Frame No. 21 · C&TR pattern of 1897

Thirty-two spaces, sixteen levers, one argument.

The frame was supplied with thirty-two levers for a junction that was busier than it ever became. Sixteen are connected today; the rest stand white, and the numbering has never been closed up, because renumbering a frame means re-cutting the locking.

§ 01 — THE ROLL OF LEVERS

What each lever works.

Every lever carries an enamelled plate at eye level with its number, its colour and its job. This is that set of plates, read left to right along the frame.

N°	Plate	What it does
1	Down Home Red / stop signal	Protects the junction against a Down train running in from Thrushmoor Bank.
2	Down Distant Amber / distant signal	Cannot be cleared until every stop signal in advance of it is already off. Last off, first back.
3	Spare White / spare	Left in the frame when the Down Goods Loop was lifted in 1962. The numbering was never closed up.
4	Points 4 — Quarry Branch junction Black / points	Normal for the Down Main, reverse for the Quarry Branch. Facing points, so they carry a lock.
5	Facing point lock on 4 Blue / facing point lock	Drives a bolt through the stretcher bar so the blades cannot creep under a train. Reverse to bolt, whichever way 4 is lying.
6	Points 6 — crossover Black / points	Down Main to Up Main, used for engine movements and for the Sunday engineer possessions.
7	Down Main Starting Red / stop signal	Sends a Down train on towards Calderfoot over the main leg of 4.
8	Quarry Branch Starting Red / stop signal	Sends a Down train up the branch over the reverse leg of 4. Cannot stand off at the same time as 7.
9	Up Home Red / stop signal	Reads in from Calderfoot. Opposed to 1, so the two can never be off together.
10	Up Distant Amber / distant signal	The Up counterpart of 2, and bound by the same rule about the signals in advance of it.
11	Spare White / spare	Was the Up Goods Loop home until 1962. Nothing is connected to it now.
12	Up Starting Red / stop signal	Sends an Up train away towards Thrushmoor Bank, clear of the crossover.
13	Gate lock — Hollowgate Lane Brown / gate lever	Bolts the gates where they stand. Every running signal in the frame waits on this lever.
14	Gate stop lock Brown / gate lever	Frees the gate wheel so the gates can be swung off the railway and across the road.
15	Points 15 — goods shed siding Black / points	Trailing points off the Up Main into the goods shed. Locked by 12 while an Up train is signalled away.
16	Spare White / spare	Cut out when the water column was removed. Painted white and left standing.

§ 02 — THE LOCKING

A notch, a bar, and a piece of steel that says no.

Nothing in the tray under the frame is electrical, and nothing in it is clever. It is a set of flat bars that can only slide when the notches line up.

Each lever drives a flat steel tappet down through the tray. The locking bars that serve other levers run across them. A bar can only slide if every tappet it crosses is showing it a notch — and a lever can only move if the bars around its own tappet have somewhere to go.

The consequence is the whole of railway safety as it was understood in 1897, and it is still the reason a mechanical box is trusted: the signalman is not asked to remember which combinations are dangerous. The combinations that are dangerous simply cannot be made. A wrong route is not an error that gets caught. It is a movement that does not happen.

It also explains the one thing visitors find strangest. You cannot put a lever back whenever you like. If lever 2 is off, then 7 is trapped reverse, because 2 was only allowed off on the strength of 7 being off first. The frame unwinds in the reverse of the order it was wound up, and it will wait all day.

Locking tray: Original, 1897. Re-bushed 2009.
Bars: 24 locking bars, 61 dogs
Lever pitch: 5½ inches
Pull: 40–70 lb at the catch handle

Proved against the table below on every open day since 2004.

§ 03 — THE LOCKING TABLE

The same relationship, written down twice.

Read a row across. Holds is what this lever pins where it stands the moment it is pulled — and, read the other way, what has to be standing that way before it will move at all. Both is a bolt, which holds in either direction and is not held back. Held by is whoever is sitting on this lever now.

N°	Works	Holds	Held by

A frame is only as good as this document, which is why we draw one for every box we overhaul and then prove it lever by lever before we sign it off. An undocumented frame is not a safe frame, however well it is greased.

§ 04 — FOR OTHER BOXES

We will come and look at yours.

Eleven frames since 2011, from a six-lever ground frame in Shropshire to a forty-four-lever box in Caithness. Survey first, always — we have never yet quoted for a frame we had not knelt under.

Ask about a survey

Survey: Two days on site, drawings and a condition report
Strip and re-bush: In our shop at Thrushmoor, six to fourteen weeks
Locking: Re-cut to a table we draw and prove with you
Handover: Two days training for your own duty staff