Plate Preparation for Taperless Core Pins: Bore Machining & Fit Guide
Key Takeaway: Machine plate bores to H7 tolerance for taperless core pins. No taper reaming required — just straight drilling and reaming. Retain pins by head clamping between core plate and backing plate. The entire process is simpler, faster, and more forgiving than taper bore preparation.
Bore Machining Steps
- Step 1: Drill pilot hole — Drill to 0.3–0.5 mm undersize with a precision drill bit
- Step 2: Ream to H7 — Use a precision reamer to finish the bore to H7 tolerance. For ø5 mm pin: bore = 5.000 to 5.012 mm.
- Step 3: Verify bore diameter — Measure with a bore gauge at three depths (entry, mid, bottom). All readings must be within H7.
- Step 4: Machine counterbore for head — Counterbore diameter = pin head diameter + 0.05 mm clearance. Depth = pin head thickness ± 0.02 mm.
- Step 5: Deburr — Remove all burrs from bore entry and counterbore shoulder.
Bore Tolerance Table
| Pin ø (mm) | H7 Bore Tolerance | h7 Pin Tolerance | Max Clearance |
|---|---|---|---|
| ø3 | 3.000 to 3.010 | 3.000 to 2.990 | 0.020 mm |
| ø5 | 5.000 to 5.012 | 5.000 to 4.988 | 0.024 mm |
| ø8 | 8.000 to 8.015 | 8.000 to 7.985 | 0.030 mm |
| ø10 | 10.000 to 10.015 | 10.000 to 9.985 | 0.030 mm |
Retention Methods
| Method | Mechanism | Removable? | Best For |
|---|---|---|---|
| Head clamping | Pin head sandwiched between plates | Yes (disassemble plates) | Standard — most common method |
| Set screw | Screw into flat on pin shank | Yes (loosen screw) | Quick-change applications |
| Interference fit | H6/h5 tight press fit | Difficult (press required) | Permanent installations |
| Adhesive | Loctite or similar retaining compound | With heat (250°C) | Low-load applications |
Taper-to-Straight Conversion
When converting an existing taper-bore mold to taperless pins:
- The taper bore must be re-drilled to a larger straight bore (the taper exit diameter is the minimum bore achievable)
- Select the next standard taperless pin diameter that fits the enlarged bore
- Verify the part wall thickness is acceptable with the larger pin diameter
- Re-machine counterbores for the new pin head dimensions
According to ISO 286, H7/h7 is the recommended standard fit for cylindrical components requiring easy assembly with minimal clearance — exactly the application profile of taperless core pin retention.
Frequently Asked Questions
What bore tolerance is required for taperless core pins?+
H7 tolerance for standard applications. For ø5 mm pin: bore = 5.000 to 5.012 mm. This provides close-clearance fit allowing hand insertion with minimal lateral play.
How are taperless core pins retained in the plate?+
Most commonly by head clamping between core plate and backing plate. Also available: set screws (quick-change), interference fit (permanent), or adhesive (low-load).
Can I convert taper bores to straight bores?+
Yes — re-bore to the next standard straight diameter. The taperless pin will be one size larger. Verify part wall thickness is acceptable with the enlarged pin.
Taperless Core Pin Products
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