- 1 Caving Report No 3
- 2 The Manufacture of Lightweight Caving Ladders
- 3.1 SECTION A – Materials.
- 3.2 SECTION B – Preparation.
- 3.4 SECTION C – Assembly.
- 3.6 SECTION D – Jigs used.
- 3.8 SECTION E – Approximate times involved.
- 3.10 SECTION F – Tensile strengths, weights and bulk.
- 3.12 SECTION G – Conclusions.
Caving Report No 3
The Manufacture of Lightweight Caving Ladders
by B.M. Ellis – May 1958
During March 1956, one hundred feet of lightweight caving ladder were made; first a ten foot length which was tested under severe conditions to ascertain the suitability of the method used, then one twenty and two thirty five foot lengths these lengths being regarded as the most suitable for use in Mendip caves. This report deals, in detail with the method used in the construction of these ladders.
Detailed specifications will be found in later sections of the report, but the main specification of the ladders is:
Overall width of rungs 6″
Distance between wires 5 ¼”
Distance between rungs 10″
Method of rung fixing Taper Joints
Method of ladder joining “C” rings
The author’s reasons for deciding on this method of ladder construction will be found at the end of the report. The method of rung fixing by the use of taper pins is not claimed to be original; the author copied the idea from the Westminster Speleological Group ladders that he had used for many years and found to be very satisfactory. On checking these W.S.G. ladders after several years of service no case of rung slip was found to have occurred, nor had any damage been caused to the wires by the method of rung fixing employed.
The report is divided into seven sections under the headings given below:-
- Materials required, their suppliers, specifications and cost.
- Preparation of materials carried out prior to assembly.
- Method of assembly of the prepared parts.
- Details of the jigs used.
- Approximate times involved in the different stages of manufacture.
- Tensile strengths, weights and bulk of the ladders
The March, 1956 prices of materials are quoted as a guide some of these prices fluctuate, especially that of aluminium alloy tubing. Names and addresses of suppliers are also given for reference. All these suppliers are recommended as being quick and helpful.
Let it be said, though probably unnecessarily, that the author is not an engineer but he did have the advice of one.
SECTION A – Materials.
TUBING for rungs
The tubing used was BL 6 quality Dural tubing obtainable from:-
Blackburns ( London) Ltd.,
The dimensions of the tubing were 3/8″ O/D x 16 s.w.g., sold in thirteen feet lengths @ 9d. per foot. It can either be sent, when packing and carriage are extra, or collected from the firm’s warehouse in Stephen Street, London.
Flexible round strand rope of best plough steel with galvanized finish and plain ends. The construction of the rope is 6/19, i.e. six strands of nineteen wires each, with a fibre main core. The 1/8″ diameter rope used has an actual breaking strain (manufacturer’s figures) of 0.61 tons. The cost was £1/8/6 per hundred feet (which weighs approx. 2 1/4 lbs.), carriage extra. It is obtainable from:-
Bridgwater Wire Rope Works Ltd.,
Cadmium plated thimbles to take 1/8″ diameter rope of the dimensions shown in figure 1 are obtainable at 3d each, plus postage, from:-
William Good and Sons Ltd.,
46, Fish Street Hill,
Dimensions C=7/8″ B=1/2″ D=1/8″
ROD for taper pins.
The pins were cut from 5/32″ diameter mild steel rod obtained through a friend @ 1d. per foot.
TUBING for sleeves.
Copper tubing of 1/4″ I/D found lying scrap was used.
CHAIN for “C” rings.
Chain links having the dimensions shown in figure 2 were used. It was found lying scrap.
The quantities of these materials required for the manufacture of one hundred feet of ladder are:-
Alloy Tubing 65 feet.
Wire Rope 220 feet.
Mild steel rod 25 feet.
Sleeves, thimbles and Chain Links 4 each per length of ladder
SECTION B – Preparation.
