Projector sewing: cutting fabric from a projected pattern

Projector sewing means projecting a pattern at actual size onto fabric laid on your cutting table, then cutting or marking directly along the projected lines, with no printing, trimming or taping. You need a projector mounted above the table and pointing straight down, a laptop or tablet to display the file, and a calibration so that 5 cm on the file measures exactly 5 cm on the table. Once it is set up, you go from a pattern file to cut fabric in minutes.

What you need

• A projector. A native resolution of 1920 × 1080 (1080p) gives crisp, thin lines; lower resolutions work, with thicker lines. Brightness matters less than you might think in a dimmed room.
• A mount. A ceiling mount, a wall arm, a sturdy shelf or a tall boom stand, so that the lens sits above the middle of the table and points straight down.
• A cutting surface. A table at a comfortable height, covered with a self-healing cutting mat; a printed grid on the mat helps you check the scale.
• A laptop or tablet with a PDF viewer that lets you type an exact zoom percentage, or a projector app with calibration, panning and rotation.
• A projector file of your pattern: one large page at actual size, with no tiles.
• Cutting and marking tools: a rotary cutter or shears, tailor's chalk, pattern weights and a long ruler.

How big will the projected area be?

A projector's throw ratio is the distance to the surface divided by the width of the image, so the image width equals the distance divided by the throw ratio. A projector with a throw ratio of 1.2 mounted 1.5 m (5 ft) above the table gives an image about 1.25 m (49 in) wide; a short-throw projector with a ratio of 0.5 gives the same width from about 62 cm (24 in).

A bigger image covers more fabric at once, but it is dimmer and each pixel is larger: 1920 pixels across 1.25 m are about 0.65 mm each, so a line two pixels thick is about 1.3 mm wide. An image about the size of a large cutting mat is a good compromise; for bigger pieces, you pan the file across the table.

Set up the projector

1. Mount the projector above the center of the table with the lens parallel to the tabletop. Check with a spirit level, or a level app on your phone, placed on the projector body.
2. Set any keystone correction to zero. Digital keystone squeezes the image unevenly, which distorts the scale; correct the angle of the projector physically instead.
3. Connect the laptop, mirror or extend the display, and set the output to the projector's native resolution. Turn off any zoom, overscan or "fit" mode on the projector.
4. Focus on the table surface, then dim the room.

Calibrate the scale

1. Open the projector file and find the test square, or any line whose exact length you know.
2. Measure the projected square with a rigid ruler laid on the mat.
3. Change the zoom percentage until the square measures exactly 5 cm (or 2 in) in both directions.
4. Pan the square to each corner of the projected area and measure again. If it grows toward one side, the projector is not level: adjust the projector, not the zoom.
5. Check a longer distance as well: measure across a large piece on the table and compare it with the same distance measured with your PDF viewer's measuring tool, or line up a projector app's calibration grid with the grid on your mat.
6. Write down the zoom percentage. As long as the projector, table and display settings stay the same, you can reuse it, but check the test square at the start of every session anyway.

Cut the fabric from the projection

1. Press the fabric and lay it out as the cutting layout shows, usually folded in half lengthwise, selvage to selvage, right sides together.
2. Rotate the file so that each grainline arrow runs parallel to the selvage. Measure from both ends of the arrow to the selvage; the two distances must match.
3. For pieces marked "place on fold", line up the fold edge of the piece with the fold of the fabric.
4. Hold the fabric flat with weights so the layers cannot shift.
5. While the pattern is projected, mark notches, dots and dart points with chalk.
6. Cut along the solid cutting line. Your hands cast shadows, so cut from the side, or trace the whole outline with chalk first, switch the projector off and cut along the chalk.
7. Pan to the next piece without changing the zoom, and repeat. Rectangles given as cutting dimensions are measured straight onto the fabric with a ruler.

Tips for dark and printed fabrics

• Invert the colors in your viewer or app so the lines are white on black: the fabric is lit only where the lines are, and they stand out much better.
• Increase the line thickness if your app allows it.
• Darken the room further, and mark with light chalk on dark fabric.

Projector files from Sewly

On paid plans, Sewly can produce a projector file instead of tiled pages: one page at actual size, with the pieces packed into a strip no wider than 140 cm (55 in) so they map onto common fabric widths, and a 2 cm (3/4 in) margin. Large plain rectangles are given as cutting dimensions. Pair the file with the cutting layout in the sewing guide, and see laying out and cutting fabric on grain for how pieces are placed.

Common mistakes

Projector sewing is not the only way to avoid taping pages: a copy shop can print the whole pattern on large sheets, and how to print a PDF sewing pattern covers home printers. For equipment choices, read setting up a projector for sewing on a budget.