Underlay

Underlay is a first layer of light stitching laid down before the top stitches. You don’t usually see it in the finished piece, but it does a lot of work: it stabilises the fabric, stops the top stitches from sinking into it, and gives satin and fills a crisp, supported edge.

Why underlay exists

Fabric moves and compresses as it’s stitched. Without underlay, dense top stitching can pull the fabric in, leaving gaps at the edges of a shape or letting the fabric show through. A layer of underlay tacks the fabric to the stabiliser first and builds a base for the top thread to sit on.

Underlay in Octostitch

Octostitch offers underlay on the stitch types where it matters most, with settings tuned to that stitch:

Fill underlay

Fills can add:

Contour underlay — a run that follows just inside the shape’s outline.
Tatami underlay — a loose fill laid across the top stitching, at its own spacing and angle.

Both use an inset so the underlay sits inside the edge and stays hidden under the top stitches. See Fills.

New fills start with tatami underlay switched on at 1.5 mm spacing and a 1.5 mm inset. It’s the setting a fill wants far more often than not, so it’s the default rather than something to remember; turn it off in the Underlay group when a fill is small enough not to need it.

The angle is relative to the fill

A fill’s underlay angle is stored as an offset from the fill’s own rows, not as an absolute heading. What an underlay is for is holding the cloth in the direction the top stitching can’t, so it has to stay across the fill when the fill is re-angled — which an absolute number doesn’t do. Set it to 90° and it stays square to the rows whatever you do to them.

The pass is staggered by half a stitch from row to row, like the fill itself. Without that, every row would drop its needle in the same place as the row before and the ridge would telegraph through the finished fill.

Satin underlay

Satin columns offer four underlay styles, which you can combine:

Centre-walk — a single run down the middle of the column.
Edge-run — runs down each side, just inside the rails.
Zigzag — one zigzag across the column.
Double zigzag — a zigzag out and a second one back, the return pass shifted half a spacing so its needle holes fall between the outbound pass’s rather than into them.

Zigzag and double zigzag are the same pass sewn once or twice, so picking one clears the other — having both on would just be a denser zigzag arrived at by accident. Double zigzag gives roughly twice the body under a wide column, and because it finishes at the end it started from, it leaves the needle where the next pass wants it.

Both read the same Zigzag spacing: each pass sews at that spacing, and the two interleave.

A narrow inset keeps the underlay tucked under the satin. See Satin column.

How underlay is connected up

Underlay gets covered by the stitching laid over it, which means the needle can walk from one underlay run to the next with real stitches instead of jumping — as long as the walk stays inside the region that later passes will cover.

A straight line does the job on a simple convex shape. For anything with a hole or a concave notch, Octostitch routes around the obstacle rather than falling back to a jump, keeping the travel a little clear of the region’s edges so it stays buried once the fabric shifts under the remaining passes. Where no route is short enough to be worth it — a detour several times longer than the direct distance costs more in thread and time than the trim would — it jumps instead.

The upshot is fewer trims and thread breaks in the underlay pass, with nothing showing on the finished piece. There’s nothing to configure.

When to add underlay

As a general starting point: wider satin columns and larger fills benefit most from underlay, and stretchy or textured fabrics need it more than stable wovens.