CNC milling: 3, 4 and 5-axis parts to ±0.05 mm
Billet and plate up to 1000 × 600 × 400 mm, with the fixture designed before the toolpath. Standard tolerance ±0.05 mm, ±0.01 mm on the features that locate the assembly.
What the process holds well
A 6 mm end mill reaches about 24 mm before chatter and deflection start eating the tolerance. Beyond that the quote either adds a long-reach tool at reduced feed, or opens the corner radius so a larger cutter fits.
Reached by roughing, stress-relieving and finishing in that order on thin aluminium. Skip the stress relief and the plate bows once the clamps come off, however good the finishing pass was.
Better when holes are bored rather than interpolated, and better again when they are machined in the same setup as the datum face they are checked from.
Small-stepover finishing passes reach Ra 0.8 µm on aluminium; Ra 0.2–0.4 µm comes from grinding, lapping or polishing as a separate operation. Sealing faces usually need that second operation.
Tolerance by feature, and what it costs
| Feature | Standard | High precision | Cost impact |
|---|---|---|---|
| General dimensions | ±0.05 mm | ±0.02 mm | Low |
| Mating bores | ±0.02 mm | ±0.01 mm | Medium, requires boring |
| Bearing seats | ±0.02 mm | ±0.01 mm | High, fine bore or grind |
| Position, hole pattern | ±0.05 mm | ±0.02 mm | Medium |
| Perpendicularity | 0.03 mm | 0.01 mm | Medium |
| Parallel faces | 0.03 mm | 0.01 mm | Medium, second op or grind |
| Ra finish | Ra 1.6 µm | Ra 0.4 µm | High, extra passes |
What pushes the price up
Every re-clamp adds handling, a datum transfer and a chance of error. Moving a critical feature onto the face machined last often costs less than holding a tight tolerance across two setups.
Walls thinner than about 1 mm in aluminium need lighter radial cuts, more passes and sometimes a support fixture. Design at 1.5 mm and the price drops without losing function.
The corner radius sets the smallest cutter that can reach it, and the cutter sets the feed rate. A 0.5 mm corner where 3 mm would work can double the cycle time of the pocket.
Pre-hardened 4140 at 30 HRC mills fine. At 50 HRC the same part needs carbide grades, lighter cuts and often a grinding allowance, and the quote reflects it.
Questions we get on this process
Yes. Plate is cheaper per kilo and closer to finished thickness, so on flat parts above 10 mm the quote usually starts from plate and faces it flat rather than cutting down a block.
Yes, on request or when the drawing implies it. The report covers bores, positions, flatness and any GD&T frame, measured on a CMM using the datum scheme from the drawing.
1000 × 600 × 400 mm inside the machine envelope, less when a fixture and clamping take up space. Longer parts are possible by repositioning, which adds a setup and a datum transfer to the price.
Hand deburr on handled edges, vibratory finishing on batches where every edge matters, and a specified edge break where the drawing calls it out. It is part of the process, not a separate line item.
Send the model and we will tell you which faces cost the money.
The quote states the setup count we assume, so you can see whether a design change would drop the price before committing to tooling.
From the shop notes
Longer answers to the questions these pages raise.