Machining is where most space and aerospace hardware starts: brackets, fittings, housings, struts and MGSE interfaces, in alloys that are unforgiving for a manufacturer without prior experience in them. We execute machined parts through partners qualified on those alloys, hold the drawing revision on their behalf, and inspect to the level the drawing calls. We state what will drive cost before you commit, not after.
What actually drives cost
Cycle time is rarely the driver on aerospace parts. These are:
- Setups. Every re-fixturing is a datum transfer. A part with features on five faces is cheaper on a 5-axis machine in one setup than on a 3-axis machine in four, once quantity passes a handful.
- Distortion after stress relief. Thin walls and long aspect ratios move when residual stress is released. Holding flatness on a long, thin bracket is a fixturing and sequencing problem, not a machining one, and it is priced as such.
- Tolerance class on the wrong features. ±0.025 mm on a bearing seat is normal. ±0.025 mm on a clearance hole is a CMM record nobody needs.
- Material. Titanium and nickel alloys run at a fraction of the feed of aluminium and eat tooling. The machinability factors in our lead-time model reflect that; a 7075 bracket and the same bracket in Inconel 718 are not the same job with a different price.
- Finish sequence. Anodise, chem-film and passivation each add days and each has masking implications. Threads and datum faces are usually masked; say so on the drawing.
Design guidance
- Keep walls at or above 1.2 mm where you can. Between 0.8 and 1.2 mm we will ask for a stress-relief step or an accepted flatness deviation. Below 0.8 mm the line is held for review.
- Internal corner radii: specify the largest radius the design allows. A 1 mm internal radius on a deep pocket forces a small cutter and a long cycle; 3 mm rarely changes function.
- Pocket depth to cutter diameter beyond about 4:1 invites chatter. Step the depth or open the pocket.
- Put datums where the machinist can actually locate on them, and call them on the drawing. A machined datum face on a raw casting or a plate is worth more than any tolerance note.
- Threads: call the class, the depth and whether an insert is fitted. State whether threads are masked during finishing.
- Say which finish, to which specification, on which surfaces. "Anodise" without a type and class is not a finish call-out.
Where machining is the right answer, and where it is not
Machining wins on accuracy, on repeatability across a batch, and on the alloys that nothing else handles well: titanium, 17-4 PH and nickel alloys. It loses on deep internal channels, lattices and geometry that cannot be reached by a cutter; those are additive parts with machined interfaces. It also loses on large thin panels, which are sheet-metal parts. A drawing that asks for a machined-from-solid part where a formed and machined one would do is the most common cost error we see, and we will say so at DFM.