A cop winder is a textile mill machine that winds yarn from a supply package onto a tapered, self-supporting cylindrical mass called a cop, used as weft in shuttle looms. It solves the problem of feeding loom shuttles with a compact, spindleless yarn package that unwinds cleanly from the inside out at high speed. A traverse mechanism shifts the yarn guide along a short stroke while the spindle rotates, building the cop in conical layers. A typical cop winder produces a 150–250 g package at 600–1200 m/min winding speed for cotton weft on Lancashire and Northrop-style shuttle looms.
Cop Winder Interactive Calculator
Vary cop diameter and spindle speed to see yarn winding speed and a live animated cop-winder traverse diagram.
Equation Used
The calculator uses the cop surface-speed equation. Convert the effective cop diameter to metres, multiply by pi and spindle RPM, and the result is the yarn winding speed in metres per minute.
- Effective cop diameter is the active winding layer diameter.
- Spindle RPM is steady with negligible belt slip.
- Yarn speed equals cop surface speed at the winding point.
- Diameter is converted from mm to m before calculation.
Operating Principle of the Cop Winder
A cop winder takes yarn off a ring-spun bobbin or larger feed package and lays it onto a rotating spindle in a precise conical traverse, building a self-supporting yarn body with no permanent core. The shape matters because the cop has to slide into a shuttle, sit there for the life of the pick, and then unwind from the nose end without collapsing — that geometry is what lets a Lancashire loom fire weft across a 60-inch shed in under a second without snags.
The mechanics are simple but tightly toleranced. A driven spindle rotates at 3000–6000 RPM. A yarn guide rides on a traverse bar driven by a heart-shaped cam that pulls the guide up the spindle slowly and drops it back fast — the classic chase build that makes each layer cross the previous one at a small build angle, usually 15–22°. The yarn passes through a tensioner (typical setting 8–15 cN for 30s cotton) before reaching the guide. If the build angle is too shallow, layers slough off when the cop gets handled. Too steep, and the unwinding balloon catches the nose and snaps the yarn at the loom — what mill mechanics call "sloughing off" or "stitching."
Common failure modes are predictable. A worn traverse cam gives uneven layer spacing and a soft cop that crushes in the shuttle. A glazed yarn tensioner pad lets tension drift, producing a soft package density below 0.45 g/cm³ that runs out of yarn early. A bent spindle wobbles the package, and you'll see oscillating tension marks and bulging at the cop nose within the first 50 g of build.
Key Components
- Spindle: Rotating shaft, typically 8–12 mm diameter and 180–250 mm long, that carries the cop. Runs at 3000–6000 RPM with a runout tolerance of 0.05 mm or better — anything looser produces visible package wobble and uneven density.
- Traverse cam: Heart-shaped or grooved cam that drives the yarn guide along a short axial stroke, usually 50–80 mm. The slow-rise fast-return profile produces the conical chase that gives the cop its self-supporting nose and lets it unwind without collapsing.
- Yarn guide (traveller eye): Polished ceramic or chromed steel eye that the yarn passes through onto the spindle. Surface finish must be Ra ≤ 0.2 µm — any rougher and the yarn frays, raising hairiness and breaking at the loom shed.
- Tensioner: Disc or post-type tensioner that holds yarn tension in the 8–15 cN range for medium cotton counts. Drift outside this band changes package density directly: low tension gives a soft cop, high tension gives a hard cop that won't unwind freely.
- Drive belt and headstock: Connects the line shaft or individual motor to the spindle. Slip above 2% causes RPM drop under heavy yarn pull, varying the build angle layer-to-layer and giving the cop a barrel shape instead of a clean cone.
- Stop motion: Mechanical or electrical sensor that drops the spindle drive when the yarn breaks. Response time under 200 ms — slower than that and you wind several metres of slack onto the cop, which jams in the shuttle.
Real-World Applications of the Cop Winder
Cop winders sat at the heart of every shuttle-weaving mill from the late 19th century through the mid-20th, and they still run in heritage operations and certain narrow-fabric mills today. The reason is the package geometry — a cop unwinds inside-out from the shuttle, which means no spindle, no flange, and no bobbin to eject after each pick. That makes it the lightest possible weft package, and on a high-speed shuttle loom every gram of moving mass costs energy and shortens shuttle life. Modern projectile and rapier looms use different feed packages, but anywhere a Northrop, Lancashire, or Crompton shuttle loom is still running production, a cop winder is somewhere upstream feeding it.
