Gem Modeling with GemCad
Free
About 30 minutes
GemCad installed and one design file to open
GemCad is the design software the amateur faceting community has used for decades to plan a facet pattern before ever touching a lap. A design file tells you every facet’s angle and index position in advance, and lets you preview the stone in 3D. This page walks through modeling a design yourself, even if you have never opened the software before.
What you’re looking at
A wireframe or shaded model of the stone that you can rotate freely to inspect the crown, pavilion, and girdle from any angle.
A table listing every facet with its angle and index position, this is the exact information you bring to the faceting machine.
Shows which index gear the design was built for, such as 64, 96, or 120, this must match or be compatible with your own machine.
Resizes the whole design to match the girdle diameter your rough stone can actually produce.
Step by step: modeling your first stone
Start from an existing, tested design rather than building one from scratch. Choose one whose overall proportions roughly match your stone.
Review every facet’s angle and index. Note the index gear the design requires, and confirm your machine supports it.
Check the model from the top, side, and bottom. Look for anything that seems visually off before you commit to cutting.
Adjust the girdle diameter to fit the clean area of your rough stone, checking the pavilion depth still leaves enough material.
Check the steepest and shallowest angles in the list against what your machine’s cheater and mast can actually reach.
Bring a printed or saved copy of the finished angle and index list to your bench, so you are cutting from a checked reference, not memory.
Common early mistakes
Cutting a design at its original size without checking it against your actual rough is one of the most common ways to run out of material mid-cut.
A design calculated for one refractive index will not look its best cut in a very different material. Check what the design was built for before using it.
Put a design into practice
Ready to model your own stone?
Open a template, check the facet list, and scale it to your rough before you ever touch a lap.
Browse Design Templates →