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Zigzag Stitch Mechanism
The lock-stitch machine already published sews a straight line, and a straight line of thread cannot stretch - which is why early machines could not sew knitted cloth, finish a raw edge, or work a buttonhole. The next rung is a mechanism that swings the needle bar sideways between stitches, driven by a cam turning with the main shaft.
**US 1,466,150**, "Zigzag mechanism for sewing machines", Ralph M. Sharaf, filed 2. April 1917, granted 28. August 1923: a cam-driven vibration of the needle bar while the machine stitches, with the throw adjustable. Domestic zigzag machines followed in the 1950s.
**You build the motion in wood** - a cam, a follower and a pen drawing the needle's path - then sew both stitches on jersey and pull them until something gives.
Intermediate
3 hours
Instructions
1
1
Cut a cam
Cut a cam
From 18 mm plywood cut a 60 mm disc and drill its pivot hole 5 mm off centre: that offset is half the zigzag width. Cut a second disc with a 10 mm offset for a wider stitch.
Materials for this step:
Plywood Sheet1 pieceTools needed:
Hand Saw
Cordless Drill
Steel Ruler2
2
Follower and needle bar
Follower and needle bar
Screw a pivoted arm to the board so one end rides on the cam's edge and the other carries a dowel - the needle bar. A spring keeps the follower against the cam. Tape a marker to the dowel.
Materials for this step:
Machine Screws4 pieces
Compression Spring Assortment1 set
Dowel Rod1 piece
Permanent Marker1 pieceTools needed:
Hot Glue Gun
Bench Vise3
3
Draw the stitch
Draw the stitch
Pull a strip of graph paper steadily under the pen while turning the cam by hand, one turn per stitch. Measure the width of the trace; swap cams and repeat. Lock the follower to draw a straight line for comparison.
Materials for this step:
Graph Paper1 sheet
Masking Tape1 rollTools needed:
Steel Ruler4
4
Sew the real thing
Sew the real thing
Cut six 200 x 50 mm jersey strips. Join them in pairs with a 100 mm seam: straight stitch, zigzag 3 mm, zigzag 5 mm, all at 2.5 mm stitch length.
Materials for this step:
T-Shirt Jersey Fabric Bundle1 piece
Polyester Thread10 metersTools needed:
Sewing Machine
Fabric Scissors5
5
Pull until it gives
Pull until it gives
Mark 100 mm across each seam. Pull each pair apart steadily by hand and note the marked length when the thread snaps - or when it does not, and the cloth simply stretches.
Tools needed:
Steel Ruler
Tape Measure6
6
Thread geometry and your results
Thread geometry and your results
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7
History & Context
History & Context
**What the patent specifies:** a cam-driven mechanism that vibrates the needle bar laterally during stitching, with adjustable throw. **Modern build (derived):** a plywood cam and follower drawing the path, plus real seams for the test.
The same sideways swing gave overcast edges, buttonholes and decorative stitches, and cam stacks later let a machine select a pattern. Its limits: a zigzag uses more thread, can tunnel thin cloth if the tension is wrong, and the needle bar's sideways travel puts a limit on machine speed.
Materials
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Tools Required
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