RepairFurnitureMedium

Fixing a Loose Chair Rail

A chair joint that has been re-glued twice already and come loose again. The repair that ends it is a bolt right through the leg and rail, so the load stops depending on glue.

Designthe dimensions everything else is derived from

Leg section

40 x 40 mm

Rail section

40 x 25 mm

Bolt grip

65 mm (leg 40 plus rail 25)

Head

countersunk, so it finishes flush in the leg face

Nut

let into the inside face of the rail in a 12 mm recess

Cut list sizes are finished sizes and a chair repair has almost no cut list. The only allowance that matters is the plug: cut it long, glue it in, and pare it flush rather than trying to cut it to length first.

Materialswhat each part is made from, and why

All materials

Beech (American) · the dowel that plugs the recess

Most chairs are beech, and a repair piece in the same timber will move with the chair instead of opening a gap around itself.

Stainless Steel A2 (304) · the bolt, washer and nut

A2 rather than plain steel even indoors: a chair sits on a floor that gets washed, and a rusted bolt in a beech leg stains the timber through the finish.

Cut listfinished sizes, worked back from the design

Part	Qty	Finished size	Stock
Dowel plug	1	12 mm diameter, 15 mm long	Beech (American)

Fastenersquantities and lengths that follow from the joints

All standards

Item	Qty	Grip	Standard
M6 x 80 countersunk socket screw	1	65 mm	DIN 7991
M6 x 80 countersunk socket screw — product grade	alternative	—	ISO 10642
M6 plain washer	2	—	DIN 125 A
M6 nylon-insert nut	1	—	DIN 985

Grip is the sum of the clamped thicknesses. A bolt has to clear the nut by two full threads, which is what sets the length that appears in each row — not a preference.

M6 x 80 countersunk socket screw · grip 65 mm

Countersunk so the head sits flush in the leg and nothing catches on it. Grip is the leg (40) plus the rail (25); add the nut and two washers and 80 mm is the first length that clears. DIN 7991 →

M6 x 80 countersunk socket screw — product grade

The ISO twin of the same screw with the same 90 degree head and the same 1.0 mm pitch. Either designation may be supplied. ISO 10642 →

M6 plain washer

One under the head and one under the nut. Beech is hard but thin, and the washer is what spreads the clamp over the whole rail section. DIN 125 A →

M6 nylon-insert nut

A chair joint is loaded every time somebody leans back or tips on two legs. The insert keeps the bolt from working loose at the same rate the glue did. DIN 985 →

Toolsand what each one is for on this job

All tools

Drill

Boring 6.5 mm clearance through the leg and rail.

Twist Drill Bits

6.5 mm for M6 clearance, plus a 12 mm bit for the recess in the rail and a countersink for the head.

Countersink

Setting the screw head just below the leg face so it can be filled, not just left proud.

Hex Key (Allen Key)

Countersunk socket screws take a hex key; worn keys are what round out the socket on the next repair.

Vernier & Dial Caliper

Confirming the leg and rail sections, since the bolt length depends on both.

Tape Measure

Centring the hole in the rail section; a bolt near an edge will split the rail.

Order of workthe sequence, and where it is not free to change

Clear the old glue out of the joint and dry-fit the rail. If it will not close, the repair has to fix that first.
Glue and clamp as usual. The bolt is not a substitute for a joint that fits.
With the joint still clamped, bore through the leg into the rail.
Take the rail off, enlarge the hole in the rail to 12 mm for the nut recess, and countersink the leg face.
Reassemble with glue, fit the screw, washer and nut, and tighten until it just bites.
Cut a beech dowel, glue it into the recess and the countersink, and pare flush when dry.

Where it goes wrongthe three failures worth designing out

Boring the leg and rail separately. The holes will not line up, and the repair becomes a bigger hole in both parts.
Leaving the screw head proud. On a chair leg it catches on clothing and on the floor when the chair is tipped.
Treating the bolt as a replacement for the joint. A bolt through a gap is a bolt that is bending rather than clamping.

Frequently asked questions

Why a countersunk screw rather than a hex head bolt?

Because it is in a surface. A chair leg is handled, and a hex head standing 6 mm off the face is a snag. The countersunk head finishes flush and can be plugged.

Does the repair show?

On the inside face, no, because the nut sits in a recess closed by a beech plug. On the outside, there is a plug matching the surrounding timber, which is the standard appearance of any repaired chair.

Could the rail be dowelled instead?

Dowelling a joint that has already failed twice in the same place tends to fail a third time, because the holes enlarge with each attempt. A through-bolt engages fresh material at 90 degrees to the old failure.