Packing Gland

A recess around the shaft, deep enough for several rings of packing.

1. From 40 mm aluminium round bar, cut a body 60 mm long.
2. Bore it through at 16.0 mm as the shaft clearance.
3. From one end, counterbore to 24 mm diameter and 30 mm deep — this is the stuffing box.
4. Cut a shoulder at the bottom of the box, square to the bore.
5. Drill and tap two M6 holes in the end face, 180 degrees apart, for the gland studs.

Modern build spec (derived). A 4 mm annular gap between a 16 mm shaft and a 24 mm box takes standard 4 mm square packing cord. Packing is sold by section size, so the gap decides what you can buy — design the box around the cord, not the other way round.

Rings, not a spiral, and each joint turned away from the last.

1. Wrap the packing cord round the shaft itself and cut it to make a closed ring with a clean butt joint.
2. Cut four rings this way.
3. Fit them one at a time, seating each fully before adding the next.
4. Rotate each ring 90 degrees relative to the one below so the four joints are spread around the shaft.

Why stagger. Every butt joint is a small leak path. Line four of them up and you have made a channel straight through the packing. Spread at 90 degrees, each joint is blocked by solid packing above and below it.

The follower is a loose ring that pushes the packing; the studs pull it in.

1. Turn a follower ring: 23.6 mm outside, 16.4 mm bore, 20 mm long.
2. Drill two slots or ears in its flange to clear the studs.
3. Fit two M6 × 60 studs into the tapped holes from step 1.
4. Retain the follower with M6 flat washers × 2 and M6 hex nuts × 2.
5. Check the follower slides freely in the box with no rock.

The follower clearances matter in both directions. Too tight on the shaft and the follower itself rubs, which is a bearing you did not intend. Too loose in the box and packing extrudes up past it as you tighten. A few tenths of clearance on each side is right.

Two competing measurements, and the right answer is between them.

1. Fill the body with water and turn the shaft by hand, nuts finger tight.
2. Tighten each nut a flat at a time, and after each step count drips per minute AND measure the torque needed to turn the shaft.
3. Tabulate: nut position, drips per minute, turning torque.
4. Keep going until it stops dripping entirely.
5. Now back off until it drips again, and feel the shaft after a minute of turning.

Packed glands are ancient by industrial standards and were universal on steam engines, pumps, valves and marine sterntubes. Materials tell the story of the technology: flax and tallow, then asbestos and graphite, and today PTFE, graphite fibre and aramid. The geometry has not changed at all — only what the rings are made of.

The deliberate leak is the design, not a defect. The packing rubs on a turning shaft and that contact makes heat; the small flow of process fluid past the packing carries the heat away and lubricates the interface. Remove the flow and you remove the cooling. A maintenance culture that treats every drip as a fault destroys glands routinely, which is why the instruction on a pump is to adjust to a drip rate rather than to dryness.

Against its siblings: an O-ring seals statically and completely but cannot tolerate a rotating shaft for long. A lip seal handles rotation with almost no leakage but cannot be adjusted and must be replaced when worn. A mechanical face seal is dry and tight but costs far more and fails suddenly rather than gradually. The packing gland is the only one that can be nursed along by hand, adjusted while running, and repacked with a few pence of cord — which is exactly why it survives on ships and in waterworks where the alternative is a shutdown.

The honest failure mode: packing wears the shaft. A gland run for years will cut a groove where the packing sits, and once grooved, no adjustment seals it. The traditional answer is a renewable shaft sleeve — a sacrificial part, exactly like the shear pin, chosen so the cheap thing wears instead of the expensive one.