How Many Warp Specifications a Weaving Shed Can Afford

How to read this sheet

The test this sheet returns is worth more than the answer, because it can be applied to the next specification before it exists. Divide what a drawing-in costs over a tie-in by what it would cost per metre to run the fabric on the nearest specification you already carry, and that is the metreage the warp has to deliver every time it is gaited. Anything short of it is cheaper woven on somebody else's sett. Ask the question when the fabric is being developed rather than three years later when it has a history. The cost of merging is the input everything turns on and it is the one people will not write down. A fabric moved onto a neighbouring sett takes more yarn if the sett is heavier, loses a little of its hand if it is not, and may need a price concession or carry more seconds - all of which are real and none of which appear in any system. Estimate it honestly and expect the long tail of the range to fail the test anyway; estimate it generously and the sheet will simply agree with whatever is already being done. Read the two share columns together. The pattern is always the same: a handful of specifications carry a very small share of the metres and cause a very large share of the changeovers, and they are not bad fabrics - they are short runs on their own warp, which is a different failing and one nobody is blamed for. What is not modelled. Sequencing is outside this sheet: grouping similar warps so that more changeovers become tie-ins is worth money on the range as it stands, and the free changeover sequencing calculator on this site prices it - do that first, because it may save enough to keep a specification that would otherwise fail here. Colour is treated as part of the specification, which is right for a dyed warp and unnecessarily strict for a greige one that is piece-dyed later. Nothing is said about the customer who will not accept the neighbouring sett, which is the commonest reason a specification survives a review it should not have. And a specification kept for a strategic account is a decision rather than an error; the sheet prices it so the decision is taken knowingly.