The jig used for the cutting and drilling of the alloy tubing is described on page 5 and shown in figure 4. The rungs are cut six inches long and drilled 5/16″ from either end using a number 29 drill. The cutting is done by holding the tubing in the angle of the jig in a bench vise and cutting off square against the jig; the drilling by holding the tubing in the same position in the jig in a flat bed vise and using a vertical bench drill. Finally the ends of each rung and the drilled holes are cleaned using a fine file. The dimensions of the rungs are shown in figure 4.
The best method for cutting the wire rope was found to be as follows. Bind the rope with Wire of about 22 s.w.g. either side of the point to be cut, leaving about 1/8″ between the two bindings, and then cut with a hacksaw. The lengths of wire required are as follows:-
For Ten feet ladders 11 feet.
For Twenty feet ladders 21 feet.
For Thirty five feet ladders 37 feet.
One end of each cut length is left bound and the other is prepared for threading. The method finally adopted to prepare the end for threading is first to tin it with solder for a length of three inches with the original binding in place, then place a second binding above the first and cut between the two. The second binding is then removed and the end carefully cleaned using a very fine file; no loose strands of wire must remain. To tin the end of the wire, it should be immersed in a tube of molten solder for several seconds, removed, and the excess solder melted off using a micro-bunsen burner. Care should be taken to remove all the grease present on the wire when sold before soldering.
These are purchased ready for use.
All attempts to purchase something suitable were of no avail and the pins have to be manufactured from mild steel rod. The rod is ground to a flat taper on an ordinary bench grinding wheel using the jig described on page 5 and shown in figure 7. After grinding, the taper is filed smooth and the pin out to an approximate length of one inch. (See note in Section G.) The taper pins are of 5/32″ diameter, having a flat taper at an angle of 15 – 20 degrees to the length of the pin. The overall length of the pin is not critical as long as there is at least 7/16″ at the full diameter beyond the end of the taper.
These are cut ¾” long from the copper tubing, cleaned with a file and slightly flattened by a light blow.
Two cuts are made at an angle of 43 degrees to the length of the link, at the centre of on one side of each link. The cuts are cleaned using a large square file.
SECTION C – Assembly.
The parts comprising each header are shown in figure 5. A thimble is forced open, a “C” ring threaded on, and the thimble closed; the wire is threaded through a sleeve, around the thimble and back into the sleeve until the bound end is almost at the bottom of the sleeve. The complete assembly is pulled tight, and in this position the sleeve is squashed fairly tight. Either end of the sleeve is then soldered, using a micro-bunsen burner and soft solder (60% lead, 40% tin.)
The rungs are threaded on two wires which have had headers assembled at one end of each. The first rung is placed in the slot of the rung spacing and fixing jig (described on page 3) having the rung stop, and the rung is spaced exactly five inches from the top inside curve of the “C” ring by using the header distance attachment described on page 5. This distance of exactly five inches ensures that, on joining two ladders together, there is no difference in distance between rungs at the join. The first rung is fixed in position by hammering a taper pin between the inside of the rung and the wire, care being taken not to damage the wire with the pin. (The effect of the pin is shown in figure 6.). Having fixed one side, the ladder is reversed in the jig so that the other end of the same rung is then against the rung stop, and the rung is then fixed to the other wire in a similar manner. The pins must be placed on the same side of the wire for each rung, with reversal of the side for succeeding rungs – this is done to prevent any curling and spiralling of the ladder due to the slight bend in the wire imparted by the taper pin. Having fixed the first rang, the ladder is moved up in the jig and the position of the second rung taken from the one already fixed. One rung is placed in each pair of slots, the wires pulled taut, and a pin driven in. For this operation it is advantageous to have two people working on the construction. Due to the rung stop fitted to the jig, it is necessary to reverse the ladder before hammering in the second pin, but this operation also cancels out any errors that may be present in the construction of the jig.
Having fixed the last rung of the ladder, it is left in the jig and the bottom header assembled in the same manner as the top one. The correct position in relation to the bottom rung is obtained by using the header distance attachment. When the header is assembled in the correct position, it is pulled tight, the point where the cable left the sleeve being marked. The header is then disassembled and the wire cut at the mark made. It is then reassembled without using the jigs, pulled tight and squashed as mentioned in (1) above, and soldered, thus completing the ladder.
