Chapter VI: Scaffolding Accessories and Their Use

=Ladders.=—A ladder consists of a pair of sides connected by a series of oak or ash treads or rungs. The sides of long ladders are formed by cutting lengthwise a straight fir pole into two pieces. Short ladders are made with square sides, but they are heavier and, as the grain seldom runs continuously throughout their length, also weaker.

The pole for the sides is selected for its straightness of fibre, for a twisted pole cannot be sawn lengthwise without cutting across part of the grain, which as before stated is a source of weakness.

The pole has to be bored for the rungs, and this may be done either before or after it has been cut lengthwise. It is better to bore first, as then the holes occur at coincident intervals on each side; the rungs by this means are kept parallel and level.

The rungs are placed 9 inches apart, and are from 1 in. to 1-1/2-in. in depth in the centre, decreasing to 5/8-inch diameter at the ends. The ends of the rungs are painted with red lead before insertion, and any projections are afterwards cut off flush with the sides. They can be fastened at each end with wedges (see fig. 63), or pins of 1/4-inch diameter can be cut through the sides, as fig. 64, to fix every fifth or sixth rung.

The first method is the better, as cross boring of the sides greatly weakens them; but as the wedges may work out, an iron rod 5/16-inch in diameter should be placed below every eighth or ninth rung, and bolted on the outside for extra security.

The iron rods should not be used as treads instead of the wooden rungs as they offer an insecure foothold. The rungs are considered to be dangerous for use when they have been reduced by wear to one half of their original depth. The best rungs are made from old wheel-spokes, as they are well seasoned. The sides, which may be of sufficient length to receive 100 rungs, are 9 inches apart at the top and from 12 to 13 inches apart at the bottom, according to the length of the ladder.

Extension ladders are useful where, owing to the varying heights of the work, different lengths of ladders are required. The two halves of the ladder are connected in various ways, but if well made they are easily raised and lowered. They should be used only for the very lightest work, such as painting, cleaning down, &c.

=Trestles.=—Trestles are used chiefly by painters plasterers, and mechanics engaged on work that is not at a great height from the ground or floor level, and for which a platform is required. They stand from 6 to 12 feet in height, and the rungs should be sufficiently wide to carry three boards for the working platform. They are made of yellow deal, with mortised joints and wrought-iron hinges (fig. 65).

=Steps.=—Steps are built up with two sides of the required height, about 5 inches wide and 1 inch thick; the top and bottom are sawn to a bevel so that they stand inclined.

The steps, which are grooved into the sides and fixed with screws, are about 6 inches wide by 1-1/2 inches thick, and increase slightly in length as they descend. This increase adds to the stability of the steps as the width of the base is increased. The distance between each step is from 7 to 9 inches.

At the back of the top step two legs about 2-1/2 inches wide by 1 inch thick are secured by strong flap hinges. The legs are framed together by two cross pieces, 3 or 4 inches wide and 1 inch thick.

The back legs, by opening out on the flap hinges, enable the entire framework to stand upon an even surface. To prevent the legs opening too far, they are connected to the sides of the steps by cords.

=Cripples.=—The simplest form of cripple is shown on fig. 66, which sufficiently explains the design.

This cripple forms a fixed angle with the ladder, which, in order to keep the platform level, can be laid only at one slope against the wall. The defect is removed if the cripple is hinged and fitted with a quadrant and pin, as shown on fig. 67. The platform in this case can be kept level by adjustment irrespective of slope of ladder. The bracket should be long enough to carry a platform three boards wide, but as a rule it carries two.

Cripples may project from either side of the ladder, and are usually hung on the rungs. An advantage is gained if, in addition to this, clips are provided to clutch the sides of the ladder.

=Buckets and Skips.=—Besides the ordinary pail, which needs no description, larger buckets are commonly used for carrying concrete, mortar, earth, or any other moist or friable material.

Fig. 68 shows the tipping bucket, or skip, which balances on its hinges at A. The hinges are so placed that they are above the centre of gravity of the bucket when empty, and below the centre of gravity when full. This position allows the bucket to remain upright when empty, but it will make half a revolution and empty its contents when full. To prevent this action occurring before it is required, a catch on hinges is fixed on the rim of the bucket at B.

While the catch is in the position shown, the bucket cannot tilt, but if it is turned back the bucket makes the half revolution required, and after emptying its contents, swings upright of its own accord.

