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COACHBUILDING
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A potted history.
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Coach building as a craft which really
took off in Tudor times when horse drawn carriages became more sophisticated,
replacing the lumbering cart like vehicles of medieval times. The
growth of the industry continued into Stuart times with the rise of
the affluent merchant class. They could afford to have carriages built
which had previously been the preserve of the nobility and gentry.
Coach builders formed a craft guild, which received the Royal Warrant
In 1662 and became the Guild of Coach and Coach Harness Makers. Development
continued over the next two hundred years producing elegant vehicles.
With the advent of the motor vehicle in the 1880s coach builders soon
turned their attention to this novel form of transport and after a
brief transition period were soon producing bodies which looked more
like cars and less like horse drawn vehicles. The way was paved for
the superb styling examples of the 1920s & 30s. |
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Choice of timber.
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Seasoned ash is the choice of the coach
builder, as this timber has the most important advantages. As follows.
- Great resistance to torsional or twisting motion due to the
elasticity along the grain.
- Ease of working. Ash is reasonably easy to work which if chosen
carefully, having little awkward grain. It can be found in straight
grain sections ideal for cross bars and pillars etc. Areas of
curved grain can be found In many planks and these are used for
wheel arches rear cant rails etc. Regrettably ash is not very
resistant to rot or woodworm which necessitates repairs and rebuilds
so common nowadays.
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Selection of timber
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Slabsawn
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 Timber
for coach building Is primarily selected from the sapwood area of
the trunk. The trunk having been cut into planks at the sawmill it
will be seen that some planks contain only sapwood while others contain
both sap and heartwood. Heartwood, which forms the core of the tree,
is much harder than the sapwood. It absorbs all the stresses that
the tree is subject to as it grows and therefore contains many flaws,
such as knots, shakes, splits and awkward cross grains. Heartwood
does have its uses such as corner reinforcing blocks and body mounting
blocks.
Ash Is normally seasoned for three to five years, but these days It
is more likely to be kiln dried. A process which has to be very carefully
controlled so as not to take to much moisture out of the timber. Moisture
quantity In seasoned or kiln dried ash should be 10 to 15%.
Having selected his ash from the mill the coach builder stores his
planks In stacks of the same thickness with battens between each plank
to enable the air to circulate. Timber must be stored in an atmosphere
of stable humidity. |
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Design of bodywork and setting out.
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Having chosen a freehand drawn
design for a car body this is translated into a 1/5th or 1/10th scale
drawing showing side elevation, a half plan, rear elevation and front
elevation. These are then turned into full size drawings. One wall
of the workshop is rendered smooth and white washed, the full-scale
drawings set out thereon. The sizes and sections of the timbers are
set out and also the types of joints to be used. Next patterns and
dimensions are taken from the full-scale drawing and the timber selected.
The timber is then surface planned on one side, after which it is
thickened as required. Straight timbers are ripped down on the circular
saw and curved timbers band sawn. |
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Construction of a simple four-door saloon.
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Having prepared the timber and
cut out the necessary components the body is constructed thus. The
bottom sides are cut out and laid out on the chassis: housings are
marked and cut out for the cross bars. The cross bars are cut and
lapped into the housings in the bottom sides. Where the chassis rises
over the back axle the necessary chassis hump pieces are cut and housed
into the bottom sides. The back rail is then half lapped Into the
rear chassis hump pieces. Where the chassis manufacturers provide
an aluminium bulkhead a frame is then built following the shape of
the bulkhead and is housed Into the bottom sides. Next the position
of the windscreen pillars and hinge pillars are extracted from the
drawing and joints cut in the bottom sides to accept them. The pillars
are cut and dressed on three sides leaving the outside rough cut.
The pillars are then fitted to the bottom sides, temporary cross battens
are screwed to the pillars to keep them the correct distance apart.
The dash rail is fitted to the screen pillars. The wheel arches are
made next and these are formed from two or three sections halved together
to avoid excessive short grain. The cant rails are next fitted to
tenons cut into the tops of the pillars. Mortises having been previously
cut into them. With extra long cant rails it is sometimes necessary
to scarf two pieces together to form the cant rail. The rear cant
rail is next fitted this being stop scarfed to the cant rails. This
is followed by the screen top rail and rear window frame. Construction
of the roof frame is next. The inner cant rails are cut out and dressed
accept for the top face. halvings are cut to accept the roof cross
beams which are next fitted. Finally corner blocks are fitted between
the inner and main cant rails and shaped to the curvature of the roof.
1/8” packing pieces are next nailed to the shut faces of the door
apertures. The door shut pillars and hinge pillars are cut out and
fitted in, the top and bottom rails are halved in. Next the waist
rails are fitted to the doors with half housings. The rear waist rails
are fitted to the body so that they all line up horizontally as many
bodies carry a waist moulding all the way round. The doors are removed
and the glass runs cut, the garnish boards, winders, stop boards and
slats are fitted. Throughout construction NO glue is used on any joint,
security being provided by the tightness of the joints and the fitting
of steel screws which are greased before being driven home, If glue
is applied to the joints this results in the frame as a whole becoming
too rigid and torsional stresses are then transferred to the timbers
themselves cracking them unduly. It is permitted to apply white lead
or gold size to the joints to take up any slack in a badly cut joint.
Brass or bronze screws are not used as they are simply not strong
enough to be driven home In ash with a swingbrace or ratchet, the
screws would simply shear as they would if unduly stressed with vehicle
movement. |
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Panel work.
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A skilled panel beater makes his work look easy, this is an illusion.
It takes years to master the skills necessary to make new panels
or repair old ones to fit a body frame correctly. Stretching, shrinking,
beating, wheeling, bending, swaging and joggling all mostly by eye, then
welding and or brazing in alloy or steel are just a few of the operations
necessary to form or repair panels. An intimate knowledge of original
construction is essential in order to reproduce or repair in the
correct way. However well the body frame is constructed and shaped,
if the panel work is not correct the body will never look right.
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Joints commonly used in Coach work
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Copyright © Macros Solutions 2002. All rights reserved.
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