Plywood sheet nesting
Nesting places rectangular parts on a sheet so you can read the waste before you buy the board. A small change to one part size can change the whole layout, which is why it pays to run the layout rather than guess.
The job
Stock is one 2440 × 1220 mm sheet, the common 8 × 4 ft plywood size. Kerf is 3 mm, the gap a typical panel saw or track saw blade leaves. Trim is 10 mm on each edge, so the usable rectangle is 2420 × 1200 mm.
Rotation is allowed, and the layout is guillotine: every cut runs straight across the piece it is cutting, the way a panel saw works.
| Part | Width (mm) | Height (mm) | Qty |
|---|---|---|---|
| Door | 600 | 800 | 4 |
| Shelf | 560 | 300 | 4 |
The layout
CutGrid places 8 of 8 parts on 1 sheet. Part area is 2,592,000 mm² and the sheet is 2,976,800 mm², so 87.1% of the board becomes parts. The other 12.9% is kerf, trim and the offcut that stays on the sheet.
Waste here means everything on the bought sheet that is not a finished part. It is not a theoretical figure from a research paper on packing; it is what the plan in the drawing leaves behind.
Layout produced by CutGrid’s optimizer for this example. Coloured blocks are parts, dashed areas are offcuts, and the outer band is trim.
- Door
- Shelf
Ten millimetres wider
Change the doors from 600 to 610 mm wide and keep everything else. The part area barely moves, from 0.87 to 0.88 sheets, but the layout now needs 2 sheets and waste rises to 55.9%.
Four doors at 600 mm plus three kerfs are 2409 mm, which fits in the 2420 mm usable width. At 610 mm they are 2449 mm, which does not, and turned on their side two doors are too tall to stack inside 1200 mm. The doors can no longer sit in one row.
This is why you run the layout every time a size changes. An area estimate would still say one sheet.
Layout produced by CutGrid’s optimizer for this example. Coloured blocks are parts, dashed areas are offcuts, and the outer band is trim.
- Door
- Shelf
Reading the plan before you cut
Check three things on the drawing: that every part is placed, which offcut is large enough to keep, and the cut order. On a guillotine plan the first cuts split the sheet into strips and the later cuts divide each strip. CutGrid’s PDF lists that cut sequence sheet by sheet.
Common mistakes
Sizing parts to the full sheet
A 2440 mm sheet does not give four 610 mm parts once a blade and a trim are involved. Size parts to the usable rectangle: the sheet minus trim on both sides, minus one kerf per gap.
Turning off rotation for every part
Rotation lets the layout turn a part 90°. Turn it off only for parts whose grain or pattern must run one way; the grain direction guide shows how.
Trusting nominal sheet sizes
Measure the board. Some sheets sold as 8 × 4 ft are 2440 × 1220 mm and others 2438 × 1219 mm, and a millimetre per part adds up across a row.
Questions
- What is the standard plywood sheet size?
- 2440 × 1220 mm (8 × 4 ft) is the most common. Larger sizes such as 2500 × 1250 mm and 3050 × 1525 mm exist depending on the product and region. Use the size your supplier actually stocks.
- Does CutGrid find the best layout?
- It searches many layouts and keeps the one with the fewest sheets, then the least waste. When the result equals the lower bound, the app marks it as the fewest sheets possible. This example is marked that way.
- What kerf should I use?
- The blade’s actual cut width. Most panel saw and track saw blades cut 2.5 to 3.5 mm; measure a test cut with calipers if you need to be exact.