Bore Straightness for Large-Diameter Core Pins
Key Takeaway: Large-diameter core pins (ø12mm+) require tighter straightness control because their mass makes them prone to heat-treatment sag. Specify ≤ 0.02 mm/100 mm and verify with incoming inspection — reject and replace rather than straighten.
Straightness Tolerance by Pin Diameter
| Pin Diameter | Standard Straightness | Precision Straightness |
|---|---|---|
| ø3–8 mm | ≤ 0.03 mm/100 mm | ≤ 0.01 mm/100 mm |
| ø8–12 mm | ≤ 0.025 mm/100 mm | ≤ 0.01 mm/100 mm |
| ø12–25 mm | ≤ 0.02 mm/100 mm | ≤ 0.008 mm/100 mm |
| > ø25 mm | ≤ 0.015 mm/100 mm | ≤ 0.005 mm/100 mm |
Measurement Method
- Mount pin between V-blocks on a surface plate
- Place dial indicator at pin midpoint
- Rotate 360° — record max/min readings
- TIR ÷ 2 = straightness deviation
- Measure at multiple points along length for long pins
Impact on Molded Parts
Straightness error creates a "banana" shape in the internal hole, causing wall thickness variation from one side to the other. This is especially problematic for cylindrical containers, barrels, and housings where uniform wall thickness is required for structural integrity or cosmetic appearance.
Frequently Asked Questions
What straightness tolerance for large core pins?+
≤ 0.02 mm/100 mm for ø12–25 mm. ≤ 0.015 mm/100 mm for > ø25 mm. Measured between V-blocks with dial indicator.
Why is straightness more critical for large pins?+
Large pins are heavier (gravity sag during heat treatment) and form larger features where straightness error causes proportionally larger wall thickness variation.
Can a bent pin be straightened?+
Not recommended for production. Cold straightening risks cracking; hot straightening risks hardness change. Replace bent pins.
Related
Need Large-Diameter Core Pins?
Specify diameter, length, and straightness requirement — we manufacture with verification certificate.
✓ Straightness certified✓ Sizes up to ø50 mm✓ MOQ 1 piece