Cutting settings are the difference between a theoretical plan and one the operator can cut exactly. Four things matter: the blade width, trimming of the factory edges, pre-milling of edge-banded parts and the physical limits of the machine. We take them one by one, with usual values and worked examples, then see how to enter them in OptimCut.
What blade width (saw kerf) is
The blade width, also called the saw kerf, is the width of the cut the blade makes. It is not the thickness of the blade body but the width of the teeth, which are slightly wider than the body so they do not bind in the material. Everything inside this width turns into dust.
On panel saws, the usual values are between 3 and 4.5 mm. You will find the exact value marked on the blade or in its data sheet. If you are not sure, make a test cut and measure it with a caliper.
Why the kerf must be included in the plan
Every cut uses one blade width. When you place several parts in a row, the loss is multiplied by the number of cuts. A plan that ignores this assumes the parts sit right against each other, which never happens in the workshop.
Example: four parts along the length of the board
Chipboard panel 2800 × 2070 mm, trimmed 10 mm on each side: usable area 2780 × 2050 mm.
You want 4 parts of 695 mm along the length. Without the kerf: 4 × 695 = 2780 mm. It looks like they fit exactly.
Between 4 parts there are 3 cuts. With a 4 mm blade: 3 × 4 = 12 mm used up.
Real requirement: 2780 + 12 = 2792 mm, which is 12 mm more than the usable length.
Result in the workshop: the fourth part comes out at 2780 − 3 × 695 − 12 = 683 mm, so it has to be cut again.
Across the width of the board, the same logic applies. If you cut 5 strips of 400 mm from 2050 mm of usable width, you need 5 cuts (the last one separates the strip from the offcut): 5 × 400 + 5 × 4 = 2020 mm. A 30 mm strip is left. With a 4.4 mm blade, the kerf loss becomes 22 mm and the remaining strip drops to 28 mm.
Simple rule: parts in a row right up to the end of the usable area mean N − 1 cuts; if an offcut is left after the last part, there are N cuts. A cutting optimizer does this calculation for every cut, across the whole board.
Board trimming: why you cut off the factory edges
Trimming means cutting a narrow strip off the edges of the board before starting on the parts. Factory edges are often chipped, have corners knocked during transport, or are not perfectly straight and square. If you start cutting from an unreliable edge, every part that uses it as a reference inherits the error.
The usual values are 10–15 mm on each factory edge. Some workshops trim all 4 sides, others only 2, depending on board quality and the machine. Offcuts already cut in the workshop have clean edges and do not need trimming again.
Example: how much you lose to trimming
Full board: 2800 × 2070 mm = 5.796 m².
Trimming 10 mm on all 4 sides: 2780 × 2050 mm = 5.699 m².
Difference: 5.796 − 5.699 = 0.097 m², about 1.7% of the board.
The percentage is small, but if you leave it out of the plan, parts at the edge come out narrower than the required size.
Pre-milling of edge-banded parts
On edge banders with pre-milling, a cutter removes a thin strip from the edge of the part before gluing, to get a clean, chip-free edge. The cutter usually removes 0.5–1 mm per side. The part must therefore be cut larger by exactly that amount on every banded side.
At the same time, the band thickness (usually 0.4–2 mm) is added to the part size after edge banding. If you enter finished sizes, the cut size on each banded side is:
cut size = finished size − band thickness + pre-milling
Example: a 400 mm part with 2 mm edge banding on both ends
Without pre-milling: 400 − 2 − 2 = 396 mm.
With 1 mm pre-milling per side: 400 − 2 + 1 − 2 + 1 = 398 mm.
If you had cut straight at 400 mm, the part would have come out at 404 mm without pre-milling and at 402 mm with 1 mm pre-milling per side.
More on band thicknesses and how much edge banding to order is in the guide on edge banding calculation for furniture.
Machine limits
A geometrically correct plan can still be impossible to cut on your machine. Three limits matter most often:
- Maximum cutting length. The sliding table or guide of the saw has a limited stroke. A cut longer than the stroke cannot be made in one pass.
