Clamshell Quilt Template 2/3/4/6 in, Trace & Cut

Clamshell templates with the 1/4" seam allowance built in. Draw round, cut with scissors, match the notches, sew.

Files

• STL: set_default.stl (the 4" clamshell). Plain mesh, any slicer.

• 3MF: clamshell_4in_quarter_sa.3mf, clamshell_3in_quarter_sa.3mf, clamshell_2in_quarter_sa.3mf, clamshell_6in_quarter_sa.3mf. Bambu Studio project with my settings (PrusaSlicer opens the geometry).

• SCAD: clamshell_template.scad. The parametric source, for any other size.

What is in it

• One clamshell per 3MF, labelled on the top face with its finished size and the seam allowance included.

• Notches on every curve, each with a tick beside it: at the middle of each lower curve, and at the matching points on the top curve, so you can pin notch to notch.

• The size is the finished width. The template is the cutting line, so it is the finished size plus 1/4" all round: the 4" clamshell measures 4 1/2" across. That is why the label reads INCL 1/4" SA (seam allowance).

How to use it

1. Lay the template on the wrong side of the fabric and draw round it with a fabric marker or chalk.

2. Mark the notches, then cut on the line with scissors. No rotary cutter needed.

3. Lay out the clamshells in rows, each row moved half a shell sideways, so each shell's lower curves sit on the tops of two shells below.

4. Pin notch to notch and sew the curves with a 1/4" seam, easing as you go. The bottom point of each shell lands on the top notch of the shell below.

Clamshells also work for English paper piecing and applique: set the seam allowance to None in the .scad for finished-size templates.

Need another size? Customise in OpenSCAD

Download the .scad file and open it in OpenSCAD (free). Every option below is in its Customizer panel.

• Size: 1 1/2" to 9", or 40 to 230 mm

• Seam allowance: none (finished size), 1/4", 3/8", 7.5 mm or 1 cm

• Notches and label on or off, colours and thickness

Print settings

• Material: PLA

• Layers: 0.2 mm

• Walls: 4, because the edge is the drawing edge

• Infill: 15% gyroid

• Supports: None, flat as supplied

• Elephant foot compensation: 0, so the bottom edge stays true

• Wall order and seam: Outer wall first and a scarf seam. The 3MFs here already have both

Colours

The photos show white with black lettering. The lettering is a single layer on top, so with an AMS that is one filament swap. No AMS? Map both filaments to one spool and run a fine marker over the raised letters.

The design decisions and the testing here are mine, Claude helped with the OpenSCAD.

If it is useful, a like and a make with a photo really help. I read every comment.

Also on MakerWorld: https://makerworld.com/en/models/3562421