3.  B.E.C. STANDARD LIGHTWEIGHT LADDER- Materials & Preparation

The first ladders built to this pattern were constructed in 1949-50.  There were a number of faults in these early ladders but it is believed that these have been overcome.  The descriptions given are amplified by the drawings of the component parts.

End Plugs.  These are-made from 1/2" diameter Duralumin rod and are cut 1" long. They are drilled and tapped-along their length to take the 1/4" Whitworth grub-screws that are used. Duralumin is preferable to aluminium as it is considerably easier to drill and, in particular, to tap the holes.

One of the major defects of the earlier ladders was the design of the end plugs.  They were made as shown in figure 2(a) and due to the tapped hole stopping as shown the grub-screw, when tightened, forced the wire into the aluminium.  Under load this deformed and let the rung slip, down the wire.  One remedy that was tried was to insert a plug of aluminium between the grub-screw and the wire as it was thought that the tapping was not deep enough but this was not successful, the rung still slipping.  The ladder was eventually dismantled and the grub screw holes drilled and tapped right through, as the present design, then reassembled using new wire.  After the initial bedding-in, no more trouble was experienced.  With this method the wire is forced into the hole and given a kink when the screw is tightened.   This kink is not severe enough to weaken the wire appreciably but does positively prevent slipping of the rungs.  The present method is shown in figure 2(b).

Figure 2

Rungs.   These were originally constructed of 3/4"o.d. x 1/16" wall aluminium alloy tubing but a cheaper substitute was found by using 3/8"o.d. commercial aluminium electrical conduit.  This suffered from the drawback that the wall thickness is greater than 16 gauge and a press of some sort is needed to insert the end plugs.  All later ladders were constructed from 5/8"o.d. x 16 gauge wall alloy, tube and in this case, the end plugs are made from 1/8" rod. All other dimensions of rungs are as stated on figure 3.         To facilitate the construction of the large number of rungs required, a cutting and drilling jig has been constructed for 5/8"o.d. rungs.  This is shown, in figure 4 and is case hardened all over and is surface ground on both sides.  The rungs are cut to length by sliding in a length of tubing flush with one end and then cutting down close to the other end with a hacksaw, finally filing the end square against the jig.  The burr on the outside of the rung can either be removed by filing or by rotating the rung against a sanding disc of a 3/4" electric drill.  At the same time the rung end should be chamfered. The burr inside the rung is best cleaned by rotating a round nosed parallel rotary file exactly 1/2" diameter in a 1/4" electric drill fitted in a bench stand, then feeding the rung end on to the rotary file for not more than 1/8".  This provides a starting guide when pressing the plugs in.

Figure 3

The next operation is to insert the end plugs.  The plugs for the earlier ladders were a sliding fit in the tube and this was found to be a serious drawback as after the wire holes were drilled the plugs slid out of line.  For this reason the practice has since been adopted of using 16 gauge (0.064") wall thickness.  With 5/8” o.d. tube the inside diameter is 0.497" and this gives an interference fit of 0.003" when using 1/2" diameter plugs.  The plugs are pressed into position, one at a time, by using a carpenterÙs cramp as shown in figure 5.

Figure 4

Figure 5

After inserting the plugs the rung is placed in the cutting and drilling jig and the holes for the wire drilled using a 1/8" drill.  If the rungs are made of Dural or a similar hard alloy the holes are slightly countersunk to remove the sharp edges.  It has been found that some of the individual strands of wire in contact with the hole broke after a few months use if this was not done.

Grub Screws.  These are 1/4" Whitworth x 1/4" long hexagon socket grub screws, preferably of "Allan" or "Unbrake" manufacture.  The type of end of these screws varies, figure 6, but the only one readily available is the half or reversed cup point (a).  Although this is not ideal it seems to serve well in practice.  There is one variation of this that must not be used and this is where the cup point is serrated.  This, when tightened, cuts into the individual wires of the rope.  The preferred type is the cone point of 60° (b), if this can be obtained, as this causes no damage to the wire.

Figure 6

Wire Rope.  Originally this was 10cwt aircraft cable of 7/19 construction but now 15cwt cable of similar construction is used as the cost is the same.  This type of cable is extremely flexible and is made of seven strands, arranged as (a) in figure 7, each strand being made from nine teen wires (b), and each individual wire, approximately 0.01" diameter is galvanised.  On no account should a wire rope be used with a fibre core as this acts as a sponge holding water in the centre of the rope and thus accelerates corrosion. (Editor's Note: Fibre cored wire ropes have been used satisfactorily for caving ladders without corrosion - see Caving Report No. 3A.)

Figure 7

End Fittings (C-Links).  Considerable variations exist in the type of end fittings but the most popular is the C-Link and this has been standardised for all B.E.C. ladders and ancillary equipment.  The simplest is undoubtedly a link cut from a piece of chain.  Various chains were cut and tested on a tensile testing machine and the low figure at which most links failed was rather surprising.   Loads in the order of four or five hundredweight resulted in the links opening right out as shown in figure 8.  Tests were continued until a section of 3/8" close pitch chain was found to stand 520 pounds before any opening of the gap occurred. The loading was slowly increased with the gap gradually widening until at a load of just over nine hundredweight the link opened fully with no increase of load.  The link showed no sign of fracturing.  This chain, which was manufactured from E.N. 8 steel, was considered to be more than adequate for the purpose and a length was obtained - sufficient for several hundred links.  As the facilities were available these links were cadmium plated and this does in fact give a finished look to the completed ladders.

