CAD software handles conversions internally, but understanding best practices prevents errors when exporting to manufacturing, collaborating internationally, or maintaining legacy designs.
1. Set Master Units at Project Start
Choose metric or imperial as your master units before modeling. Switching mid-project can introduce rounding errors in constraints and dimensions. Document your choice in project specifications.
2. Use Exact Conversion Values
CAD software stores dimensions with high precision, but displays may round. When manually converting (e.g., importing DXF files), use exact values: 25.4mm per inch, not approximate values.
3. Verify Tolerance Stack-Up
When converting assemblies, verify that tolerance stack-ups remain valid. A chain of Β±0.1mm tolerances may convert differently when looking at cumulative effects.
4. Standardize on One System per Drawing
Never mix metric and imperial dimensions on a single drawing. If you must show both (rare), clearly designate primary and secondary units.
5. Use Standard Stock Sizes
When converting designs, adapt to available stock materials. A 25.4mm shaft (converted from 1") may not be available β use 25mm (metric standard size) instead and adjust tolerances accordingly.