Step by step
Make a box that fits together
A finished box, cut from one sheet, that presses together and stays square without clamps.
Before you start
Anybody who has cut a flat part and not yet cut something that assembles.
- A sheet of ply, MDF or acrylic, any size, with room for six panels.
- A pair of calipers, or a ruler you trust to a tenth of a millimetre.
- Ten minutes, most of which is the cutting.
Measure the material, do not read the label
Sheet sold as 3 mm is rarely 3 mm. Ply moves with the weather and comes off the saw a little under or a little over. Two tenths of a millimetre is enough to turn a joint that presses together into one that falls apart or one that will not go.
Measure the actual sheet you are about to cut, in three places, and use the smallest reading. Everything else in this tutorial is built on that number.
Say how big, and say which big you mean
Type the width, the depth and the height. Then answer the question underneath them, which is the one that catches everybody: are those numbers the outside of the box, or the space inside it?
They are two different boxes. On 3 mm material an inside measurement makes a box 6 mm bigger in each direction, because there is a wall on each side. Pick Inside when the box has to fit around something. Pick Outside when it has to fit into something.
Choose the teeth
The joint is a row of teeth cut into each edge, so the two panels lace together. Finger size is how long one tooth is along the edge.
Somewhere around three times the material thickness is a good starting point: 9 mm teeth on 3 mm ply. Much smaller and the teeth are fragile and the edge looks busy. Much larger and there are only two or three per edge, which holds less well and looks like a mistake rather than a joint.
Tell it the beam width
The beam removes material as it cuts, so every tooth comes out slightly narrower than drawn and every slot slightly wider. Left at zero, the box assembles loose and rocks.
Cut a kerf test strip once for this material and this thickness, put the measurement in, and the generator grows the panels by half a kerf and shrinks the slots by one. The joint then closes up with hand pressure and stays.
If you have never measured it, 0.15 mm is a reasonable first guess for a CO2 machine on thin ply. Measure it properly before you cut anything that matters.
Decide about the lid
Closed gives six panels and a box you glue shut, which is right for something that is never opened again. Open top gives five, for a tray or a planter or anything you reach into.
Sliding cuts a groove in the walls and a panel that runs in it, so the box opens and closes with no hinge, no catch and nothing to buy.
Cut it, and check one joint before you cut them all
The generator lays every panel flat on the sheet with the joints already cut. Send it, and when it comes off the bed push two panels together before you assemble the rest.
It should need firm hand pressure and no hammer. Too loose and your kerf number is too small. Too tight and it is too large. Change it by half a tenth and cut one corner again, not the whole box.
Every setting, and what it does
13In the order you meet them. The second line on each is what goes wrong when it is set badly, which is usually the more useful half.
The three sizes of the box, in millimetres.
Getting these right and Measure wrong makes a box the right shape and the wrong size.
Whether those three numbers are the outside of the box or the space inside it.
The single most common reason a finished box does not fit what it was made for.
The measured thickness of your sheet.
Every joint in the box is cut to this. Wrong here and nothing fits, however good the rest is.
How long one tooth is along the edge. Around three times the thickness.
Too small and the teeth snap; too large and there are too few to hold.
How many teeth that edge is divided into. 1 is normal.
Higher looks finer and takes longer to cut. It does not change the strength much.
The width of your beam. Panels grow half of it, slots shrink one.
Left at zero, the box rattles. Set too high, the panels will not go together.
Closed, open top, or a lid that slides in a groove.
Sliding needs a little more height, because the groove takes some of the wall.
A small round notch in each inside corner.
Without it a square tab bottoms out on the rounded corner the beam leaves, and stands proud.
Bolts the corners with a captive nut, in M3, M4 or M5.
Choose this when the box has to come apart again. It is the only option here that is not glue.
Splits the inside into equal compartments.
The compartments are always equal. For unequal ones, draw the dividers yourself.
A lift-out tray inside the box, at a height you set as a percentage.
Only on an open or sliding lid. There is nowhere to lift it out of a closed box.
Raises the floor so the box stands on its walls rather than on its base.
Useful when the base would otherwise be the part that scuffs the table.
The sheet the panels are laid out on.
Set it to your real stock so the layout does not run off the material.
How to know it worked
- Two panels press together with hand pressure and do not fall apart when you let go.
- The assembled box sits flat on a table without rocking.
- The outside measurement is what you asked for, if you chose Outside.
When it goes wrong
4The joints are loose and the box rattles.
Your kerf number is too small, or zero. Measure it with a kerf test strip and put the real figure in.
The panels will not go together at all.
Either the kerf is set too high, or the thickness is wrong. Check the thickness with calipers first, because it is the more common of the two.
The tabs stand proud instead of sitting flush.
The inside corners are rounded, because a round beam cannot cut a square corner. Turn on corner relief.
The box is 6 mm bigger than I asked for.
You measured Inside and expected Outside. On 3 mm material that is exactly one wall on each side.