Figure 8

Thimbles.  The wire end is passed round a tinned iron or stainless steel thimble which contains the C-Link.  The readily available thimbles are designed for 1/2" circumference rope which is slightly larger than 10 or 15cwt. aircraft cable.  The correct thimble for the aircraft cable seems to the writer to be rather small and flimsy and so the 1/2" circumference thimble has been used, being flattened to the diameter of the rope used.

Wire End Fixing.  Two methods have been used for finishing off the ends of the wire.  The earlier ladders using 10cwt cable were clamped and soldered in a ferrule.  All the later ladders using 15cwt cable have been spliced.

Figure 9

With the ferrule method a one inch long piece of 1/4"o.d. copper pipe is carefully cleaned and flattened in a vice to the shape shown in figure 9, just sufficiently to slide two sections of the wire through it.  The ferrule is then thoroughly tinned inside and out.  This is important as otherwise corrosion could be rapidly set up between the copper and zinc coating of the wire.  The wire has then to be tinned either side of the thimble for an inch only, and the free end cut so that it stops just at the end of the ferrule.  To assemble, slide the ferrule on to the wire, then pass the wire round the thimble containing a C-Link and finally slip the end of the wire into the ferrule again. After pulling the wire tight round the thimble, the ferrule is squeezed as flat as possible in a vice and then the wire-ferrule assembly is soldered up.  When soldering care must be taken not to apply any more heat than necessary and under no account must a naked flame be used as otherwise the temper of the wire is lost.  For the same reason a tin-lead solder is also preferred.  It will be obvious that a non-corrosive flux is essential and for this purpose "Alkaray" flux, which is approved by the Aeronautical Inspection Department as being non-corrosive, has been used on all the later ladders.  It is also necessary to clean the wire well before soldering and methylated spirits, carbon tetrachloride or a similar solvent are required to remove the oil incorporated in the rope during manufacture.  The "Alkaray" flux has none of the penetration of, say, ''killed spirits" and in practice has been found difficult to solder rope which has been kept in stock for a period when the zinc coating has tarnished.  (Editor's note: This method of forming end loops is not to be recommended as the long term effects of the solder on the rope are not known, see the revised edition of Caving Report No. 3.)

Eye splicing the cable end seems to be the safest method as it is possible to inspect the splice periodically by removing the binding, whereas with the ferrule method it is possible for the wire to corrode in the ferrule and the first warning is when the ladder breaks in service.  The difficulty of splicing the cable is not great and anyone can splice a hemp rope can, after a little practice, make a fair splice in wire rope.  However, it is a tedious job and painful on the fingers. The writer, who is by no means an expert at the job, finds it takes approximately an hour to make one splice. The writer's technique is first to bind the cable five inches from the free end and then open out the strands back to the binding and solder the cut ends of each strand for 1/8" to prevent the individual wires coming apart.  Baker's Fluid or "Fluxite" can be used for this as the ends will be cut off later.  Then assemble the cable round the thimble containing the C-Link.  The cable should be bound to the thimble, or the method the writer finds easier, using the oversize thimbles, is to close over slightly the outside of the thimble so that-the wire is held securely.  Then remove the binding from the free end of the cable.  Various ways are possible for making the first round of tucks and the method adopted by the author is that given by the British Standard Institute for splicing wire ropes.   Details are given in the Appendix.

The British Standards Institute specify a five round splice three rounds of full strands and the last two with approximately half of the wires cut out, thus causing the finished splice to taper.  The writer, however, prefers to make four full rounds and then two with halved strands just to be on the safe side.  These additional rounds of tucks are made in exactly the same way as the second round, being pulled tight and beaten after each round.  Finally the surplus wire is cut off sand the whole splice served (or bound) with either waxed twine or small diameter (20 gauge maximum) galvanised wire.  The purpose of the binding is to hold the whole splice tight and to cover the short projecting cut ends of wire.  The waxed twine is preferable as it leaves the splice relatively flexible but it is liable to chafe or rot through under cave conditions unless frequently inspected and renewed.

One point that is worth taking some trouble over is getting the distance of the ends, from the rungs, correct.  This should be 5 1/2" from the centre of the end rung to the inside of the far end of the C-Link so that when the ladders are joined the rung spacing remains at an 11" pitch.  If care is not taken it will be found that one side will hang lower than the other, which makes it disconcerting when climbing the finished ladder.

Another method of finishing the ends is the "Talurit" splicing process. This is similar to the ferrule method except that the ferrule is a thick aluminium sleeve which is swaged on to the rope .by means of a hydraulic press.  This process is usually done commercially and tends to be expensive, costing 2/11d per splice although a reduction in price is made when more than six are done at one time.  In comparison, the charge for a hand splice, made commercially, is 1/9d irrespective of the number.

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