Winding on must take up yarn at exactly the speed the front rollers deliver it, with a light, steady tension. If the bobbin winds faster than delivery the yarn is stretched and breaks at its thin places, and if it winds slower the yarn slackens, loops and kinks. Because the bobbin grows thicker as it fills, a fixed drive cannot hold this balance and the drive must be self-adjusting or progressively changed.
Part of Spinning Frame
Collecting finished yarn onto a bobbin at the delivery rate, with even tension and even layers.
The Bobbin Grows, So The Winding Speed Cannot Stay Fixed
Yarn arrives at a fixed length per minute set by the front rollers. The bobbin takes up one circumference of yarn per turn it makes relative to the flyer, and that circumference rises as layers build up. On a bobbin of 25 mm barrel diameter one turn takes up π × 25 = 79 mm. When the bobbin has filled to 45 mm one turn takes up π × 45 = 141 mm. To take up the same length each minute the bobbin must turn fewer times relative to the flyer as it fills: Bobbin and Whorl works the speeds out.
The overview states the working rule: the flyer runs slightly faster than the bobbin, and the speed difference controls the winding rate. Equal speeds add twist and wind nothing on.
Three Things Go Wrong If The Balance Is Off
- Winding too fast. Tension climbs; the yarn is stretched and parts at its thinnest places, usually at the flyer eye. The weaker the yarn, the sooner.
- Winding too slowly. Yarn builds up slack between the rollers and the flyer, forms loops and snarls, and sometimes wraps the spindle.
- Uneven traverse. If the yarn is laid in one place, the bobbin builds up a hill that sheds yarn in lumps when it is unwound on the loom or warping frame.
What You Need
- A bobbin that fits the spindle with a smooth barrel and flanges (Bobbin and Whorl).
- A tension device: a friction brake on the bobbin whorl (the Scotch-tension arrangement of the hand wheel in Spinning Wheel) or a pair of whorl sizes.
- A way to lay yarn along the bobbin: the flyer eye or the bobbin must traverse.
Method: Setting The Winding
Step 1: Start with the brake light. On a frame with a bobbin brake begin with a low brake load. The yarn should wind on with no slack between flyer and rollers and no visible stretch.
Step 2: Watch the yarn between the flyer eye and the front rollers. It should hang in a smooth, slightly curved path. A straight, humming line is too tight; loops are too slack.
Step 3: Check at the start and at the end. Tension at an empty bobbin differs from tension at a nearly full one; adjust the brake to suit the half-full state, then watch both ends.
Step 4: Inspect the layers. Even, parallel layers lying neatly from flange to flange mean the traverse is right.
Worked Example
A bobbin of barrel 25 mm, full diameter 45 mm and length 100 mm (assumed dimensions for illustration) holds the annulus π/4 × (45² − 25²) = 1,100 mm² over 100 mm, which is 110,000 mm³. Yarn packed at 60% (an assumed fraction) and 0.2 mm thick (an assumed diameter for Ne 20) occupies 110,000 × 0.6 ÷ (π/4 × 0.2²) = 2.1 million mm, 2.1 km. At 29.5 g per km that is about 62 g. At 152.4 m per hour (twisting at 20 per inch, 2,000 rpm) the bobbin fills in 2,100 ÷ 152.4 = 13.8 hours.
Common Mistakes
- Fixing a snarl by tightening the brake until the yarn then breaks. Check the delivery first.
- Different brake loads on neighbouring spindles, giving bobbins of different density and weight.
- Unrounded bobbin flanges that scrape the yarn.
Safety
Wound-up yarn and moving flyers
Never reach to straighten a loop or free a snarl while the flyer is turning; a hand held near a moving flyer arm is struck, and yarn wound round a finger tightens at once. Stop the frame, wait for it to halt, then clear it. The warning in Doffing applies in full.
What’s Next
- Learn next: Bobbin and Whorl — the speed difference worked out in numbers
- Combine with: Flyer Mechanism — the part that turns the yarn and guides it onto the bobbin