SECTION D – Jigs used.
RUNG CUTTING AND DRILLING JIG.
(see Figure 4.) This jig consisted of a length of one inch angle iron cut square at each end and exactly six inches long. 5/16″ from each end was drilled a hole using a number 27 drill, the distance of the centre of the hole from the angle being such that it lay vertically over the centre of a piece of 3/8″ diameter tubing held in the angle.
TAPER PIN GRINDING JIG.
(Figure 7.) A piece of 2″x 4″ x 1¼” brass was cut so that one side was at an angle of 15 – 20 degrees to the others. A hole of 11/64″ diameter was drilled perpendicular to this face and 1 1/4″ from one end. The width of the brass was then reduced by ½” to 1½” by sawing to cause the drilled hole to appear along the cut face. This operation was considered necessary because the decreased resistance on striking the face would have caused the hole not to be straight if the hole had been drilled directly to the face. Along the opposite face was soldered a two inch strip of 16 s.w.g. brass. A hole was drilled vertically across the original hole and tapped to take a ¼” Whitworth bolt to which had been brazed a butterfly nut. The width of the jig was such that a piece of 5/32″ rod placed through the hole and clamped by the bolt would just be ground by the grinding wheel used, the plate running along the edge of the platform of the wheel and thus preventing the jig itself from touching the grinding wheel.
RUNG SPACING & FIXING JIG.
(Figure 8.) Two pieces of ¾” angle Dural, twelve inches long, were bolted parallel, 5¼” apart, on a sheet of 12″x 8″x ½” Tufnol. In each length of Dural were cut two slots, 7/l6″‘ wide and exactly ten inches apart; these slots were ½” deep and were to take the rungs. Opposite one of these slots was bolted a short length of 1″ angle iron parallel to, and 7/8″ away from the Dural, to act as a stop for the rung when hammering in taper pins.
HEADER DISTANCE ATTACHMENT.
This consisted of a piece of 1¼” angle iron approximately 5″ long and drilled to take an O.B.A. bolt. The position of this bolt was such that when the angle iron was placed at the top of the rung spacing jig the bolt was exactly five inches from the centre of a rung placed in the top slot of the jig.
SECTION E – Approximate times involved.
These times must be taken as being very approximate, as times per job decrease rapidly with the number done. These times are the average of those taken by the author. Further more, extra time must be added for experimentation with methods available, manufacture of jigs, and miscellaneous hold-ups such as replacement of broken hacksaw blades and treatment of burnt fingers obtained when grinding taper pins.
Cutting…………………………………………. 15 seconds each.
Drilling…………………………………………. 20 seconds each.
Filing……………………………………………. 60 seconds each.
Measuring, Binding and cutting…… 4 minutes per length.
Tinning ends for threading…………… 3 minutes per length.
No preparation necessary.
Grinding……………………………………….. 30 seconds each.
Filing and cutting………………………….. 30 seconds each.
Cutting………………………………………….. 15 seconds each.
Filing…………………………………………….. 30 seconds each.
Cutting………………………………………….. 90 seconds each.
Filing…………………………………………….. 60 seconds each.
Assembly……………………………………… 4 minutes each.
Soldering………………………………………. 1 minute each.
Threading……………………………………… 15 seconds per rung.
Fixing…………………………………………….. 90 seconds per rung.
Assembly……………………………………….. 8 minutes each.
Soldering………………………………………. 1 minute each.
These times apply to one person working except in the case of rung fixing (Two people) and drilling rungs (Two people, two vises and one drill). The times include putting into, and taking out of, appropriate jigs.
SECTION F – Tensile strengths, weights and bulk.
Before use underground, each ladder was subjected to a general test by hanging each end in turn from a tree, and making the ladder take the weight of two people, their weights totalling 340 lb.
Tensile strengths were applied to the following, “C” rings, end loops and rung fixing. In each case the load was applied as fast as was possible on the machine, approx. 1,000 lbs per minute. Although this rate in no way represents shock loading, it is felt that the figures obtained are still relevant as only in very exceptional circumstances would a caving ladder be subjected to shock loading.
