- 5 axis
- A machine that can tilt and rotate the part as well as move in three directions, so faces that are square to each other can be cut without releasing the part. On UAV work it is bought for that squareness, not for sculpted shapes.
- Anodise, type II
- A sulphuric acid oxide layer roughly 5 to 25 micrometres thick. Takes dye well, protects moderately, changes dimensions very little.
- Anodise, type III, hard anodise
- A thicker and harder oxide, roughly 25 to 75 micrometres. Wear and corrosion resistant, dark, and thick enough that it changes fits.
- AQL
- Acceptable quality level. The sampling standard that says how many parts out of a lot get inspected and how many defects allow the lot to pass.
- Bolt circle
- The pitch circle a set of fastener holes sits on, for example a motor mount pattern. What matters is the position of the holes relative to each other, not the diameter of the circle.
- Boom
- The tube that carries a motor away from the body of a multirotor, usually carbon fibre, clamped at both ends by machined fittings.
- Burr
- The raised edge left where a cutter exits the material. Burrs cut fingers, hold anodise badly and sit on datum faces where they corrupt measurement.
- Chamfer
- An angled break on an edge. Cheap, and it guides fasteners and mating parts into place.
- CMM
- Coordinate measuring machine. A probe on a precise frame that measures where features actually are, which is how position, form and orientation get reported.
- Concession
- A request to accept a part that deviates from the drawing. The decision belongs to the buyer, not the shop, and it should always come with the measured deviation.
- CTE
- Coefficient of thermal expansion. How much a material grows per degree. Polymers move several times more than aluminium, which is why close plastic to metal fits need a stated temperature.
- Datum
- The reference a measurement is taken from. Change the datum scheme and every number on an inspection report changes, which is why two labs sometimes disagree about the same part.
- DFM
- Design for manufacture. In practice, the questions a shop asks before quoting: corner radii, pocket depth, wall thickness, how the part will be held.
- EXW
- Ex works. The buyer takes the goods at the seller dock and pays for everything after that. Quotes here are EXW unless stated otherwise.
- FAI
- First article inspection. One part measured completely against the drawing before the lot runs, so mistakes cost one part rather than five hundred.
- Fixture
- Dedicated work holding built for one part. Costs money once, then buys repeatability and shorter cycle times on every part after that.
- Galvanic corrosion
- Corrosion driven by two different materials in electrical contact with an electrolyte between them. Aluminium against carbon fibre is the version that eats UAV clamps.
- GD&T
- Geometric dimensioning and tolerancing. The symbol language for position, form and orientation, which describes what a part has to do rather than only how big it is.
- Gland fill
- The proportion of an o-ring groove that the compressed seal occupies. Too low and the seal moves, too high and it has nowhere to go when it is squeezed.
- H7
- A hole tolerance class from the ISO fit system. On a 25 mm bore it is roughly plus 0.021 mm and minus zero, which is the usual call out for a bearing seat or a located tube.
- Heat treatment
- Controlled heating and cooling that changes the strength of a metal. On aluminium it is what the T6 in 6061-T6 refers to.
- IP rating
- A two digit code for ingress protection. The first digit is dust, the second is water. IP67 means dust tight and able to survive short immersion.
- Laser marking
- Marking a part number, revision or code with a laser. Adds no weight and survives anodising if it is done in the right order.
- Lot code
- The number that ties a group of parts to the material, the work order and the inspection records. Without it, a field failure cannot be traced.
- Mill certificate
- The document from the mill that made the metal, stating chemistry and mechanical properties for a heat or lot. It says what the material is, not who machined it.
- MOQ
- Minimum order quantity. Here it is one piece for a prototype, which is unusual, and it exists because UAV programmes iterate.
- Passivation
- A chemical treatment that removes free iron from a stainless surface after machining, so the part does not show rust spots in a week.
- PPAP
- Production part approval process. A package of documents proving a process can make the part repeatedly. Level 3 is the common request.
- Ra
- Average surface roughness in micrometres. A milled aluminium face is typically Ra 1.6. Lower numbers mean smoother and, past a point, another process.
- RoHS
- A restriction on hazardous substances in materials and finishes. A declaration, not a quality certificate.
- Setup
- One orientation of the part in the machine. Every extra setup adds cost and adds error between the features cut in different setups.
- Squeeze
- How much an o-ring is compressed, as a percentage of its cord diameter. Typically 15 to 30 percent on a static face seal. Zero squeeze is a groove that does not seal.
- Stress relief
- Letting a part rest, or heat treating it, between roughing and finishing so the stress released by machining does not warp the finished shape.
- T6
- A temper designation meaning solution heat treated and artificially aged. It is why 6061-T6 is far stronger than annealed 6061.
- Tabs
- Small sections of material left to hold a part in the stock until the last cut, so it does not move or fly out while it is being machined.
- Thread engagement
- How much thread length actually carries load. In aluminium, one and a half to two screw diameters. Less than that is a thread waiting to strip.
- TIM
- Thermal interface material. Paste, pad or film between a component and a heat sink. Thinner is better, and a pad taking up a big gap is a design problem.
- True position
- How far a feature centre is from where the drawing puts it, in any direction, reported as a diameter. One number instead of two, and it matches how a bolt actually fits.
- Wire EDM
- Cutting with an electrically charged wire. Reaches sharp internal corners a cutter cannot, and cuts hardened material without heat damage.
- Work holding
- How a part is gripped while it is cut. On thin UAV plates it decides flatness more than any tolerance on the drawing does.
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