_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.
[Illustration: FIG. 63]
[Illustration: FIG. 64]
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).
[Illustration: 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.
[Illustration: FIG. 66]
[Illustration: FIG. 67]
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.
[Illustration: FIG. 68]
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.
[Illustration: FIG. 69]
[Illustration: FIG. 70]
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.
[Illustration: FIG. 71]
[Illustration: FIG. 72]
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.
[Illustration: FIG. 73]
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.
[Illustration: FIG. 74]
[Illustration: FIG. 75]
[Illustration: FIG. 76]
[Illustration: FIG. 77]
[Illustration: FIG. 78]
[Illustration: FIG. 79]
=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.
[Illustration: FIG. 80]
=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.
[Illustration: FIG. 81]
[Illustration: FIG. 82]
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.
[Illustration: FIG. 83]
[Illustration: FIG. 84]
[Illustration: FIG. 85]
=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.
[Illustration: FIG. 86]
[Illustration: FIG. 87]
[Illustration: FIG. 88]
[Illustration: FIG. 89]
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.
[Illustration: 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.
[Illustration: FIG. 91]
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.
[Illustration: FIG. 92]
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.
[Illustration: FIG. 93]
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.
[Illustration: FIG. 94]
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.
[Illustration: FIG. 95]
=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.
[Illustration: FIG. 96]
[Illustration: FIG. 97]
[Illustration: FIG. 98]
[Illustration: FIG. 99]
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.
[Illustration: FIG. 100]
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.
[Illustration: FIG. 101]
=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.
[Illustration: FIG. 102]
=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.
[Illustration: FIG. 103]
=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.
[Illustration: FIG. 104]
=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.