Buckets are constructed of steel, and the standard sizes vary in capacity from 1/4 to 1 cubic yard.

For a similar purpose a steel box is used. In this case the bottom of the box is hinged, and on the catch being released, drops out, allowing the material to fall over any desired spot. The catch can be released from above or below by means of a chain connected thereto, and the bottom of the box regains its position when lowered to the ground for refilling.

Each box is fitted with a bow for chain hook, or lugs for chain slings; has a capacity of about 3 cubic feet, is made of steel plates, and may be round or square on plan.

=Baskets.=—Baskets (as shown in figs. 69-73) have a capacity of about 1 cubic foot.

There are three qualities of cane used in their construction: 'Mackerel back,’ recognised by its peculiar markings, 'Short Nature,’ and 'Squeaky.’ Of these, the first is the best, the others following in the order named. It is a defect of the baskets as ordinarily constructed that their handles and bottoms give way after very little wear. Several improvements have been put on the market, the best of which are shown as follows.

In fig. 69 the black line represents an iron hook bent to the shape required, and the cane plaited round as for the ordinary basket.

It is claimed that the handles and bottoms of these baskets cannot give way, and it is a claim that is probably correct.

Owing to the difficulties of construction due to the rigidity of the iron hoop, they cost more than the ordinary basket, and this, with their extra weight, is unfortunately against their general adoption. Variations of the same idea are shown on figs. 70 and 71.

In the first case (fig. 70) the iron is in two parts, which theoretically would allow of weakness, but in practice the basket answers its purpose well.

In fig. 71 the rigid ironwork is placed by a wire rope spliced to make a complete circle. This kind of basket is easier to make and less in weight than those just mentioned, but the cost of the rope keeps the price high.

Fig. 72 shows another safety arrangement. A is a tarred hemp rope built into the basket as shown, and the ends fitted with eyelets for hoisting purposes, the handles being kept for use by the workmen.

The arrangement is a practical one, and gives the required element of safety to the baskets so long as the rope remains sound.

Ordinarily constructed baskets can be made temporarily safe by passing the slinging rope or chain through the handles and round the bottom of the basket, as shown on fig. 73. To prevent the rope slipping, and to give the basket a flat bottom, pieces of wood can be fitted as shown.

=Navvy Barrows.=—Navvy barrows (fig. 74) are of hard wood, wrought and cast iron fittings and steel axles. They are fitted with iron, or wooden wheels bound with iron, and vary in weight from 60 to 75 lbs., and have a capacity of about 1/10 of a cubic yard.

A barrow of this class can be slung by passing a hook through the wheel and rings round the handles.

=Stone Bogies.=—Stone bogies (fig. 75) can be fitted with plain wheels for running on flat surfaces, or flanged wheels for rails. They are of oak, with steel axles and cast-iron wheels. The handles for pulling are detachable and adjustable to either end.

=Hand Barrows.=—Hand barrows as fig. 76 are useful for carrying light loads, and, when bearing material that cannot roll, may also be slung.

=Hods.=—Hods (fig. 77) are used on small jobs in which to carry mortar, bricks, &c. In capacity they will hold 2/3 of a cubic foot of mortar or twenty bricks, but an ordinary load is 16 walling or 12 facing bricks, the weight of which is considered to be enough for a man to carry up a ladder.

=Timber Trucks.=—Timber trucks (fig. 78) are used for carrying timber balks, iron girders, &c. They are usually 3 or 4 feet in length, with a width of about 24 inches and a height of 22 inches. They are made sufficiently strong to carry 6,000 lbs.

=Sack Trucks.=—Sack trucks (fig. 79) are constructed of hard wood, with fittings of wrought and cast iron and steel axles. They vary in length up to 4 feet 4 inches, and the foot iron projects from 6 to 9 inches.

=Crates=, as shown on fig. 80, are constructed of oak with iron bindings. They will carry a weight of 1,500 lbs. and hold 350 bricks. They can be filled in the builder’s yard and transferred direct to the working platform without disturbing the material, which, for saving time, is often of great advantage. The absence of sides facilitates loading, but on the other hand, if any materials, say bricks, are put in loosely, they may fall out during transference, causing danger to the workmen.

When used to carry rubble work which cannot be stacked, it is better that sides should be fitted.

When used to carry a roll of lead, a stay should be placed, as shown by dotted line on figure. This will prevent the crate buckling at the bottom.

