How offcut allowances are used
There are two offcut allowances to set for system parameters.
- Offcut allowance for restocking
- Offcut allowance for cost reduction
Typically, offcuts are off less value than a full sheet. When offcuts are added back to the board library (restocking) they are added at a lower cost than the full material cost.
Also when offcuts produced by an optimisation are valued, for example on the Management summary, they are valued at a reduced cost (cost reduction).
For each allowance a minimum and maximum value is set as a percentage of the original board cost. For example, and minimum value for cost reduction of 20 would value the offcut at 20% of the original board cost. If the board cost is 50 per square metre the offcut cost is 10.
If the minimum and maximum values are different the minimum value is associated with the smallest offcut and the maximum value is associated with the largest offcut. This allows each offcut to be assigned a value within this range based on its size.
Example
Maximum offcut size: 2440 x 1220 mm
Minimum offcut size: 300 x 200 mm
Board cost 4.25 per square metre
Maximum offcut percentage: 70%
Minimum offcut percentage: 30%
Percentage cost of offcut 1237 x 420 =
Range in square metres = 2.97-0.06
Range in percentage points = 40
Percentage points per square metre = 40/2.91
Square metres in offcut above smallest = 1.237x.42-0.06 = 0.459
Percentage applied to this offcut = 0.459 x 40/2.91 = 6.3
Percentage value of offcut of 1237 x 420 = 30 + 6.3 = 36.3%
Cost per square metre of 1237 x 420 = £4.25 x 36.3/100 = 1.54
For a larger offcut a different percentage applies, for example, for an offcut 1500 x 900 the percentage is:-
1.500 x 0.900 -0.06 x 40/2.91 = 17.73
Percentage value of offcut 1500 x 900 = 30+17.73 = 47.73%
Cost per square metre of 1500 x 900 = £4.25 x 47.73/100 = 2.02
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