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Two per cent of slippage is two per cent of fabric weight, banded at one machine revolution.
Feeder Slippage
—%
Delivery shortfall against the wheel circumference
Loop Length, Weight Error & Banding
Fabric Weight Error
—%
Loop Length Delivered
—mm
Loop Length Error
—mm
Fabric Weight Delivered
—g/m2
Banding Repeat Spacing
—cm
Weight Spread from Feeder Variation
—g/m2
Loop Length Spread
—mm
Theoretical Delivery
—mm/rev
Delivery Shortfall
—mm/rev
The model assumes the feeder wheel is the delivery reference and that loop length scales directly with delivered yarn, which holds for a positive feeder controlling supply but not for a tension-controlled or negative feed, where loop length is set by yarn tension against the cam and this calculation does not apply. Measured delivery must be taken over many revolutions; a single revolution cannot be measured to the precision the arithmetic implies. Slippage is not a fixed property of a feeder - it rises with downstream tension, so a reading taken at one machine speed or fabric take-down setting does not transfer to another. The feeder-to-feeder spread is entered as a range rather than derived, and it needs measurement across a representative sample of feeders rather than the two that were easiest to reach. Fabric weight here is the greige figure at the stated stitch density and will move substantially through relaxation and finishing.
Using this calculator
About the Positive Feeder Slippage, Loop Length Error & Barre Spacing
The formula
This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.
What one wrap of the wheel should delivertheoretical = pi x wheelDiameter slippage = ( theoretical - measured ) / theoretical x 100
The yarn wraps the wheel, so one revolution should pay out one circumference. It never quite does: the yarn creeps against the wheel surface under tension, and the deficit is the slippage.
Slippage lands directly on loop lengthactualLoop = targetLoop x ( 1 - slippage / 100 )
A positive feeder exists to fix loop length by controlling yarn supply rather than yarn tension. When it under-delivers, the needles take a shorter loop, and the fabric gets lighter in exact proportion.
Loop length to fabric weightgsm = coursesPerCm x walesPerCm x loopLength x tex / 100
Weight is linear in loop length, which is why a two per cent delivery error is a two per cent weight error - and why fabric weight is the most sensitive routine check on feeder condition.
Where the stripes appearbandPeriod = feeders / coursesPerCm
Every feeder knits one course per machine revolution, so the feeder sequence repeats every 96 courses. At 17 courses per centimetre that is a 5.65 cm repeat, and any feeder that differs from its neighbours prints a stripe at exactly that spacing.
Symbols used above
Symbol
Stands for
Unit
positive feeder
Storage feeder delivering a fixed yarn length per revolution
—
slippage
Shortfall of delivered yarn against wheel circumference
%
barre
Horizontal banding across the fabric from course-to-course variation
—
band period
Vertical distance between repeats of the feeder sequence
cm
How the result is derived
Step by step, from the values you type to the figure on screen.
The 9 inputs are read from the form on every keystroke: Feeder Wheel Diameter, Measured Delivery per Revolution, Target Loop Length, Feeder-to-Feeder Spread, Courses, Wales, Yarn Count, Target Fabric Weight and Feeders.
Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
The validated values are substituted into the expression above, which resolves Feeder Slippage together with every supporting figure in one pass — no value is carried over from a previous entry.
The supporting outputs — Fabric Weight Error, Loop Length Delivered, Loop Length Error, Fabric Weight Delivered, Banding Repeat Spacing, Weight Spread from Feeder Variation, Loop Length Spread, Theoretical Delivery and Delivery Shortfall — come from the same pass, so they always describe the same case as the headline figure.
Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.
What each input means
Where to read each value on the floor, the unit it must be in, and the range the tool accepts.
Input
Unit
Accepted range
Default
What it means
Feeder Wheel Diameter
mm
10 to 200 mm
52
Measured Delivery per Revolution
mm
5 to 700 mm
159.8
Target Loop Length
mm
0.5 to 20 mm
2.9
Feeder-to-Feeder Spread
%
0 to 10 %
0.8
Range of slippage across the feeders
Courses
/cm
2 to 80 /cm
17
Wales
/cm
2 to 80 /cm
13
Yarn Count
tex
2 to 200 tex
20
Target Fabric Weight
g/m2
20 to 900 g/m2
128
Feeders
—
1 to 250
96
What the tool returns
The headline figure and every supporting value it is built from.
Output
Unit
What it tells you
Feeder Slippage (headline result)
%
Delivery shortfall against the wheel circumference
Fabric Weight Error
%
Loop Length Delivered
mm
Loop Length Error
mm
Fabric Weight Delivered
g/m2
Banding Repeat Spacing
cm
Weight Spread from Feeder Variation
g/m2
Loop Length Spread
mm
Theoretical Delivery
mm/rev
Delivery Shortfall
mm/rev
Worked example
Given
0
52 mm feeder wheel measuring 159.8 mm delivered per revolution
1
Target loop length 2.9 mm, 0.8% spread across feeders
2
17 courses and 13 wales per cm, 20 tex yarn
3
Target weight 128 g/m2, 96 feeders
Substituting
theoretical = pi x 52 = 163.3628 mmslippage = ( 163.3628 - 159.8 ) / 163.3628 = 2.1809%loop = 2.9 x ( 1 - 0.021809 ) = 2.8368 mmgsm = 17 x 13 x 2.8368 x 20 / 100 = 125.3845band = 96 / 17 = 5.6471 cm
Answer
0
Theoretical delivery 163.3628 mm, so 2.1809% slippage
1
Loop length 2.8368 mm, 0.0632 mm short of target
2
Fabric at 125.3845 g/m2, 2.0434% under target
3
Banding repeats every 5.6471 cm
4
Feeder spread of 0.0232 mm gives 1.0254 g/m2 of weight variation
The band spacing is the diagnostic worth keeping. If a knitter reports faint horizontal stripes and a ruler puts them 5.6 cm apart on this machine, the cause is in the feeder set and not in the yarn - because that spacing is a property of feeder count and course density and nothing else. Stripes at a different spacing point somewhere else entirely, most often at a package or a creel.
