The finger joint (tabs and slots)
Tabs and slots — the finger joint, or comb joint — is the corner joint: two parts meeting at an angle, with solids and gaps alternating along the whole edge, like interlaced fingers.
It is the joint of boxes, drawers and frames. It holds far better than a simple butt, because the contact area is large and the load spreads across every tab.
When you want it, and when you do not
- You want it when two parts meet along an edge: two sides of a box, a side and a bottom.
- You also want it when the two parts are on the same plane and must be joined end to end: it is the only joint in Plyjoin that works between coplanar parts, for instance to extend a panel beyond the size of your sheet.
- You do not want it when two parts cross each other: that calls for the cross-lap joint.
How to make it
1. Put the two parts in place with a little overlap: they must intersect along the shared edge, not merely touch. 2. Select them both (⌘/Ctrl+click). 3. Choose “Tabs and slots” and create it.
The joint panel then shows the number of tabs and the length of the contact. The “Flip side” checkbox swaps solids and gaps: useful when two adjacent joints compete for the same corner.
How many tabs
It is the only choice you have to make, and there is a simple rule: a tab must not be narrower than the material is thick. On 4 mm plywood, tabs under 4 mm snap.
| Edge length | Suggested tabs |
|---|---|
| 40 – 60 mm | 3 |
| 60 – 120 mm | 5 |
| 120 – 200 mm | 7 |
| over 200 mm | 9 or more, odd |
An odd number is nearly always better: both ends of the edge stay solid, and the corner is stronger.
If the program says “Too many tabs for the available length”, you are asking for solids and gaps narrower than a fifth of a millimetre: reduce them.
Why they sometimes snap during assembly
Almost always the grain direction: a thin tab cut across the grain breaks as soon as you force it. If you are free to lay parts out, orient them so the tabs run along the grain. And never force a dry 0.1 mm joint: a little warmth or a pass with a file costs less than a broken part.
Try it now
Open the app and make two rectangles at a right angle: two clicks and you have your first finger joint.
Plyjoin works out the joints for you and gives you a DXF ready for the machine. It runs in your browser, with nothing to install.
Try it now