Wood moves most across the grain when environmental changes cause a change in relative humidity. A table top or, in this case, a desk top, must be allowed to move when environmental changes take place; if movement is restricted, cracking can result, and often does. Two common ways to allow movement of a large chunk of wood such as a desk top are buttons, and figure 8s.
Two days ago I was preparing the figure 8s to attach the desk top — I did not like the idea of drilling into the aprons to screw the figure 8s. If mounted on the aprons, it would be difficult to screw them to the top, as they would be too close to the inside of the apron walls. I decided to attach blocks to the aprons, and to mount the figure 8s in recesses in the blocks; Forstner bits are great to drill the recesses. This effectively moved the figure 8s away from the apron wall at least one inch:
With the desk top in place, this is what is visible at the back wall:
I had imagined the following situation many times, even in my sleep:
I have to fess up: I have NO idea where the short Phillips driver in the next photo came from. I just found it in the case. But it sure came in handy to allow use of the Bosch PS-10 in tight quarters (you can read about the PS-10 in an article I wrote almost two years ago):
Ah, the magic…
It was not magic, but good planning allowed me to spend less than 30 minutes screwing the figure 8s into the top. Here is how I did it:
- Position the figure 8s on the recesses in the blocks, and screw them semi-tightly, so they won’t rotate or move easily.
- Place the desk top on the base, measure all overhangs, and remember them.
- Using a fat maker, mark dots on the underside of the desk top using the holes in the figure 8s.
- Take off the top, and place it on the workbench upside down.
- Use an egg beater drill with a suitable drill bit and pre-drill the holes for the screws.
- Test at least one hole, to ensure relatively easy entry of the screws.
- Loosen the figure 8s slightly, until they move under slight pressure.
- Place the top back on the base, registering opposite (drilled) corner holes with their respective figure 8 holes.
- Proceed to attach the top to the base using the figure 8s.
It really is that simple. Try it sometime. Another (free!) tip from Sandal Woods!
— Al Navas