- Heritage cotton weaving: Queen Street Mill in Burnley, Lancashire — the last steam-powered weaving shed in the world — runs cop winders to feed its 308 Lancashire looms producing heavy cotton cloth.
- Narrow fabrics: E. Oppermann GmbH in Germany winds cotton and viscose cops for shuttle-loom production of jacquard ribbons and labels.
- Industrial textiles: Filter cloth weavers using older Saurer 100W shuttle looms still rely on cop winders for heavy spun-polyester weft packages.
- Carpet and rug weaving: Wilton and Axminster carpet mills, including some Brintons heritage lines, use cop winders for woollen weft on shuttle-driven gripper Axminster machines.
- Living-history museums: Lowell National Historical Park in Massachusetts operates restored cop winders alongside its Draper Northrop looms as part of the working-mill demonstration.
- Specialty handloom supply: Indian khadi and handloom cooperatives wind cotton cops on small bench-top cop winders for traditional pit-loom and frame-loom weavers.
The Formula Behind the Cop Winder
The single number a cop winder operator cares about is winding speed — the linear metres of yarn laid onto the package per minute. That figure controls how long it takes to fill a cop, how much tension the yarn sees, and whether the build geometry stays stable. At the low end of the typical range (around 400 m/min) the package builds slow and tight, ideal for fine combed cotton but uneconomic for production. Around 800 m/min is the sweet spot for medium counts on a heritage Lancashire-style line — fast enough to fill a 200 g cop in under 2 minutes, slow enough that yarn tension stays in the 10–12 cN band. Push above 1500 m/min and you start fighting balloon tension at the unwinding feed package, and breakage rates climb sharply.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| vw | Yarn winding speed at the cop surface | m/min | ft/min |
| Dcop | Effective cop diameter at the layer being wound | m | in |
| Nspindle | Spindle rotational speed | RPM | RPM |
Worked Example: Cop Winder in a heritage shuttle-weaving mill in Lancashire
A working-museum weaving shed in Burnley is setting up a restored Universal Winding cop winder to feed its 1920s Lancashire looms. They want 200 g cotton weft cops at 36 mm finished diameter, wound from 30s combed cotton at a target winding speed that keeps tension at 11 cN and finishes a cop in under 2 minutes. The spindle is rated to 5000 RPM but the headstock pulleys give 4000 RPM as the standard setting.
Given
- Dcop = 0.036 m
- Nspindle (nominal) = 4000 RPM
- Cop mass target = 200 g
- Yarn linear density (30s cotton) = 19.7 tex
Solution
Step 1 — at the nominal 4000 RPM spindle speed, calculate the surface winding speed at the finished cop diameter:
Step 2 — convert to a yarn mass throughput using the 30s cotton tex value (19.7 g per 1000 m):
Step 3 — divide cop mass by throughput to get build time at nominal:
That is far too long — the operator needs the cop in under 2 minutes. The issue is that early in the build the cop diameter is much smaller than 36 mm, so the early surface speed is far below 452 m/min. At the low end of the build (say D = 10 mm bare spindle):
That feels almost stationary — yarn dribbles onto the spindle at barely 2.5 g/min. To pull the average build time down, the operator runs the spindle at the high end of its rating, 5000 RPM, until the cop builds out:
At 565 m/min surface speed the throughput climbs to 11.1 g/min at full diameter, and averaged across the build (small to large) a real 200 g cop fills in roughly 6–8 minutes — still slower than a modern winder, but matched to the loom's own pick rate.
Result
Nominal full-diameter winding speed lands at 452 m/min with a yarn throughput of 8. 9 g/min at full cop diameter. In practice that feels like a steady, quiet wind — the package grows visibly but slowly, and an operator can watch tension drift on the disc tensioner and intervene before a soft layer forms. The build sweeps from 126 m/min when the spindle is bare up to 565 m/min at 5000 RPM full diameter, and the sweet spot for a clean conical chase sits in the 400–500 m/min band. If your measured build time runs 30% long compared to this calculation, the most common causes are: (1) drive belt slip above 2% that pulls actual spindle RPM well below the dial reading — verify with a hand tachometer on the spindle nose; (2) a glazed tensioner pad letting yarn tension drop below 8 cN, which gives a soft low-density cop that mass-checks light; or (3) a worn traverse cam that produces uneven layer chase and visible barrelling at the cop waist instead of a clean cone.
