Step by step
Make parts that press together without glue
Two parts that go together with hand pressure and stay together, with no glue and no fasteners.
Before you start
Anybody making something that has to come apart, or anybody tired of clamping.
- The two parts, drawn.
- A kerf measurement for this material, or five minutes to take one.
Measure the kerf first, everything depends on it
A press fit is a slot slightly narrower than the tab that goes into it. The beam has width, so a slot cut on its drawn line comes out wider than drawn and a tab comes out narrower. Both errors push in the same direction: loose.
Cut a kerf strip once for this material and this thickness. It is the number the rest of this depends on.
Cut the slot to the material, not to the drawing
The slot is made to the thickness you measured on the sheet, adjusted by the kerf. That is why the thickness has to be measured rather than read off the label: sheet sold as 3 mm is often 2.7.
Add corner relief, or it will stand proud
A round beam cannot cut a square inside corner. Left alone, the leftover material in each corner stops the tab before it seats, and the joint stands a millimetre open however hard you push.
Corner relief cuts a small round notch into each corner so the tab can go all the way home. It is nearly invisible and it is the difference between a joint that closes and one that does not.
Every setting, and what it does
10In 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.
Slot length in millimetres
Starts at 20
Slot width in millimetres: material thickness minus kerf
Starts at 3
How many slots in the row
Starts at 1
Spacing between slots in millimetres
Starts at 10
Swell the slot walls so the panel is squeezed, not just held
Starts off
Material thickness in millimetres. The bumps are sized from this.
Starts at 3
Beam width (mm). A bump under half of one is burnt away.
Starts at 0.15
Light comes apart again. Firm goes together once.
One of: Light, Firm
Row left edge (mm)
Starts at 10
Slot top edge (mm)
Starts at 10
How to know it worked
- The parts go together with firm hand pressure and no hammer.
- They stay together when you lift the assembly by one part.
- The joint closes flush, with no gap at the shoulder.
When it goes wrong
4It is loose.
The kerf is set too small or left at zero. Measure it properly.
It will not go in at all.
The kerf is too large, or the thickness is wrong. Check the thickness with calipers first.
It goes most of the way and stops.
The inside corners are round. Turn on corner relief.
It was right yesterday and is loose today.
Different sheet. Thickness varies between sheets of the same nominal size, especially in ply.