Well-made ropes in diametres below 0.5 mm are rather scarce or
unavailable at all commercially or only in a few sizes and
colours. So
serious miniature shipmodeller has to resort to make his
own.
There are various descriptions of ropewalks in the modelling
literature
and on the Internet to be found. One can also inspect full-size
preserved examples, for instance the one at the
Chatham
Historic
Dockyard.
Essentially, a ropewalk consists of a headstock with a planetary
drive
the gives the individual strands a twist against the 'lay' of
the rope,
while at the other end there is a tailstock drive that twist the
rope
together. A travelling bobbin (the denomination varies) ensures
that
the strands are separated and then fed together in a controlled
fashion. However, Bernard Frölich (1999) suggested that,
when one
keeps the strands apart at the tailstock end and then twists
them
together, the rope will start forming from the middle of the
walk,
progressing towards the headstock and tailstock. It is this
principle
that was used for the miniature ropewalk.
In my late fathers estate there was an optical bench with
several
'steadies'. The bed is triangular in cross-section and is, as
the
steadies, made from solid dark-brown bakelite. It dates probably
to the
1940s and was supplied by the well known German demonstration
instrument company
PHYWE.
Not
sure
what my father would say about this
new use, but after decades of slumbering in a dark corner of his
study,
it was calling for a new lease of life. It appeared to be a good
base
for a ropewalk and perhaps later also a serving machine, if I
ever
should need one.
Apart from the gears that were mostly bought for the purpose,
the
ropewalk was constructed from pieces found in my scrap-box. The
design
evolved while I was assembling it, so some aspects are not as
well
thought-out as I would wish. For instance, for the headstock I
should
have purchased six pinions and installed them permanently in a
hexagon.
I was too mean and bought only four.
The body of head- and tailstock is a small slab of 6 mm brass.
The
holes for the shafts were drilled and reamed to size. On the
side that
would have to take up the pull of the rope a 90° cone was
sunk to
create effectively half a cone bearing. This a better defined
position
than just a cylindrical bearing. The driving shaft in the
headstock was
left somewhat protruding to allow fixing at a later date a clamp
for
holding very thin wires for twisting them together. The hooks
were bent
from iron wire and hard-soldered into the shafts, as were the
hooks in
the driving plate of the tailstock. The driving shaft of the
tailstock
can be blocked by a thumbscrew that acts on a small brass pad,
but the
very thin ropes that I am making do not exert that much torque,
so this
may have been not necessary.
The steadies of an optical bench are not meant to travel, they
are just
set by a thumb-screw that screws into a triangular groove of the
bed.
However, the tailstock of a ropewalk has to move to allow for
the
shortening of the strands and the rope while being twisted
together. I
added round gibs made from aluminium rod. Round because I was to
lazy
to reproduce the odd triangular shape of the grooves. The
tailstock is
eased by hand to allow for the shortening because the rather
long stems
of the steadies lead to canting and thence to breaking of the
very
delicate ropes.
Depending on the direction of cranking, left- and right-handed
rope
with three or four strands can be made.
Reference
F
RÖLICH, B. (1999): L'Art du
modélisme.- 304
p., Nice (Editions Ancre).