A servo-valve spool doesn’t seal by touching the sleeve bore — it seals by running close enough that the fluid film between them is thin enough to throttle flow. That only works if the spool is round to a couple of microns all along its length, not just at the diameter a caliper happens to check. We verify cylindricity on the CMM as a distinct callout from diameter, because a part can be dead-on diameter at every station measured and still be lobed.
Part
Valve Spool
A hydraulic servo-valve spool: the land diameters seal against the sleeve bore on a fluid film a few microns thick, so cylindricity matters as much as diameter.
Part
Valve Spool
Rev
Rev C
Year
2025
Material
17-4PH stainless, H900
Tightest tolerance
±0.003mm (3 µm) diameter, cylindricity 0.002mm
Lot
60-off, running lot
Lead time
26 days
Route sheet
How this part actually got made.
| Op | Stage | Machine | Tool | Result |
|---|---|---|---|---|
| 01 | Stock | Material stores | — | Saw-cut billet, certificate matched to the traveler. |
| 02 | Turn | Okuma LB3000, 2-axis CNC lathe | CNMG 432 insert, 0.4mm nose radius | Ra ≈ 1.13 µm |
| 03 | Grind | Studer S31, cylindrical grinder | Ø8mm ball-form CBN wheel | Rz ≈ 2.81 µm |
| 04 | Inspect | Zeiss Contura CMM | — | First-article report against the drawing's GD&T callouts. |
Finish
Specified surface finish.
What the drawing calls out — verified on receipt with a profilometer, not assumed from the tool that made it.
Ra0.20 µm