These crates are sometimes fitted with wheels to run on rails.

=Ashlar Shears.=—The shears (figs. 81 and 82) are useful for lifting dressed work, the points fitting into small holes which have been cut out for their reception in the ends or sides of the stone. There is danger in their use if the points drag upwards and outwards. To prevent this as far as possible, the holes should be cut low, but not below the centre of gravity of the stone, or else it would turn over and perhaps fall.

Fig. 82 is a bad form of shears, as, owing to the sharp curve, the points can only clutch near the top of the stone.

=Stone Clips and Slings.=—The clips (fig. 83) are useful for lifting stone slabs. The hook rings slide along the chain, and the clips are therefore adjustable to any stone not exceeding in width half the total length of the chain.

The chain slings have a ring at one end and a hook at the other, and are useful for a similar purpose; but the manner of slinging depends upon the thickness of the stone. For instance fig. 84, known as jack slinging, answers well with a slab, say, of over 6 inches in depth, but a thinner slab lifted in this way would be liable to break in the middle. If, however, the chain were placed as fig. 85, and which is known as figure-eight slinging, this risk would be removed.

=Stone Lewises.=—Lewises may be divided into two classes, curved and straight-sided.

Fig. 86 shows the first, and fig. 87 the second class.

The first class is the inferior, as, when fitted into the stone, any jerk of the supporting chain would act at the points A as a blow on the stone, thus increasing any tendency to fracture.

The hole for the reception of the lewis is cut, so that a line down its centre would run across the centre of gravity of the stone; and it is made as deep as may be required by the weight and hardness of the material.

The side or splayed pieces of the lewis shown on fig. 87 are fitted first, and the centre piece last. A bolt through the top fixes their position and also the ring by which it is to be lifted.

Care should be taken that the sides of the second class of lewis fit accurately, for if they fit as fig. 88 they may flush the edge and break out, or if they fit as fig. 89 the risk of fracture, as in the first class, presents itself. In any case there is always a danger of mishaps occurring, especially where the stone is not free from vents.

Their use with safety can only be left to the judgment of the mason.

=Stone Cramps.=—The cramps tighten on the stone by means of a screw thread, as shown on fig. 90.

They are useful for lifting light finished work. Packing should be placed at AA to prevent damage.

The ring by which it is slung is movable to preserve equilibrium.

=Wire and Chain Scaffold Lashings.=—Wire rope scaffold lashings are now to be obtained for use in place of fibre cords. They are made in lengths from 12 to 18 feet, and are fitted at one end with an eyelet. In fixing, they commence with a clove hitch, the knot being continued as with a fibre cord until near the end, when the lash is taken through the eyelet (see fig. 91) and finished with jamming turns.

It is claimed that no wedges are required for tightening wire rope lashings, as they do not shrink or swell; on the other hand, owing to their small circumference, they cannot be pulled very tight by the workmen, and it is questionable if they would bear being twisted round the scaffolder’s hammer without injury.

Accidents also might happen if the poles shrank at all after being fixed.

Tests have been made from which it has been estimated that each lashing will carry a direct load of 6 tons.

A chain and bracket arrangement for tying ledgers to standards is shown on fig. 92. It is easily and rapidly adjusted, and is tightened by means of screw nuts at A and B.

Permanent injury might, however, be done to the standards by the cutting in of the brackets when screwed up, especially after regular use. The possible loss of the parts and their weight and consequent disadvantage in transport are against their general adoption.

=Tightening Screws.=—Tightening screws or coupling links (fig. 93) are fixed in the length of chain that connects the guys of the Scotch cranes to the base of the queen legs.

Under the continuous vibration of the scaffold they run down and release the chain considerably.

This can be prevented to some extent by inserting a piece of wood as shown on fig. 93, and tying its other end to a rigid member of the leg. In any case the chain requires frequent examination, and, if necessary, retightening.

=Rollers.=—Rollers (fig. 94) are used for moving heavy material along a smooth surface.

Pegs should be fixed at their ends, as shown on fig. 94, to form a handle by which they can be moved when under the material without danger to the workman’s hands, or better still, they should always be longer than the load is wide.

=Levers.=—Levers of ash, fitted with iron shoes, as fig. 95, are used to prise heavy material off the ground, to facilitate removal on rollers or otherwise. In this case the lever acts as one of the first order. By connecting the weight to the rings A and B it can be used as a lever of the second or the third order.