“C” Rings. Eight chain links of the type used were cut through one side of the link and tested in pairs. In each case, the links started to open at the same load.
End Loops. Four loops were made in exactly the same manner as those used on the ladders, one loop on either side of a short length of cable. The weaker loop of each pair is thus the one whose strength is recorded. Both these loops slipped at the weight given below.
Rung Fixing. A short length of cable was centrally fixed on a rung by means of a taper pin as used in the construction of the ladders, and pulled. The rung was found to slip at the figure quoted below but serious failure of the materials did not occur. Two samples were tested in this manner, both slipping at the same load; in one, the hole drilled to take the wire was slightly enlarged on one side and there were two broken wires ( out of 114 ), in the other no damage was visible.
“C” rings started to open at 675 lb. (0.3 tons)
End loops slipped at 1,010 lb. (0.45tcns)
Rungs slipped at 560 lb. (0.25tons)
For interest and comparison purposes, tensile strengths were determined of an eye splice made in the cable and also of a loop in the cable secured by means of a shackle. With the former, the cable broke at the bottom of the splice at a load of 1,120 lb. (0.5 tons), while at this loading there was no sign of slip in the shackle. It was considered that the bulk and weight of a shackle was not justified by the increase in strength of 110 lb. over the soldered loops, especially as the soldered loop was not the weakest part of the ladder. Similarly for the extra work involved in making an eye-splice in the cable
WEIGHTS AND BULK
Weights and bulk of the finished ladders.
Diameter when rolled
SECTION G – Conclusions.
The time taken for the design, assembly and construction of the four ladders was longer than that expected at the outset as they took about thirty man hours to complete. This time includes the manufacture of all the jigs and experiments to find the best method of accomplishing various tasks. The time taken for the construction itself was about twenty man hours. Perhaps if more cavers helped with the construction of caving ladders they would then realize the work involved and therefore take more care of the tackle they use.
When making a further ladder at a later date only one item was changed from the method described in this report. This was to do away with the taper pin grinding jig and to make the taper by holding the rod in a vise and using a very coarse file. This method was found to be quicker, easier and also prevented the serious overheating of the metal.
The overall cost for the construction of one hundred feet of ladder was approximately £6 – 5 – 0. The cost may be divided very roughly as:-
Wire Rope £3 – 4 0
Rungs £2 – 9 0
Taper pins 2 0
Thimbles 4 0
Carriage on goods 6 0
Sufficient materials remained after the construction of the ladders to make a ten feet length of “knobbly Dog.” This consists of a single wire rope on which are mounted centrally three inch lengths of alloy tubing at one foot intervals. It is used as a hand line on near vertical slopes. The tubing for this was fixed in a similar manner, that is by use of taper pins. To ensure that the pins were driven in to the correct position, a small diameter punch, marked at the correct depth, was used.
For considerations of cost and bulk it was decided to make the ladders as narrow as practical. Having cut the rungs to give a width of 5¼ inches between wires, some doubt was felt in practice but no difficulty has been experienced, by people using size 10 boots. (The author does not know of anyone with bigger feet having used the ladders). The ladders have been extensively used since manufacture, and everyone who has climbed on them has pronounced them entirely satisfactory.
The choice of a rung distance of 10 inches was made with ease of climbing the longer pitches in mind. For pitches of over eighty feet, a rung distance of twelve inches had been found uncomfortable, especially by the shorter caver.
The choice of ladder length’s will always be a matter for discussion; just let it be said that this choice has been found satisfactory.
Originally, the ladders were carried by rolling as shown figure 56a of British Caving (Page 327) but this method was found to impart a kink in the cable at the start of the roll. More recently, the ladders have been carried by folding them backwards and forwards at every other rung, and tying. (see figure 56c in British Caving) This method has been found convenient and is definitely quicker than rolling.
In conclusion, the author would like to thank all the people who helped in the construction of these ladders, many with advice and some with practical help.
B.M.Ellis, January 1957.