How to use it
Work through the input groups in order — Feeder Delivery and Fabric. The defaults are a realistic case, so you can change one value at a time and watch what moves.
There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
Read Feeder Slippage in the dark results panel — that is the headline figure, expressed in %.
Check the supporting rows underneath (Fabric Weight Error, Loop Length Delivered, Loop Length Error, Fabric Weight Delivered, Banding Repeat Spacing, Weight Spread from Feeder Variation, Loop Length Spread, Theoretical Delivery and Delivery Shortfall) before acting on the headline — they are where an implausible input usually shows itself first.
Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.
Where this is used
Process planning — establishing Feeder Slippage before a trial is booked, so machine time and material in Knitting, Hosiery & Stretch-Fabric Control are committed against a calculated figure rather than an estimate.
Costing and quotation — Feeder Slippage is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Feeder Wheel Diameter) shows how much of the gap in Feeder Slippage each variable explains.
Teaching and study — the accepted ranges bracket normal Knitting, Hosiery & Stretch-Fabric Control practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.
Reading the result
Typical bands and what each one is telling you.
Value
What it indicates
Slippage under 1%
A clean, correctly tensioned feeder with a good wheel surface.
1 - 3%
Normal running. Consistent across feeders it is a calibration offset, not a fault.
Above 4%
Worn or contaminated wheel, wrong wrap count, or excessive downstream tension.
Spread above 1%
Feeder-to-feeder variation large enough to band the fabric visibly.
Assumptions and limits
The model assumes the feeder wheel is the delivery reference and that loop length scales directly with delivered yarn, which holds for a positive feeder controlling supply but not for a tension-controlled or negative feed, where loop length is set by yarn tension against the cam and this calculation does not apply. Measured delivery must be taken over many revolutions; a single revolution cannot be measured to the precision the arithmetic implies. Slippage is not a fixed property of a feeder - it rises with downstream tension, so a reading taken at one machine speed or fabric take-down setting does not transfer to another. The feeder-to-feeder spread is entered as a range rather than derived, and it needs measurement across a representative sample of feeders rather than the two that were easiest to reach. Fabric weight here is the greige figure at the stated stitch density and will move substantially through relaxation and finishing.
Every input is bounded to the range normal practice occupies (Feeder Wheel Diameter 10 to 200 mm, Measured Delivery per Revolution 5 to 700 mm and Target Loop Length 0.5 to 20 mm, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.
Standards and further reading
ISO 4921 - knitting, basic concepts, vocabulary.
ISO 3801 - determination of mass per unit length and mass per unit area.
ASTM D3887 - tolerances for knitted fabrics.
ISO 16549 - textiles, unevenness of textile strands, capacitance method.
Questions people ask
Is uniform slippage across all feeders actually a problem?
Not for appearance, only for weight. If every feeder slips by the same 2.18%, every course is identically short and the fabric is perfectly uniform - just 2% lighter than intended, which is caught at the weighing scale and corrected by adjusting the target delivery. That correction is entirely legitimate and is what the machine setter does routinely. The problem is the spread, not the mean: feeders that slip differently produce courses of different loop length in a fixed repeating sequence, and that is a defect no scale detects and no adjustment corrects. This is why the two figures are reported separately, and why the spread deserves the closer attention of the two.
Why does slippage happen at all if the yarn is wrapped round the wheel?
Because the grip is frictional and the yarn is elastic. The wraps hold the yarn by capstan friction, which depends on the wrap angle, the surface condition of the wheel and the tension difference across it - and under the downstream tension the knitting zone applies, the yarn creeps backwards slightly against the wheel rather than moving with it perfectly. Anything that lowers friction raises slippage: a polished or wax-contaminated wheel, too few wraps, lubricated or filament yarn. Anything that raises downstream tension does the same, so a tight setting, a heavy fabric take-down or a needle problem all show up as increased slippage. That last route is worth remembering, because it means a slippage change can be a symptom of a fault somewhere else entirely.
How is the delivered length measured in practice?
By marking the yarn upstream of the feeder and counting wheel revolutions, or on modern machines by reading the delivery counter the feeder itself reports and checking it against a physical measurement. The physical check matters because the counter reports wheel revolutions converted by an assumed circumference, which is exactly the quantity in question - a worn wheel reads correct and delivers short. Ten or twenty revolutions should be measured rather than one, since a single revolution of 163 mm cannot be measured to the tenth of a millimetre this calculation implies. Where a machine has a fabric-length or yarn-length counter, comparing its total against the sum of the feeders is a useful cross-check.
Does the banding always appear at the calculated spacing?
It appears there when the cause is feeder-related, which is what makes the spacing diagnostic. The calculated period is set only by feeder count and course density, so on this machine it is 5.65 cm regardless of what the feeders are doing wrong. Stripes at other spacings have other causes: package-related variation appears at intervals set by how much yarn a package holds, which is metres rather than centimetres; a single faulty feeder produces one line per repeat rather than a gradient; and dyeing or yarn-lot barre has no fixed geometric period at all. Measuring the spacing before opening the machine is therefore the cheapest diagnostic step available, and it is routinely skipped.
