Cut size

The door of this cabinet is seven hundred and sixteen millimetres high. Yet on the saw it isn't cut at seven hundred and sixteen, but at seven hundred and twelve. In this lesson you'll see why: how much the saw blade takes away, what the trim is, how you get from the finished size to the cut size, and what the edge bander does to the size.

0:24The saw kerf

A saw blade doesn't cut like a knife: it takes away a strip of board as wide as the teeth of the blade. That strip is called the saw kerf, and it ends up as sawdust. How wide it is depends on the blade, and it's usually a few millimetres.

If you mark out two parts of four hundred millimetres side by side on an eight hundred millimetre strip and cut on the line, you don't get two whole parts. The cut between them eats its own strip, so one part is shorter by the width of the kerf.

That's why the size on the saw is set from the blade to the fence. The part that's cut to size is between the blade and the fence, and the kerf falls on the offcut side. So every part is accurate, however many cuts came before it.

1:08The trim

We talked about the trim in the lesson on particleboard. The factory edges of a sheet aren't always straight or clean, so a narrow strip is cut off each of the four edges first. The parts are laid out only inside the trim.

With a ten millimetre trim, a sheet of two thousand eight hundred by two thousand and seventy has two thousand seven hundred and eighty by two thousand and fifty of usable board. How much trim you need depends on the board and on the saw.

1:38Finished size and cut size

The finished size is the size of the part with its edge tape, as it will be in the cabinet. Edge tape has its own thickness, so the board is cut smaller, by the thickness of the edge tape on each edge that gets it. That's the cut size.

A door with a finished size of seven hundred and sixteen by three hundred and ninety-six millimetres gets two millimetre edge tape on all four edges. Across the height there are two edges, top and bottom, so the cut size is four millimetres smaller: seven hundred and twelve. The same goes for the width: three hundred and ninety-two.

The rule is always the same: from the finished size, take off the edge tape on both edges of that size.

2:21Edge tape on some edges only

Not every part gets edge tape on all four edges. If only the two longer edges have it, only the shorter size gets smaller. The same door with edge tape on its longer edges only is cut at seven hundred and sixteen by three hundred and ninety-two. An edge without edge tape is cut to the finished size.

Thin edge tape gives decimals. A shelf of five hundred and sixty-four millimetres, with zero point four millimetre edge tape on both shorter edges, is cut at five hundred and sixty-three point two. If your saw cuts to the whole millimetre, round the way you usually do, but the same way on every part.

Remember: edge tape on the longer edges shortens the shorter size, and edge tape on the shorter edges shortens the longer one.

3:07Pre-milling

Many edge banders mill a thin layer off the edge before the edge tape goes on, so that the edge is straight and clean. That's pre-milling. It makes the part a little smaller again, so this allowance is added to the cut size. How much it takes off depends on the machine, and there's more about edge banders in the Edge banding module.

When you order cutting and edge banding from a panel supplier, agree whether your list gives finished sizes or cut sizes. If you send cut sizes and the supplier takes the edge tape off again, every part comes out smaller by the thickness of the edge tape.

3:43In short

In short. Every cut takes away a strip of board as wide as the saw kerf, so the size on the saw is set from the blade to the fence. Before cutting, a trim is cut off each edge of the sheet, for example ten millimetres. The finished size is the size of the part with its edge tape, and the cut size is the finished size minus the edge tape on each banded edge. A door of seven hundred and sixteen by three hundred and ninety-six, with two millimetre edge tape all round, is cut at seven hundred and twelve by three hundred and ninety-two. Edge tape on the longer edges shortens the shorter size, and on the shorter edges the longer one. Pre-milling needs an allowance that depends on the machine. And agree with your panel supplier which sizes are on the list.

In Easy Form Studio you enter sizes as finished sizes, the way they will be in the cabinet. The edge tape is taken off only in the cutting list, and there each part has both its cut size and its finished size.

You set the edge tape for each edge separately, in the EFS Board tab, in the Edging Tape box. Set an edge without edge tape to None, and that edge is cut to the finished size. The program doesn't add a pre-milling allowance, so agree on it with whoever does the banding.

The trim is entered with the sheet size, in the price list on the Sheets worksheet; the default is ten millimetres. The saw kerf is in the export settings.

The tutorials Cutting list and cut size, and Nesting and board prices, show the whole process step by step.

A three-question quiz and the summary are on the academy page, the link is below the video. In the next lesson: the cutting list, how to read it and how to sort it.