Fitting and Fixing in Carpentry
FIXING INTO CHIPBOARD
Because neither nails nor screws hold well in chipboard, how do you hold a butt joint together? The answer is that you do use screws, but to help them grip, you drive them into a chipboard plug. Chipboard plugs are a bit like ordinary wall plugs.
In fact, you can use ordinary plugs, but you have to be careful to position the plug so that any expanding jaws open across the board’s width and not across the thickness where they could cause the board to break up. The initial stages of the job are exactly the same as for the overlap joint – marking out, drilling the clearance holes, and so on. The difference is that instead of boring pilot holes in the second piece of wood, you drill holes large enough to take the chipboard plugs.
Pop the plugs into the holes, glue the joint together and drive home the screws. Incidentally, if you can’t use any sort of plug at all – for example, when screwing into the face of the chipboard the only way to get the screw to hold properly is to dip it in a little woodworking adhesive before you drive it home.
REINFORCING BLOCKS
The joints described so far are fairly robust, but if a lot of strength is needed it’s worth reinforcing the joint with some sort of block. The simplest is a square piece of timber. First drill and countersink clearance holes through the block and glue and screw it to one of the pieces you want to join so that it’s flush with the end. To complete the joint, glue the second piece in position, and drive screws through into that.
You can arrange for the block to end up inside the angle or outside it. Choose whichever looks best and is easiest to achieve. With the block inside the angle, you’ll have a neat joint and the screw heads won’t be openly on display. However, in most cases it means screwing through a thick piece of wood (the block) into a thin piece (one of the bits you want to join), so it’s not as strong as it might be. If greater strength is needed work the other way round, driving the screws through the pieces to be joined, into the block. You can neaten the result to a certain extent by using a triangular rather than a square block.