are available on request, and 100% inspection happens before shipment: raw material check, in-process monitoring, final inspection.

Surface roughness is specified where it matters. A detector seat usually wants Ra 0.8–1.6 μm so the detector sits without rocking. Non-critical outer faces are fine at Ra 1.6–3.2 μm as machined. Only sealing faces or optical seats justify Ra 0.2–0.8 μm, and they cost more because they need a separate finishing pass.

For anyone building a first article, our sample center runs the part through the same inspection path as production, so the report you see at prototype stage is the same format you get at volume.

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  CMM on anglesDetector face angle and hole position to datum.
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  Seat flatnessSurface check plus fit test when specified.
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  Roughness by functionRa 0.8–1.6 μm on seats, as-machined elsewhere.