Pattern Area measurement: Manual method – Part 6
…Continued from Part-5
9. RSM: The first scientific method to estimate leather consumption was published in 1922 by W.W. Russ and F.L.Small in Boston, USA. Assume this is further extension of SLM. Their method consists of interlocking a Pattern until four patterns are facing the same direction. Then similar points on these patterns are joined to form a parallelogram. This is the area which covers one complete pair of patterns plus ‘first waste’ i.e interlocking wastage. This is the smallest possible area in which one pair of patterns could be cut. Additional allowances are added to this from the standard tables.
Note: A detailed method of laying and finding the parallelogram is explained in Pattern Area measurement -Synthetic chapter.
The factors which effect the cutting results are given below.
- Scale pattern area by parallelogram method.
- Adjusting for second waste which depends on average scale pattern area & area of skin.
- Adjusting for the type of skin by using “ leather type coefficients”
- Adjustments for shoe size and fitting.
- Adjusting for the area discrepancy and cuttability of leather by adjusting net coefficient.
- Pattern area: This is the actual net area of the individual pattern item and the first wastage/ interlocking waste. The first waste is the area between the two patterns, when interlocked due to irregular in shape. This Pattern area is also called as “scale area” and used as the basis for further phases in the system.
- Second waste: When cutting uppers, the clicker not only gets waste between patterns, but also gets extra waste when goes closer towards the edge of the skin. The second waste depends on the area of the skin and pattern (Larger the area the smaller the waste and the smaller the area the larger the waste).
Pattern scale area when added with the second waste allowances is called GROSS AREA (G). This depends on different kind of leather also. For calculating G we use certain empirical formulas as
For Full grain side G= S (1.205+S/A)
S= Average scale pattern area,
A= Average area of the skin
1.205 = this is an area addition that forms part of the mathematical equation. This is a constant factor for a particular kind of skin.
If S/A > 0.185 i.e. if the pattern item size is bigger than the skin size then
G=S (1.02+2 S/A)
In case of suede G = S (1.098+S/A)
Find the Second wastage from Table 1.
Note: if you are working for full pair take the average pattern area and find out the suitable second wastage.
1. Adjusting for the type of skin: If we are using different type of leathers then add some allowance towards this. Use table 2.
2. Adjustment for size and fittings: Different shoe sizes and fittings will require different cutting areas. The difference in cutting area between sizes and between one fitting is same.
For example in English size system ±5% material allowances to be added higher/lower size, while in French system ±3.5 % material allowances is given for each size.
- Adjusting for area discrepancy and Cuttability of leather (Third wastage): Cuttability relates to the grades of leather. On first grade leather normally an allowances of 3% is given , while consecutive grades have 5%.
There will be a difference between actual and tanners quoted are called area discrepancy. So we have to adjust for the are discrepancy and cuttability of the leather.
Then find out the standard coefficient.
Standard Coefficient = discrepancy coefficient *cuttability coefficient
(Assume tanner quoted that leather is 10 sq.ft . But it is actually 9.8 sq.ft, then the
discrepancy coefficient= actual area/ quoated area. i.e 9.8/10= 0.98
Ex: Standard Coefficient = discrepancy coefficient *cuttability coefficient (Assume leather is B grade) = 0.98 X 0.92= 0.9016
a) If corrected grain take 5% less from the total norm
b) If lining material used for heel grip take 8% less from the total norm.
c) No third wastage for synthetics.
General points while calculating Allowance
a) Whatever method of costing is used, try more than one method of arranging component shapes, so that the most economical arrangement is found.
b) Multilayer cutting is less economical and you need to allow extra amounts of material.
c) It is desirable that clickers should beat the costing, whenever possible and they should be encouraged to do so. Some clickers find it easier to cut in a more economical way than others.
An example how the norms calculated using this method along with tables showed in next chapter. i.e Pattern Area measurement Manual methods -Part 7)