A Note on the C.R.O.
CU 1971 Contents Page Next:
Research Group Report

Cambridge Underground 1971 pp 19-22


With 1970 came the Club's 21st Birthday, but this was not the only feat of longevity to arouse interest and discussion; the pencil rung ladder was now at the ripe old age of 5 years (or even more). It was time to pension the 110 ft. of it off and build a new standard-size ladder. The long vac. term seemed a nice time to do this, and 200 ft. a nice amount to make, with a cost of around £30.

There was nowhere near this amount in the kitty, so last March a Tackle Appeal Fund was launched, which raised £16 from members before the novelty of giving away money wore off. With a grant of £20 from the University's Societies Syndicate we were able to send off for all the material. We intended to use again the ferrule method of fixing the rungs, but South Wales Caving Club could no longer supply us with the ferrules and, unable to find any other source, we decided on the taper-pin method - if it proved strong enough.

July duly came and saw various C.U.C.C. members assembled in Cambridge mainly on the £1-a-day, L.E.A. way, two of us on C.U.C.C. expense accounts. We were given space in the Engineering Department workshops and work began.

Sawing the rungs up took a morning or so, but drilling them, about a day and a half - an inordinately long time, which our President and guest house-keeper, John Lees, attributed to the absence of his customary "idiot 14 year old" companions. The wire was cut up by the C.U.C.C. Wire Cutting Machine, referred to elsewhere as "this formidable apparatus". Formidable indeed; 70 lbs. of A.C. transformer, electricity fed in at 240 volts and reappearing at 100 amps in two pincers attached to the machine by enormous copper wires with minds of their own. Needless to say, no-one was in a hurry to try it out. Luckily a request to have the thing checked for safety led to one of the Workshop Staff putting a new lead and plug on it, tidying up the loose bits and, best of all, having the first go. The pincers gripped the wire about 1½" apart, switch on, and, with a glow, a brightly coloured flame, then smoke galore - two ends of wire. Dabbing them together a bit produces two pointed ends just right for threading rungs.

The only problem remaining was to find out the strength of the taper-pin method of fixing the rungs. This involves driving a tapered mild steel pin into the end of the rung to kink and squash the wire for it to hold the rung firmly, and had been condemned in an article by Jim Eyre in Descent No. 7, though he did not give any experimental evidence to support his criticism. So we performed a series of tests in the Engineering Department Laboratories to find out precisely how much the method weakened the wire, and how firmly it held the rungs. These tests, summarised at the end of the article, refuted his claim that taper-pins weaken the wire and give a firm fixture, so we decided to use this method for our ladders.

Actually fixing the rungs in place took very little time indeed - two people, a hammer, and a wooden rung-spacer were able to make 20' of ladder in about. 15 minutes - but chamfering the ends of the taper-pins on grindstones to make them easier to drive in did take a long time. Nevertheless after two days and at the expense of a few bashed and several scorched fingers (doesn't grinding make a taper-pin hot!), we had a 150 ft. of made-up ladder. Random rungs were tested by the inelegant but adequate device of suspending the ladder by a single rung from an Engineering Lab. framework and having three people hanging on the ladder. Not one failure, so the ladder was taken over to Simpers Ropeworks Limited, who added the c-links to the ends and spliced them on with a talurit thimble.

The new ladder has now (October) been with us for three months, during which it has been used for the Ireland expedition, six-day President's Invitation Meet and one week-end meet. It is almost twice as heavy as the old ferrule-fixed ladder, but this has not proved a problem and is offset by its far superior 'feel' when climbing; no longer the irritating ½" of play on the rung when you reach up for it, and no more gloves left trapped between rung and ferrule half-way down a pitch.

Most members of the Club think it is a better ladder to cave with. One or two taper-pins have shown signs of easing out but this trouble will soon stop when the ends of the rungs have been plugged with Araldite. 50 feet of ladder remain to be finished, and when this is done and the new batch of belays completed, we shall have made 200' of ladder and 100' of belay for just over £35.


These were carried out in the Structures Laboratory of the Engineering Department. The ladder tested was made 5 years ago by Tolworth Venture Scouts Unit and had been withdrawn from service owing to taper-pins coming out, with subsequent damage to the wire.


Wire rope:5/32" diameter 19 cwt. construction 6/7/1 hemp-cored
Rungs:16 SWG, HT 30WP
Taper-Pins:¼" diameter, MS

Two different tests were done on sections of the ladder.

(a) Wire Strength

The wire was pulled across the rung to test the breaking strength of the wire.

Fig.1 2k png


Strands of wire began to break at:

(i) 1470 lb.f.
(ii) 1560 lb.f.

This represents a strength of 69% of the original strength of the unused wire (2138 lb.f.)

(b) Rung Slip

Wider pins were used to ensure the pull was only on the rungs.

Fig.2 3k png


(i) Rung slipped at 570 lb.f.
(ii) Rung slipped at 580 lb.f.
continued to slip steadily at 500 lb.f.

These tests proved the taper-pin method could provide a firm rung fixture without too much reduction in strength of the wire.

To find the optimum size of the taper-pin for the C.U.C.C. wire (10 cwt) two tests were made of rung slip:

Size of pinSlip (lb.f.)

5/16" taper pins were adopted.


[ Web Editor's note (1998): The hemp-cored rope used in these ladders proved to be a poor choice, as the hemp retains water and the wires rust from the inside, where the damage is effectively invisible. A number of accidents have occurred due to use of this type of wire, which is not used by anyone today. Nowadays, CUCC, like most other groups, uses the pin-and-araldite construction. ]

A Note on the C.R.O.
CU 1971 Contents Page Next:
Research Group Report