The wobbly flat-pack shelf you should stop tightening

Most small fixes are worth doing. A wobbly flat-pack shelf is a good test of that rule, because tightening it feels productive for about a week.

The shelf is made of chipboard, which is wood chips pressed with glue. When a screw goes in and out a few times, the hole gets bigger. Each time you tighten it, the fix lasts a little less. The shelf wobbles again, and you tighten it again.

Why it keeps coming loose

Flat-pack furniture is built to be put together once. The screws and the cam locks (the round metal discs that clamp the pieces) grip chipboard rather than solid wood. That grip is weak when the board is damp, overloaded or moved around.

The back panel is usually thin fibreboard held with small nails. It is what stops the whole frame going into a diamond shape. If the nails have pulled out, the shelf will wobble however hard you turn the screws.

What is worth doing

Try these before you give up.

• Check the back panel. Press the nails back in, or add a few small new ones. A stiff back often cures most of the wobble.
• Tighten the cam locks once, by hand, in order.
• Level the floor contact. Fold a bit of card under one foot if the floor is uneven.
• Take weight off the top shelf. Heavy loads high up make the whole unit rock.
• Fix it to the wall. Wall straps keep a tall shelf from tipping, which is also a safety matter in homes with children or pets. Use the right anchors for your wall type and follow the instructions that came with the strap.

When to stop

Stop when you see any of these.

• The screw holes are stripped and the screw spins without gripping.
• The chipboard is swollen, crumbling or soft at the edges, which can happen after damp or a leak.
• The panels have split.
• The shelf has been taken apart and put back together more than once.

At that point it is cheaper in time and temper to replace it. Do not keep adding bigger screws. They split the chipboard further. Wood glue and dowels can rescue a shelf that is otherwise sound, but not one that is crumbling.

What it says about small fixes

Most home fixes follow the same pattern as the shelf. There is a cheap first attempt that nearly always works, a second attempt that sometimes works, and a point where more effort loses to a replacement. The skill is knowing which stage you are at.

For the shelf, the first attempt is the back panel and the cam locks. The second is a dab of wood glue in the loose holes, left to dry overnight. After that, you are repairing something that was never built to be repaired.

It helps to ask two plain questions. How long will this last if I fix it? How long did it take the last time? If the answers are one week and an hour, the fix is not paying for itself.

A shelf that holds light books and sits against a wall is a different case from a tall unit full of heavy things in a house with children. In the first case, living with a slight lean is fine. In the second, replace it or secure it, because a falling shelf is a risk, not an annoyance.

The rule

If you have tightened it twice and it wobbles again, stop. Use the shelf only for light things, and fix it to the wall if it is tall. If it is stripped and swollen, replace it, and when you do, anchor the new one to the wall from the start.

For another small repair with a clear point to stop, see the pan you should stop scrubbing. For a quick job that does work, stop a door squeaking takes two minutes.