Guide Pin & Interlock Clearance Calculator
Per-side clearance for guide pins, guides and interlocks caused by the thermal expansion difference between cavity and core.
Inputs
Shows the per-side clearance. Enter the long-side and short-side spacing separately.
Results
Unrounded values
How this calculator works
When the cavity and core run at different temperatures, or are made of different metals, they grow by different amounts. Guide pins, guide blocks and interlocks need enough clearance to stay free at operating temperature without losing alignment.
This calculator returns the per-side clearance from the guide spacing and the cavity and core materials, using fixed temperature terms of 85 for the cavity and 45 for the core.
Formulas
- Per-side clearance
[spacing / 2 × (1 + cavity coefficient × 85)] − [spacing / 2 × (1 + core coefficient × 45)]- Expansion coefficients
Aluminium 0.000023; Steel 0.000012
The temperature terms are fixed at 85 (cavity) and 45 (core) and are independent of the shrinkage calculator. A negative result is kept as-is.
Worked example
Guide pins 1000 mm apart, aluminium cavity, steel core:
| Guide pin / interlock spacing | 1000 mm |
|---|---|
| Cavity material | Aluminium |
| Core material | Steel |
| Per-side clearance | 0.7 mm |
|---|---|
| Cavity expansion coefficient | 0.000023 /°C |
| Core expansion coefficient | 0.000012 /°C |
When to use it
- Setting guide pin and interlock fits on aluminium or steel molds
- Checking alignment features when cavity and core materials differ
Frequently asked questions
How is the guide pin clearance calculated?
Per-side clearance = spacing ÷ 2 × (1 + cavity coefficient × 85) − spacing ÷ 2 × (1 + core coefficient × 45). For 1000 mm spacing with an aluminium cavity and steel core, that is about 0.71 mm per side.
Why can the result be negative?
If the cavity expands less than the core, for example a steel cavity with an aluminium core, the formula returns a negative value. Check the fit direction for that combination.
Do I calculate both sides of the mold?
Yes. Enter the long-side spacing and the short-side spacing separately; each gives its own clearance.
Related calculators
Results are estimates from empirical rules used in PDCPD mold development. Verify critical dimensions before cutting metal.