Cuttable pattern rules: what gets checked and why

Most stained glass pattern generators, especially AI image tools, produce a picture that looks like a stained glass panel without checking whether any of its shapes can actually be cut in glass. Every pattern on this site is checked against three specific geometric rules, computed from the pattern's real vector coordinates at the size you choose, before it is published.

Minimum piece width: 3/8 in

A piece narrower than about 3/8 in at its narrowest point has very little glass left once the edge is ground down, and tends to snap under grinding pressure rather than survive to become part of the panel. This is computed as the shortest side of each piece's minimum bounding rectangle, not just its widest measurement.

Minimum interior angle: 30 degrees

A sharp point under about 30 degrees is difficult to grind cleanly: the grinder wheel tends to round it off or chip the tip rather than hold the exact angle. Every interior angle of every piece on every pattern is computed and checked against this floor.

Minimum reentrant curve radius: 1/4 in

On patterns with a concave, inward-curving cut, such as Crescent Moon's inner curve or Tiffany Arch Fan's arch, a curve tighter than about 1/4 in radius is hard to grind to shape without over-grinding the surrounding piece. This check applies only to patterns with a real concave curve; straight-line patterns like Diamond Lattice have nothing to check here.

What this does and does not cover

These are geometric checks against known bench constraints, run against the pattern's actual coordinates. They confirm a piece can be cut and ground at the size shown. They do not account for the specific glass you use, since some glass is more brittle than others, and they do not replace your own cutting technique or tool condition. No pattern on this site has been physically cut and tested in glass as part of this check; the verification is geometric, not physical.

Try these checks live on the free pattern with the Pattern Sizer tool.