About This Part
A friction disc is a torque-transmission component found in clutches, brakes and coupling assemblies. Two flat faces are pressed together under load; friction between them transfers rotational force, and any inconsistency in flatness, parallelism or surface texture causes slip, chatter or premature wear. In cnc precision disc applications the disc itself is a wearing surface, but the geometry has to be perfect every time — a disc that is slightly warped will grab, shudder or fail to disengage cleanly, and the problem usually surfaces only after the full assembly is installed and tested. This friction disc is machined from **Stainless Steel 304**, chosen for its corrosion resistance, good wear characteristics and mechanical strength across operating temperatures. The part is produced on a combination of CNC lathe and mill, with the two friction faces, central bore and any drive slots or grooves held to **±0.005 mm on critical dimensions**. Stainless steel disc turning requires a different approach than aluminum: work hardening and tool deflection are the dominant failure modes, especially on a thin, disc-shaped part where rigidity is inherently limited. Clutch plate machining demands workholding that supports the disc without distorting it, because clamping force itself can spring the part into a shape that looks perfect in the chuck and wrong when released.
**Part:** Friction Disc
**Process:** CNC turning + milling
**Material:** Stainless Steel 304
**Tolerance:** ±0.005 mm on critical dimensions
**Inspection:** 100% CMM verification, full report with shipment
Challenges of This Part & How We Machined It
Face parallelism on a thin disc
A friction disc is, by design, a thin, flat disc. When you clamp it in a chuck and apply cutting pressure, the disc flexes away from the tool — and then springs back when released, leaving a face that is not parallel to the opposite side. If the two friction faces are not parallel within a tight band, the disc contacts unevenly when clamped in service, causing hot spots, localized wear and inconsistent torque transfer. We turn both faces using a dedicated fixture that supports the disc over its full area (a face plate or backing fixture rather than a three-jaw grip at the OD), and we interleave finish passes between sides so that neither face is left with residual deflection from the other side's cut.
Work hardening of Stainless 304
Stainless Steel 304 work-hardens rapidly when a tool rubs instead of cuts. A dull insert, too-light a finish pass, or a tool that dwells leaves a hardened surface layer that the next tool cannot cut cleanly — it either deflects or wears prematurely, and in the worst case it glazes the surface so thoroughly that subsequent passes skate across without cutting. We use sharp inserts with the correct geometry for stainless, keep cutting loads consistent, avoid dwelling on finished surfaces, and take a deliberate finishing pass at a depth of cut large enough to get under any work-hardened layer from the previous pass. The result is a consistent surface texture across the entire friction face with no glazed or hardened patches.
Drive-slot geometry and concentricity to bore
Clutch plate machining commonly involves drive slots, keyways or tooth profiles around the disc OD or ID. These features must be concentric to the central bore or the disc will run eccentrically when installed on a shaft, causing cyclic loading on the friction material and premature failure. We mill or broach drive features in a setup that references the bore as the primary datum, not the chucked OD, so that slot-to-bore concentricity is maintained even if the OD has minor runout from the turning operation. Feature positions and bore diameter are verified on the CMM.
Machining Sequence
1. **CAM programming and tool selection** — insert geometry and cutting parameters are selected specifically for Stainless 304 to avoid work hardening, with a facing strategy designed around full-disc workholding rather than perimeter clamping.
2. **Turning of OD, bore and first face** — the blank is turned to rough profile, then both friction faces are finished in alternating light passes on a face-drive or backing-plate fixture.
3. **Milling of drive slots/features** — slots or keyways are milled on a mill with the part located off the finished bore to preserve concentricity.
4. **Deburring and edge prep** — sharp edges around slots and OD are broken consistently; friction faces are protected from scratches through final packaging to avoid damage that would create high spots.
5. **CMM inspection** — face parallelism, bore diameter, slot positions, and surface finish are verified; CMM report ships with the parts.
What You Get With Every Order
- **Free DFM review before quoting** — we flag manufacturability risk early, not after parts are made - **First Article Inspection report** with the first batch - **CMM dimensional report** on critical features - **Material certificates** for aerospace and medical grades - **Direct communication with the shop** — no trading company in between, we make the parts ourselves
Have a Drawing?
Send us your drawing or STEP file and we will come back with pricing within 48 hours. Prototype quantities and production runs both welcome — no minimum order quantity.
**TruPart Precision** trupartprecision.com | sales@trupartprecision.com WhatsApp: +86 137 1278 3205 No.114 Xinhua Road, Xinhe Dev Zone, Wanjiang, Dongguan, China