Pattern Sizer: try the cuttability checks live

Pattern Sizer runs the same checks used on every paid pattern, live, in your browser, on the free First Cut Medallion pattern. Pick a panel width between 6 in and 16 in and a cutting technique, foil or lead came, and watch the numbers update: piece count, minimum piece width, minimum interior angle, cutting margin, and glass area per color with a 15 percent waste allowance.

The checks shown here are geometric. They confirm a piece can be cut and fitted at the size shown; they do not replace checking your own glass, tools, or technique.

Every paid pattern in the catalogue runs through the same checks at build time, for the exact size you order.

What to watch while you slide the size

Three numbers move together as the panel grows or shrinks: the minimum piece width, the smallest interior angle and the tightest reentrant radius. Watch which one hits its limit first. On radial patterns it is almost always the angle at the center, where wedges converge; on banded patterns it is the width of the narrowest band. Knowing which constraint binds tells you what to change if you need a smaller panel.

Foil and came are not the same panel

Switching technique changes the margin subtracted from every piece, so the same pattern at the same width returns different numbers. Lead came takes a wider margin than copper foil because the heart of the came sits between the pieces. A pattern that is comfortable in foil at 10 in can fail in came at the same width, which is not a flaw in the pattern: it is the reason technique is chosen before the file is generated.

Using it before you buy

The sizer runs on the free First Cut Medallion, but the checks are the ones applied to every paid pattern. Run your intended panel width through it, see how close the numbers sit to their limits, and you will know how much margin for error your own cutting has before you spend anything.

Field procedure for using the numbers

Start with the outside opening, not with the visible glass size. Measure the frame rabbet or the planned border stop in 3 places, top, middle, and bottom. Use the smallest measurement as the maximum finished panel width. If the frame is not square, subtract another 1/16 in to 1/8 in before choosing a pattern size.

Set the sizer to that working width and choose the same assembly method you will use at the bench. Do not use foil numbers to plan a lead came panel. Record the minimum piece width, the smallest interior angle, and the cutting margin before changing the slider again. A paper note beside the glass is often safer than relying on memory after several size tests.

Then test 2 smaller sizes and 2 larger sizes in steps of 1/2 in. This shows how fast the tightest details change. If a 1/2 in reduction causes the narrowest feature to drop sharply, the design is near a practical limit and should not be scaled down casually.

Print or trace only after the final size is chosen. A common working tolerance for a hand cut small panel is about 1/32 in per piece edge when the cutter, grinder, and layout are all controlled. On a cluster of 10 small pieces, those small errors can add up to 1/8 in across the panel if they all drift in the same direction.

Bench equipment and working dimensions

The sizer gives geometric checks, but the bench setup controls whether those checks remain useful. A simple setup for a small medallion should include a flat board larger than the panel by at least 2 in on all sides, straight layout stops, a fine marker, pattern shears or a blade suited to the chosen method, a glass cutter, running pliers, grozing pliers, and a grinder or stone for small corrections.

Item to check	Useful figure	Why it matters
Frame allowance	1/16 in to 1/8 in smaller than the tightest opening	Prevents a finished panel from binding in an uneven frame.
Layout board margin	At least 2 in beyond the panel on each side	Leaves room for stops, pins, and checking diagonals.
Diagonal check	Difference under 1/16 in on small panels	Shows whether the setup is square before cutting begins.
Trial cut glass	One scrap strip about 1 in wide	Confirms score pressure and break behavior before using selected glass.
Pattern review time	5 to 10 minutes before cutting	Catches narrow pieces, sharp points, and repeated colors before glass is marked.

For glass thickness, do not assume that every sheet in the same project behaves the same. Opalescent, heavily textured, streaky, and flashed glass can break differently even at the same nominal thickness. If a piece has a narrow neck or a sharp inside turn, cut a similar shape from scrap before cutting the final color.

Frequent mistakes and recovery steps

The most common mistake is choosing a size from the finished visual design instead of the mounting opening. Recovery is simple if no glass has been cut: remeasure the opening, choose the smaller safe width, and regenerate or redraw the working copy. If several pieces are already cut, build the panel dry on the layout and measure the real outside size before cutting any more glass.

A second mistake is ignoring the direction of texture. Ribbed or seeded glass may score cleanly in one direction and resist a tight curve in another. When the sizer shows a small angle or a narrow piece, rotate the template on scrap first. If the break runs away from the score, change the grain direction if the design allows it, or choose a less directional glass for that piece.

A third mistake is grinding every piece until it matches the line exactly. This can make the final panel loose because the assembly gap is already part of the method. Recover by dry fitting groups of 3 to 5 pieces at a time. If a group is undersize, stop grinding adjacent pieces and let the normal foil or came space absorb the difference where possible.

If a point snaps off, recut the piece rather than filling the missing point with solder or putty.
If a narrow strip breaks twice, cut it slightly oversize first, then reduce it with the grinder in short passes.
If the center grows crowded, assemble from the tight center outward, not from the border inward.
If the border will not close, check diagonals before blaming a single piece.

Special cases that need extra margin

Small radial panels need extra attention at the center because several score lines meet within a small area. Leave the center pieces until your hand is warm and the cutter pressure is consistent. A 10 minute practice session on scrap is often enough to prevent the first real piece from becoming the test piece.

Lead came work needs a stricter dry fit than foil when many small pieces meet. The came heart occupies space between pieces, so a shape that looks acceptable as bare glass can become too large after assembly. Check each ring or band as a unit before moving to the next one.

Textured glass on tight curves is another special case. The score wheel may ride over high spots, and running pliers may start the break away from the intended line. For those pieces, keep the cutter upright, use steady pressure, and make the break in smaller stages from both ends rather than forcing one long run.

If you are comparing the live check with a catalogue pattern, remember that the paid file is checked at its ordered size. For general ordering and file questions, use the FAQ before cutting, not after the glass is on the bench.