A QuiltPlan piecing guide
Square in a Square
A square on point, with every point kept.
One square set on point inside another: a center square with a triangle sewn to each of its four sides. It is in a great many blocks, so it is worth making well. The one thing to protect is the quarter inch beyond each point of the center square. That quarter inch is the seam that joins this unit to the next one, and if it is not there, the points disappear into that seam.
What you cut, for one unit
Shown for a unit that finishes at 4″. Every size is in the chart below.
| Finished unit | Center square, cut 1 | Corner squares, cut 2 | Trim the unit to | Corners cut exact |
|---|---|---|---|---|
| 2″ | 1⅞″ | 2¼″ | 2½″ | 1⅞″ |
| 3″ | 2⅝″ | 2¾″ | 3½″ | 2⅜″ |
| 4″ | 3⅜″ | 3¼″ | 4½″ | 2⅞″ |
| 4½″ | 3⅝″ | 3½″ | 5″ | 3⅛″ |
| 5″ | 4″ | 3¾″ | 5½″ | 3⅜″ |
| 6″ | 4¾″ | 4¼″ | 6½″ | 3⅞″ |
| 7″ | 5½″ | 4¾″ | 7½″ | 4⅜″ |
| 8″ | 6⅛″ | 5¼″ | 8½″ | 4⅞″ |
| 9″ | 6⅞″ | 5¾″ | 9½″ | 5⅜″ |
| 10″ | 7⅝″ | 6¼″ | 10½″ | 5⅞″ |
| 12″ | 9″ | 7¼″ | 12½″ | 6⅞″ |
The corner squares are cut a little big, so the unit can be trimmed square with a quarter inch beyond every point. Short of fabric? The last column is the exact size; it leaves nothing to trim, so sew carefully and only trim the tips. Do not cut the center bigger: trimming would cut its points off. The center sizes are the exact size to the nearest eighth of an inch. At 4″, 7″ and 10″ that eighth is a hair over the exact size, so the points sit about 1/32″ closer to the edge, the width of a thread. At 2″, 4½″, 5″ and 8″ it is a hair under, so the points stop that much short of the seam instead. Either way it is as close as a ruler marked in eighths can get.
Before it is sewn into anything
A finished 4″ unit measures 4½″ before it is sewn into a block. Each point of the center square stops a quarter inch short of the edge, halfway along that side. When this unit is sewn to its neighbor with a quarter inch seam, that seam runs right through the point, and the point just meets it.
Making it
1 · Find the middles
Fold the center square in half and finger-press a crease, then fold it the other way. Each crease marks the middle of two sides. Fold each triangle in half and crease the middle of its long edge. The long edge was cut on the bias and stretches: handle it by its corners and do not iron it.
2 · Sew two opposite triangles
Lay a triangle on one side of the square, right sides together, long edges matched and creases lined up. The tips hang past each end of the side by the same amount, about ⅝″. Sew with a quarter inch seam. Do the same on the opposite side. Press the seams toward the triangles.
3 · Trim the tips
The ends of the two triangles stick out past the square's other two sides. Lay a ruler along each of those sides and trim the tips off level with it, so the next two triangles have a straight edge to sew to.
4 · Sew the last two
Crease, match and sew the last two triangles to the remaining sides the same way, and press toward the triangles. The unit is now a little bigger than it needs to be. That is on purpose.
5 · Trim it to 4½″
Lay a square ruler on the unit so its 2¼″ lines run through the points of the center square, top to bottom and side to side, and its quarter inch lines sit on the two points nearest its edges. Trim those two sides. Turn the unit, line up the trimmed edges and the other two points the same way, and trim the last two sides. For other sizes, trim to the size in the chart, using the lines at half that size.
6 · Check it, then sew it in
It measures 4½″ each way, and every point sits a quarter inch from the edge, halfway along its side. Sewn to the next piece with a quarter inch seam, each point lands right on the seam. If a point is closer to the edge than a quarter inch, it will lose its tip in that seam: sew the next unit with its seams a thread wider.
Good to know
- Pressing. Toward the triangles keeps the bulk out of the center. If the center is much darker than the corners and shows through them, press these seams open instead.
- Why two corner squares, not one? A square cut once on the diagonal puts straight grain on the triangle's two short sides, which become the outside edges of the unit, so the unit keeps its shape. Cutting one square twice would put stretchy bias on the outside.
- Where the numbers come from. The center square finishes at the finished size divided by 1.414 (that puts its points exactly on the unit's edges), plus half an inch for its seams. The corner triangles' short sides finish at half the unit; a quarter inch all round adds just under ⅞″ to them (0.854″), and these are cut ⅜″ bigger again for trimming.
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