Why will my cam lock not tighten, and how do I fix a spinning one?

The joint has two parts doing two different jobs. The dowel locates the panels and holds almost nothing. The cam is the entire clamping force of the joint: a half turn rotates an internal spiral that grips the neck of the bolt head and drags it in. When a cam will not tighten, one of those two components is not where it thinks it is.

What you'll need

• Screwdriver that properly fits the cam slot
• Replacement cams and bolts, sold cheaply in packs (optional)
• Hardwood dowel and wood glue, for a stripped hole (optional)
• 15mm flat bit or Forstner bit, for re-drilling (optional)
• Two-part epoxy or a chipboard repair filler (optional)

Step by step

1. Check which way the cam is facing.A cam has an opening in its side that the bolt head must enter. If it went into its hole with the opening facing the wrong way, it can be turned all day and never meet the bolt. Lift it out and refit with the opening pointing at the bolt hole.
2. Check the bolt is screwed fully home.The threaded bolt screws into a pre-drilled hole in the mating panel and should sit down to its shoulder. Half a turn short and the head sits too far out for the spiral to reach it.
3. Turn clockwise, and only half a turn.The stop is real. A cam that has been forced past its stop has cut a groove in the soft chipboard and will never grip again.
4. Feel for what the resistance is doing.Firm resistance that builds and then stops is correct. No resistance at all means the spiral is not on the bolt, or the hole is chewed out. Resistance that suddenly goes slack means it has just stripped.
5. Look at the joint line while you turn it.A working cam visibly closes the gap. If the gap does not move, the cam is not engaged with the bolt, whatever the cam is doing.
6. For a stripped hole: pack it and start again.Drill or chisel the damaged 15mm hole out cleanly, glue in a tightly-fitted hardwood dowel or a plug cut from an offcut, let it cure fully, then re-drill a fresh 15mm hole in the same place to the original depth. This gives solid material for a new cam to bite into.
7. Or move the fixing rather than repairing it.Where the panel allows, drill a new cam hole 30 to 40mm along from the failed one and a matching bolt hole in the mating panel. Often quicker than a plug repair and just as strong.
8. Or convert the joint to a screw.On a hidden joint, a 4 x 50mm screw through the side panel into the edge of the mating panel, with a pilot hole to stop the chipboard splitting, does the same job permanently. It is not reversible, so keep it for units that are staying put.
9. Retighten the rest of the carcass once one has been repaired.A joint that stripped was probably carrying more than its share because its neighbours were slack. Go round the lot with a half turn each.

Tips

• Buy a pack of assorted cams and bolts before you start dismantling anything — they are pennies, and the missing or damaged one always turns up at the wrong moment.
• A cam turned with a badly-fitting screwdriver rounds its slot out and then cannot be turned at all. Use the widest blade that sits properly in the slot.
• Mark the cams you have tightened with a pencil dot as you go round a big unit. It is the only way to be sure none was missed.

Common mistakes

• Turning a cam past its stop to make the joint tighter — The spiral cuts a groove in the chipboard. From that point the cam turns freely and the joint can never be pulled tight again.
• Assuming the dowel provides strength — It locates the panels and nothing more. If the cams are slack, the carcass is slack, however tight the dowels look.
• Hammering panels together to close a gap the cam should close — It splits the board around the dowel holes and leaves the joint slack anyway. The cam is what pulls it together.

If it doesn't work

Questions people ask