How to Machine Rectangular Bores for Shank-Type Ejector Blades
Key Takeaway: Rectangular shank bores require wire-EDM or sinker-EDM machining. Key specs: H7 tolerance on width/thickness, corner radii R0.1–R0.3mm (EDM cannot produce sharp internal corners), surface finish Ra ≤ 1.6μm.
Bore Preparation Procedure
- Layout: Mark bore center and orientation on the plate. Verify orientation matches the blade ejection direction.
- Pilot hole: Drill a clearance hole through the plate for the EDM wire (wire-EDM) or roughing (sinker-EDM).
- EDM machining: Program the rectangular profile with corner radii R0.1–R0.3mm. Machine to H7 tolerance on width and thickness.
- Surface finish: Verify Ra ≤ 1.6μm on all four bore walls. Polish if necessary.
- Test fit: Insert the blade and verify smooth sliding with no binding. Check orientation alignment.
Wire-EDM vs Sinker-EDM
| Parameter | Wire-EDM | Sinker-EDM |
|---|---|---|
| Precision | ±0.005mm | ±0.01mm |
| Corner radii | R0.1mm (wire diameter) | R0.2–0.3mm (electrode wear) |
| Surface finish | Ra 0.8–1.6μm | Ra 1.6–3.2μm (may need polishing) |
| Time per bore | 30–40 min | 40–50 min |