HQ Sixteen: Custom Small-arc Quilting Ruler

For reasons not relevant here, Mary is completing a friend’s quilt for the family. Part of the existing design involves stitching arcs around each side of a myriad small blocks across the quilt:

After free-motion quilting a few blocks, Mary decided the peak of the curve looked good at ⅜ inch from the block edge. This sort of thing is generally done by “ruler quilting” with the machine’s foot guided by a ruler, but none of her considerable assortment of quilting rulers had exactly the arc required for that curve.

The stitch path will be ¼ inch away from the edge of the ruler, as set by the ½ inch OD Handi-Feet Sure Foot centered on the needle:

Knowing the blocks are 2-¼ inch on a side and the arc is ⅜ inch tall, the Chord Equation gives the 1-⅞ inch radius of the circle matching the arc. Using proper terminology:

• Block side = chord
• Arc height = sagitta

With those numbers in hand, producing a suitable quilting ruler is straightforward:

The legends are backwards, because the lines must be engraved on the bottom of the ruler to eliminate parallax through the ¼ inch acrylic sheet:

She can now eyeballometrically align the engraved square with the edges of the block to put the curved edge at the right place to guide the foot:

After half a dozen blocks, she reports the ruler works as intended and the duplicated Start / Stop buttons on the improved hand grips let her control the machine with either thumb. She uses Stitch Regulator mode to produce a uniform line of stitches regardless of speed variations around the arc.

Now she can finish the quilt and have all those curves look the way she wants.

I knew that laser cutter would come in handy …