- Minimum strip width. A very narrow strip cannot be held safely between the blade and the fence: it vibrates, can break or can be thrown back by the blade. The minimum value depends on the machine and on how the operator works.
- Table size. The board has to fit on the machine table.
You will find the exact values in the machine’s manual and in your own workshop practice. There is no universal value.
Usual values at a glance
| Setting | Usual value | What happens if it is wrong |
|---|---|---|
| Blade width | 3–4.5 mm | The last parts in a row come out undersized |
| Board trimming | 10–15 mm per factory edge | Edge parts come out narrow or with chipped edges |
| Pre-milling | 0.5–1 mm per banded side | The edge-banded part comes out smaller than the finished size |
| Band thickness | 0.4–2 mm | The edge-banded part comes out larger or smaller |
| Maximum cutting length | Depends on the machine | The cut cannot be made in one pass |
| Minimum strip width | Depends on the machine | The strip cannot be held safely against the blade |
How to set it all up in OptimCut
In OptimCut, these settings are applied automatically in the calculation, so the final sizes come out exactly right. The steps are described in detail in the user manual:
- 1Board trimming
At Trim the boards? choose “Yes, trim”, how many mm per side and whether you trim 2 or 4 sides, or “No”. Reusable offcuts from stock are not trimmed again.
- 2Pre-milling
If the optimization contains edge-banded parts, the question Some parts have edge banding. Pre-mill? appears. Choose “Yes, I pre-mill” and how many mm the cutter removes per side; every banded side is cut larger by that amount.
- 3Blade width
In Cutting settings, before starting, check the blade width, along with the method, unit, cycles and minimum reusable offcut.
- 4Edge banding and finished sizes
In Profile & settings, under Edge banding and cut sizes, choose whether the software subtracts the band from finished sizes and which pre-milling it suggests. If you already enter cut sizes, untick Subtract edge banding from the cut size.
What warnings you get
After every optimization, OptimCut checks the plan itself: all parts are on boards, with no overlaps and none sticking out of the board. The result also warns you if:
- the board does not fit on the machine table;
- a cut exceeds the maximum cutting length;
- a strip is too narrow to be held against the blade.
If a part does not fit, the Unplaced parts message appears. One of the causes to check is exactly this: trimming makes the board smaller and the blade uses material on every cut. Resolve the warnings before sending the cut sheet to the workshop.
Do not reduce the blade width or the trimming to fit one more part. The plan looks better, but the parts come out wrong. To learn how to reduce waste properly, read about chipboard cutting waste.
Conclusion
Blade width, trimming, pre-milling and machine limits are a few millimetres that decide whether parts come out to size. Measure them once on your machine, enter them correctly and check them whenever you change tools. The software can do the rest of the calculation.
Try it on a real order with a free Trial account: 3 optimizations per month, up to 100 parts, no card. Details about the Pro plan are on the pricing page.
Frequently asked questions
What blade width should I use for cutting chipboard?
The real width of your blade, marked on the blade or in its data sheet; usual values are between 3 and 4.5 mm. If you are not sure, make a test cut and measure it with a caliper.
How much should I trim off a chipboard panel?
Usually 10–15 mm on each factory edge, enough to remove chipping and get a straight edge. Offcuts already cut in the workshop have clean edges and do not need trimming again.
Do I have to trim all 4 sides?
Not necessarily. It depends on the quality of the factory edges and on your machine; some workshops trim only 2 sides. In OptimCut you choose for every optimization whether you trim 2 or 4 sides and how many mm per side.
What is pre-milling and why does it change the cut size?
Pre-milling is milling the edge of the part just before the edge band is glued on, usually 0.5–1 mm per side. The cutter removes material, so the part must be cut larger by exactly that amount on every banded side.
Why does the last part in a row come out smaller?
Most often because the plan did not include the blade width or the trimming. Every cut uses a few millimetres, and across a row of parts the loss adds up right at the last part.
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