First make mould
No. 1 as described in Fig.
1.11.
Any close grained timber will do, provided it is free of knots. The
mould itself is mounted on a base of blockboard. The outside of this
mould must be made with great care, scraped, glasspapered, button
polished, glasspapered again, and French polished.
Then it is coated
with a polish containing a good proportion of carnauba wax, buffed
with a soft cloth, and waxed again six times. This wax coating serves
as a parting or release agent to which the resin will not adhere.
When the female wooden mould is made, you can make the male mould
from it as shown in Fig.
1.11.
Mould No. 1 may
now be discarded. It is advantageous to reinforce the outside of Mould
No. 2 with battens and strips of glass fibre and resin; a mould made
this way will last a long time. Apply several coats of release wax
on the inside as you did for the female mould.
To make the skin,
the resin must be pigmented "British racing green" colour,
or black. First apply the pigmented gel coat.
Let it become tacky
and lay on it some open-weave glass cloth, then apply more resin with
a stippling action of the brush until the cloth is saturated. Air
bubbles trapped under the cloth must be removed by further stippling
action of the brush, or by using a special roller.
Place another layer
of cloth over the first, and soak it again with resin; a third layer
of cloth should be applied in the same way. Each coat of resin sets
in about 30 minutes.
Trim the edges
with a sharp knife before the resin is cured, and unmould after about
three hours. Put the skin back into the mould in order to prevent
any distortion during the curing process.
Now fit the baseboard
against the bottom of the soundbox as previously described.
With a sharp pencil
scribe carefully around the inside; draw another line 5mm outside
the first, and cut the base along this second line, so that you have
enough wood left to accommodate the bevel.
Cut the round hole
in the base and bevel the edges to fit snugly inside the skin.
When the fitting
is good, coat the bevelled edges with plenty of resin.
Take the skin out
of the mould and secure the base to the skin with panel pins, starting
at the middle, one panel pin every 30 mm.
Prepare the top
piece and secure it in position with panel pins and resin.
Prepare the side
rails and fix them along the sides with more resin and panel pins.
When the resin is fully cured, the whole structure will be very strong
and there will be no need for frames to strengthen it.
Now, with a sharp
awl and a template made of stiff card, scribe the three elongated
soundholes at the back and cut them out with an electric jig saw or
a new key-hole saw.
Glasspaper the
edges, and brush a coat of resin over them in order to cover up loose
fibres.
Apply one more
coat of green resin over the inside.
Smooth the outside
with very fine "wet and dry" abrasive paper, then with a
rubbing compound, so that the skin is ready to receive one final coat
of cellulose paint from an aerosol can (B.M.C. Dark British racing
green). This final touch is done when the harp is finished because
there are still a lot of things to do which could spoil the lacquer.
The skin is now
ready to receive the soundboard, and this may be secured in the same
manner as already described for the two previous methods of construction.