=Dog Irons.=—Dog irons (fig. 96) are bars of flat or round wrought iron, turned up at the ends, which are pointed. If both ends point in the same plane they are termed 'male,’ if otherwise 'female.’ The shank is about 12 inches long. Besides holding the timbers together, they exert a certain power of compression upon the joint they enclose. This is gained by hammering the inside of the spikes to a splay, leaving the outside to form a right angle with the shank.

They may be described as inferior straps, and their holding power is from 600 to 900 lbs. per inch in length of spikes, as deduced from experiments by Captain Fraser, R.E. Dog irons have the advantage that their use does not injure the timber to any extent, and so depreciate its value. Dogs are fixed according to the joint to be enclosed. If the joint is at right angles to the run of the timbers, they are fixed as fig. 97.

If the timbers are at right angles they are fixed as fig. 98.

If both these joints occur the irons are placed as fig. 99.

They should be fixed on both sides of the timbers joined.

=Bolts.=—Bolts (fig. 100) are of wrought iron, and their different parts should be in the following proportions:

Thickness of nut = 1 diameter of bolt
Thickness of head = 3/4 diameter of bolt
Diameter of head or nut over sides = 1-3/4 diameter of bolt
Size of square washer for fir = 3-1/2 diameter of bolt
Size of square washer for oak = 2-1/2 diameter of bolt
Thickness of washer = 1/3 diameter of bolt

There are disadvantages to the use of bolts in scaffolding. For instance, the beams are weakened by the cutting of the fibres; and, if the timber shrinks, the bolts may become loose. On the other hand, they can be easily tightened after the framing has settled into position.

Their strength depends upon the quality of the iron, but varies between 20 and 25 tons of tensile strain per square inch of the smallest sectional area (Anderson).

Washers are used to prevent the nut sinking into the wood when tightened, and are equally necessary, but not always seen, under the head. They should not be cut into the under side of timbers subjected to a cross strain, as the cutting of any fibres is a source of weakness. Bolts are used where dogs and spikes are of insufficient length or holding power.

=Straps.=—Straps are wrought-iron bands of different designs, and are used to form a connection between timbers. Branched straps (fig. 101) are used to strengthen angle joints. They are usually fixed in pairs, and being fastened on the surface of the timbers they have an advantage over bolts in that they do not cut into the material. If the timbers settle at all, the straps may become subject to cross strains.

=Wire Ropes.=—Wire ropes are now in general use for heavy purposes.

They are stranded and laid similarly to fibre ropes. They should be of mild plough steel wire. The number of wires in a strand varies from 12 to 37, and the number of strands is usually 6.

The following table gives the breaking strains of the ropes according to their circumference, and the least diameter of barrel and sheaves around which they may be worked at slow speeds.

In the table (p. 110) the diameters of the pulleys, &c. may be slightly reduced for the more flexible ropes, but better results can always be gained by using pulleys and sheaves of larger diameters.

A few points on the working of these ropes may be useful.

To remove a kink throw a turn out; it cannot be taken out by strain.

The ropes should be ungalvanised, and kept greased with any oil that does not contain acid or alkali.

A rope running in a V groove has a short life.

A rope that is allowed to ride, chafe on its own part or to overlap, will be almost immediately crippled.

The sign of an overloaded rope is excessive stretching.

+-------+-----------------------------+--------------+---------------+
| | | Extra | Special Extra |
| | Flexible Rope. |Flexible Rope.| Flexible Rope.|
| | 6 strands, each 12 wires | 6 strands, |6 strands, each|
| | |each 24 wires | 37 wires |
+-------+---------------+-------------+--------------+---------------+
| |Diam. of barrel| | | |
| Size |or sheave round| Guaranteed | Guaranteed | Guaranteed |
|Circum.|which it may be| Breaking | Breaking | Breaking |
| | worked at a | Strain | Strain | Strain |
| | slow speed | | | |
+-------+---------------+-------------+--------------+---------------+
|Inches | Inches | Tons | Tons | Tons |
| 1-1/2 | 9 | 4 | 7-1/2 | 8 |
| 1-3/4 | 10-1/2 | 5-1/2 | 9-3/4 | 11 |
| 2 | 12 | 7 | 13 | 14-1/2 |
| 2-1/4 | 13-1/2 | 9 | 16-1/4 | 17-1/2 |
| 2-1/2 | 15 | 12 | 20-1/2 | 22 |
| 2-3/4 | 16-1/2 | 15 | 24 | 26-1/2 |
| 3 | 18 | 18 | 28-1/2 | 32-1/4 |
| 3-1/4 | 19-1/2 | 22 | 34 | 37-1/2 |
| 3-1/2 | 21 | 26 | 39 | 43 |
| 3-3/4 | 22-1/2 | 29 | 45-1/2 | 50 |
| 4 | 24 | 33 | 51-1/2 | 56-1/2 |
| 4-1/4 | 25-1/2 | 36 | 59 | 65 |
| 4-1/2 | 27 | 39 | 65 | 70-1/2 |
| 4-3/4 | | | 74 | 79 |
| 5 | | | 82-1/2 | 88 |
+-------+---------------+-------------+--------------+---------------+

