LocatingBeta

3-2-1 Locating and Pin Layout Card

Printable engineering card for 3-2-1 referencing, fixed/floating pin strategy, and datum validation.

Inputs

Part envelope L [mm]Part envelope W [mm]Part envelope H [mm]Part mass [kg]Primary datum (3 points)Secondary datum (2 points)Tertiary datum (1 point)Pin diameter selection [mm]Material pair (for notes)Apply thermal expansion allowance

Temperature delta ΔT [°C]

Results

Recommended minimum edge distance for pins15.0 - 20.0 mm (1.5-2.0 x Ø10)

1 fixed + 1 floating pin strategyFixed + Floating: Round + Slot

H7/h6 fit guidance

Use reamed H7 hole with h6 pin for fixed location. On floating side, use slot/elongated hole for assembly and thermal tolerance.

Thermal expansion note

Estimated part thermal growth on long axis: 0.138 mm

Part-fixture differential growth: 0.072 mm

Floating pin slot extra clearance suggestion: 0.172 mm

Mass note4.20 kg - verify contact area to avoid local crushing.

Pin Plan Table

Feature	Fixed/Floating	Hole type	Notes
-	Fixed	Round	-
-	Floating	Slot	-

Checklist

Operator accessibility and loading direction are clearChip evacuation and debris pockets are availableChamfers/lead-ins exist at pin entry pointsAnti-rotation stop or side support is definedDatum surfaces are clean and rigid for repeatabilityInspection access is available for critical datums

Completed items: 0/6

Notes Table

References

ISO 286: Hole/shaft fit guidance (H7/h6 usage).
3-2-1 principle: practical way to constrain 6 degrees of freedom.
Dimension the fixed pin-datum relation explicitly in manufacturing drawings.
Use floating pin + slot where thermal growth can create binding.

Disclaimer

Typical guidance, verify with standards and responsible engineer.