Cop Winder vs Alternatives
Cop winders compete with two later package formats — pirn winders, which build onto a wooden or plastic pirn for automatic shuttle-changing looms, and cone winders, which feed modern shuttleless looms. The choice depends entirely on what loom the weft is going into.
| Property | Cop winder | Pirn winder | Cone winder |
|---|---|---|---|
| Winding speed | 400–1200 m/min | 600–1500 m/min | 1200–2200 m/min |
| Package mass | 150–250 g | 60–120 g | 1.5–2.5 kg |
| Target loom type | Manual-loaded shuttle looms (Lancashire, narrow fabric) | Automatic shuttle-change looms (Northrop, Draper) | Rapier, projectile, air-jet, water-jet |
| Package core required | None — self-supporting | Wooden or plastic pirn | Cardboard or plastic cone |
| Capital cost per spindle | Low — simple cam-driven traverse | Moderate — pirn handling adds complexity | High — electronic yarn clearing standard |
| Maintenance interval | Cam and tensioner check every 500 hr | Pirn-feed mechanism check every 250 hr | Splicer service every 2000 hr |
| Typical mill era | 1880s–1950s, heritage today | 1900s–1970s | 1960s–present |
| Yarn break recovery | Manual piecing | Manual piecing | Automatic splicer |
Frequently Asked Questions About Cop Winder
That's almost always a build-angle problem at the cop nose. If the chase angle is steeper than about 22°, the inner layers form too sharp a cone and the unwinding balloon catches the nose lip as the package empties — you'll see it fail right when the diameter drops back to the spindle line. Pull the traverse cam and check the rise-to-return ratio. A standard heart cam wears at the fast-return flank first, which steepens the effective angle as the cam ages.
Quick check: measure the unwound cop after a controlled test pick. The nose should taper smoothly from full diameter to bare in roughly 15–18 layer crossings. Fewer than that and the cam needs replacing.
Mechanically yes, but the tension setting and traverse stroke change. Finer counts (60s and above) need lower tensioner settings — drop from the standard 11 cN down to 6–8 cN, otherwise the higher specific surface area of finer yarn gives proportionally higher friction at the guide eye and yarn breaks climb. The traverse stroke also wants to be 10–15% shorter for fine counts to keep the cop nose stable, because finer yarn has less mechanical lock between layers.
For coarse weft (10s–20s) the same machine runs at full stroke and tension. The spindle RPM stays the same — what changes is the yarn package management.
Pirn winder, without question. The Northrop loom's defining feature is its automatic pirn-change battery — the loom ejects spent pirns and inserts fresh ones without stopping. A cop has no core to grip in the changer fingers, so cops physically cannot run in a Northrop. Cop winders feed manually-loaded shuttle looms like the Lancashire or older Crompton & Knowles plain looms.
If you're restoring a mixed shed with both loom types, you need both winders — they are not interchangeable.
Low package density at correct diameter means the layers are loose. The dominant cause is yarn tension drift below the 8 cN floor — check the tensioner discs for glazing or fibre buildup between the plates, which de-couples the spring force from the actual yarn pull. A cleaning with isopropanol and a felt-pad replacement usually restores density to spec.
Second likely cause: spindle RPM measured below dial setting due to drive belt slip. A soft package built at 3500 RPM instead of 4000 RPM will mass-check 12–15% light at correct diameter because each layer crosses fewer times per unit length.
That is traverse reversal dwell — the cam is pausing too long at top and bottom of stroke, dumping extra yarn at the cop ends. On a worn cam, the dwell at end-of-stroke grows as the follower wears into the cam profile. You can confirm by marking the yarn guide position and timing the dwell with a stopwatch against spindle revs — anything more than 3–5 spindle revolutions of dwell at each end will produce visible barrelling.
Fix is cam replacement or, on adjustable-stroke machines, shortening the traverse by 2–3 mm to move the wear point.
Yes, and many heritage restorations do this — but the spindle bearings and balance limit you, not the motor. Original line-shaft cop winder spindles are typically rated to 5000–6000 RPM with plain bronze bushings. Push past that with a high-resolution servo and you'll see bearing-temperature rise and visible package wobble within minutes. Stay inside the original RPM rating and use the VFD purely for soft-start and consistent speed regulation, which actually improves package density consistency by eliminating belt-slip variation.
One catch: the traverse cam is mechanically coupled to spindle rotation in most original designs, so changing spindle RPM changes traverse rate proportionally. The chase angle is preserved, which is what you want.
References & Further Reading
- Wikipedia contributors. Bobbin. Wikipedia
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