How do I fit shelf support pegs so the shelf sits level?

Shelf pegs — the small pins, studs or spoon supports that carry adjustable shelves in bookcases and kitchen units — look trivial and are the most position-sensitive holes in a piece of furniture. Two millimetres of difference between the front and back hole on one side puts a visible tilt on the shelf, and there is no adjustment to correct it afterwards.

What you'll need

• Shelf supports, and a drill bit matching their diameter
• A drilling jig, a strip of pegboard, or a shop-made template
• A depth stop or a collar for the bit
• Clamps
• A tape measure and a square

Step by step

1. Identify the peg diameter first.5mm is the standard in flat-pack and kitchen furniture; 6mm and 1/4 inch turn up in older and imported pieces. Measure an existing peg rather than assuming.
2. Make or buy a jig.A strip of 5mm pegboard clamped to the panel gives perfectly spaced holes at a fixed distance from the edge. A purpose-made shelf pin jig does the same with a bushing that keeps the bit square.
3. Reference every hole from the same face.Always register the jig against the front edge of the panel, on both sides. Referencing from the back on one side and the front on the other guarantees a tilt if the panel is not exactly to size.
4. Set a depth stop before drilling anything.A collar on the bit, or tape wrapped round it. Through-drilling a cabinet side is a very visible mistake and it happens on the first hole if the depth is not fixed.
5. Drill the front and back holes on one side, then transfer the height accurately.Measure the height from the bottom of the carcase on both sides — not from the top, and not by eye. A carcase is rarely perfectly square, and the bottom is the reference that matters.
6. Keep the bit square to the face.A peg drilled at an angle either will not accept the support or will hold the shelf out of parallel. A drill guide or a jig with a bushing is what keeps it square.
7. Fit the supports and test with the shelf before drilling more.Put the shelf on and check with a level, front to back and side to side. Correct now, before you drill twenty more holes at the same error.
8. Drill extra rows for adjustability while the jig is set up.The whole point of pegs is that shelves move. Drilling the full column now takes minutes; doing it later means re-registering the jig on a built cabinet.
9. Repair a worn hole rather than moving the shelf.Glue a hardwood dowel or a plug into the enlarged hole, let it cure, trim flush and redrill at the correct size. In chipboard, a little PVA and a matchstick is a short-term fix at best.

Tips

• Spoon-shaped supports carry more than plain pins and are worth using for heavy shelves. Some types also take a small screw up into the shelf, which stops it lifting.
• For a shelf carrying real weight, pegs alone at four corners are not much support. A shelf that will hold books wants either a thicker board, a front lip, or a centre support.
• If a shelf rocks, check the pegs before blaming the shelf. One peg not fully seated is the usual answer.

Common mistakes

• Measuring each hole individually with a tape — Human error of a millimetre or two per hole is unavoidable, and it shows as a tilted shelf. A jig removes the measurement from the process entirely.
• Drilling with no depth stop — The bit goes through the side of the cabinet, which on a visible end panel is a permanent and obvious mistake.