How to set kerbstone dimensions so you stop wasting material
The margin on kerbstones is decided in the cutting plan. On the same road, good dimensioning saves one to two tenths of the material; bad dimensioning means paying for the quarry and the saw blade.
Which three variables actually drive the cutting plan?
The largest slab size the block can yield, the length, width and section of each finished piece, and the saw kerf. The first two come from the design, the third from the machine. Put the three together and you know how many pieces come off one slab and how much offcut is left. Without the kerf width you cannot plan at all — so ask the factory for that first.
Why are kerbstones so sensitive to dimensioning?
Because they are long, narrow and deep in section, so material consumption per metre of length is high and offcuts can hardly be reused. Leave 10 cm over on a one-metre kerb and that 10 cm is scrap, permanently. Length should therefore be set against the slab size, not rounded to a road module and left at that.
What if the module and the slab size conflict?
Work out the material consumption both ways: full module lengths, versus optimal slab lengths plus site cutting. Sometimes adjusting how the curve sections are divided lets the whole straight run use the optimal length, and the material saved far exceeds the effort of amending the drawing. Do this with the designer before ordering, not after cutting.
Do chamfers and grooves consume more material?
Yes. A chamfer removes the arris, a groove cuts a channel into the side, and both need allowance beyond the finished dimension. If the quotation says only 100x300 section with no chamfer size and no groove specification, the factory will use whatever default wastes least, and the delivery may not match the drawing.
How much allowance is reasonable?
Too much is direct waste; too little means no conforming piece can be cut. The sensible approach is itemised allowance: length allowance for the number of cuts, section allowance for edge trimming, shaped work allowance for the process. Ask the factory to mark each allowance on the cutting plan and you can see which one is eating material. Visible allowance is negotiable allowance.
How do you check the supplier actually planned it?
Ask for a cutting plan showing slab size, the layout of each piece, the kerf and where the offcuts fall. Anyone who can produce one has usually done the arithmetic; anyone who only promises 5 percent waste verbally made the number up. With the plan you can also compare — give the same plan to two suppliers and the only remaining difference is the processing fee.