(_Bullivant & Co. Ltd._)

=Chains.=—The strength of a chain depends upon the diameter and quality of the iron of which the links are formed, governed by good workmanship. The safe load for working can be calculated approximately by the following method:—

Square the number of eighths of an inch which are contained in the diameter of the iron of which the link is made, and strike off the last figure as a decimal.

For example, where the iron is of 1/2-inch diameter, square the number of 1/8 in the diameter, i.e. 4 × 4 = 16 = 1·6 tons.

Generally before leaving the factory, chains are tested up to half the weight they should break under, and which is about double the load they are intended to carry in practice. This test cannot be relied upon for the future working of the chain, as any stretching of a link, which would ultimately result in fracture, would probably not be apparent under it. The links should therefore be examined periodically for any appearance of weakness or stretching.

A stretched link should at once be cut out, as it may break with much less load than that which it was first tested to carry. A chain during use also deteriorates in quality, and it is a good rule to have it periodically annealed.

The links should then be re-tested up to double the weight they are again required to carry.

A reliable chain is made of the treble best Staffordshire scrap iron.

Crane and pulley chains should be made with the shortest link possible, according to the diameter of the iron used, as there is a considerable leverage exerted on a long link when running round a pulley, more especially where the diameter of the pulley is small.

=A Slater’s Truss.=—Slaters’ trusses (fig. 102) are used in pairs by slaters and tilers when laying their material. Boards are laid across the trusses and form an effective platform on which the workman can kneel without damage to that part of the roof already covered. They are slung from the ridge or other suitable fixture, and can be pulled higher as the work proceeds. An old sack or similar material laid under the truss will prevent any possible damage during the progress of the work.

=Duck Runs.=—Duck runs (fig. 103) are laid upon slate and tile roofs to give footing to, and to prevent damage being done by, the workmen.

They should be firmly fixed, either by slinging from the ridge or butting against a solid resistance.

=Mortar Boards.=—A mortar board is used as a bed on which mortar can be mixed or deposited. It is roughly made of four or five 9-inch boards each 3 or 4 feet long, framed together on the under side. Their use prevents the new mortar coming in contact with the scaffold boards with an injurious effect.

=Wedges.=—A wedge is a movable, double-inclined plane, used for separating bodies, and by this means, tightening any connections between the bodies they tend to separate. For scaffolding purposes they should be of oak, or other wood which gives considerable resistance to pressure across the grain. For tightening cordage wedges should be about 12 inches in length and, as far as possible, split to shape. In cross section they should be semicircular. Their taper should be gradual and not too sudden, as otherwise they might work out. When used in pairs as for shoring purposes, they are rectangular in cross section, and are termed folding wedges.

=Nails.=—Cut nails stamped out of plates are best for scaffolds. These nails have the advantage of being easily drawn out of timber. When driven with their flat sides the way of the grain, they do not tend to split the wood. They are used to fix platform boards, and sometimes guard boards, on edge.

=Spikes.=—Spikes are nails above 4 inches in length. They form a cheap method of fixing. Captain Fraser, R.E., has computed from experiments that their holding power in fir is from 460 to 700 pounds per inch of length the depth of cover plate being deducted.

=Scaffolder’s hatchet.=—The scaffolder’s hatchet (fig. 104) is an ordinary shingling hatchet with a hammer head. It is practically the only tool used by the scaffolder. With it he can shape the ends of the putlogs, drive wedges, nails, &c., and, by giving the cord a turn round the middle of the handle, tighten knots by using it as a lever.