How cutting optimisation reduces aluminium waste

Every bar of extrusion you buy is cut into the lengths a job needs, and whatever is left over goes to the rack or the scrap bin. How much ends up in the bin depends less on the saw operator than on the cutting list they were handed. This article is about that list: where the offcuts come from, how an optimised cutting list reduces them, and what to keep an eye on afterwards.

Why offcuts happen

Offcuts are the gap between the lengths you buy and the lengths you use. A supplier sells bars in a handful of stock lengths. A job needs heads, sills, jambs and mullions in whatever sizes the openings happen to be. Unless those sizes divide neatly into the bar, each bar ends with a piece that is too short for the next cut.

Three habits make it worse:

• Cutting in list order. Taking the cuts as they appear on the sheet, one after another, means each bar is started fresh for whatever cut happens to be next.
• One bar length for everything. The longest stock length feels safe, but a long bar and a short cut leave a long remainder.
• Nobody owns the offcut rack. Remnants go on the rack, nobody knows what is there, and the next job starts from a full bar anyway.

Optimising a cutting list into stock lengths

An optimised cutting list looks at every cut of a profile at once and works out which cuts belong on the same bar. Long cuts are paired with short ones, similar lengths are grouped, and the sheet tells the operator exactly which pieces come out of which bar and what is left at the end of each. The saw operator follows the sheet instead of solving the puzzle at the bench.

The difference shows on the sheet before a single cut is made: the number of bars the job needs, the leftover from each, and which of those leftovers are long enough to keep. In Alumetric, the special cutting sheet can be sorted by length or optimised into stock lengths for the profiles you choose, so you can compare a job both ways.

Cutting across jobs, not one at a time

The optimiser has more to work with when it has more cuts to choose from. Two jobs that use the same profile in the same colour will usually pack into fewer bars together than apart, because a short cut from one job can fill the end of a bar from the other. The conditions are practical ones:

• Same profile and the same finish, so the pieces are interchangeable.
• Fabrication dates close enough that neither job waits on the other.
• Labels on the cut pieces so the two jobs do not get mixed at the bench.

If you cut for several jobs a week, a standing habit of batching by profile and colour is worth more than any single clever cutting plan.

Keeping an offcut rack that gets used

A remnant is only worth keeping if someone will find it and use it. That takes a small amount of discipline:

• Label as you cut. Profile code, length and colour, written on the piece before it leaves the saw.
• Set a minimum length. Decide the shortest piece worth keeping for each profile and scrap anything below it, so the rack holds useful stock rather than clutter.
• Use the oldest first. A rack that only ever grows is a scrap bin with extra steps.
• Check the rack before ordering. When the cutting list for the next job is ready, look for cuts that an existing remnant already covers.

What to measure

You do not need figures from anyone else. Two numbers from your own workshop tell you whether the changes are working: the metres of each profile you bought in a month, and the metres you actually cut into parts. The closer those two numbers are, the less you are paying for aluminium that never becomes a window. Track them per profile, because a frame profile and a bead profile behave very differently, and watch the trend rather than any single month.

The optimised cutting sheet gives you a third number: the bars a job would need if every cut packed perfectly. Comparing that with the bars you ordered shows how much of the gap is the cutting plan and how much is the order.

Where to start

Pick the profile you buy the most of. Run one job's cutting list through the optimiser, cut it that way, and keep the remnants on a labelled rack for a month. That single profile will show you whether the habit is worth extending to the rest, and the cutting sheets and other documents Alumetric produces are built to make the comparison easy.