last updated 25/02/09
Wespe-Class Armoured Gunboat: The Model 
• Below you will find
a step-by-step description of building the model as it progresses •
However, this is not a continuous 'blog', so watch out for the date on
the beginning of paragraphs to identify new material
Scale
The scale
chosen for the model is 1/160, which admittedly is somewhat unusual for
a ship model. However, the reasoning behind this choice was that a
large selection of N-scale railway figures is available that eventually
will crew the ship. There are also space and portability consideration,
which are important for someone, who has to move from time to time for
professional reasons.
The model will be a waterline model.
This will allow a dioramic presentation of the finished model. Besides,
the hull below the waterline is not quite so graceful. Above the
waterline the hull is also more or less prismatic, with vertical
bulwarks and virtually no sheer. These parameters together call for a
bread-and-butter construction.
The building drawings are a
combination of
re-drawn Admiralty plans and scans thereof. These are printed to scale
on the laser printer and the print-outs glued on top of e.g. the MDF
board to
serve
as a guidance for cutting and sanding.
Materials
I had
been contemplating a variety of materials for the hull; for instance
Plexiglas® layers with bulwarks made
from brass foil. In the end, I choose MDF (medium-density fibre)
board, which is available in thicknesses down to 1 mm from
architectural model supply houses. Other
parts will be constructed from or covered with Bristol board, which is
also available in various
thicknesses (or rather weights per square metre). The bulwarks etc..
will be made from Pertinax® (phenolic
resin impregnated paper, FR-2),
which is available in thickness's down to 0.1 mm. Bristol
board and then Pertinax® are
easily cut with a scalpel, a razor blade or scissors and will not
crease or dent
as metal foil might. I currently
have no facilities for photo-etching large parts, but if I
had, perhaps I would have made the bulwarks from brass still. The other
advantage is that Bristol board can be readily and permanently glued
using white glue. Bonds between large areas of metal foil and Plexiglas® might become detached, though the plating on
the steam-tug,
made from copper foil, has lasted now for nearly twenty
years. Pertinax® can be
glued using cyano-acrylate or epoxy-resins. The dinghy of the steam-tug
had received planking made from Pertinax® and glued with cyano-acrylate glue.
While I have been shying away from thermoplastics, such as polystyrene,
on account of it being suspicious to be not 'permanent' (e.g. the articles
by Dana Wegner), practical experience shows that plastic models
built over 35 years are still intact. So I may reconsider my position
in this respect. Polystyrene, of course, has several advantageous
properties.
The hull
and superstructures
Autumn 2006 - The basic
bread-and-butter construction of
the hull is shown in the pictures above.
The Barbette mainly consists of a semi-circular breastwork armour,
backed by hardwood and by an open space covered with thin plate. The
latter presumably to retain splintering wood in case of an impact.
Since no tube of suitable dimensions for the breastwork was to hand, I
made a short
laminated one from Bristol board glued together with white glue. The
edges were soaked in thinned white glue before being trimmed down on
the lathe. The tube then was varnished with filler for wood before
the edges were sanded. Finally a half-circle was cut from the tube on
the jig-saw. More wood-filler was applied before final sanding. After
cutting in half it was glued into place. The inside of the barbette was
lined with hard-paper to give a smooth finish.
The fore-deck has been covered in a sheet of thin Bristol board and the
camber of the wooden decking built up with an additional piece of board
and putty (I am using fast drying bodywork putty from car repair
suppliers). The anchor pockets have also been lined with thin Bristol
board, but Pertinax would have been better for this.
All surfaces that would have been iron plating, will be covered in thin
sheets of Pertinax. The necessary holes for portholes and other opening
will be drilled or cut before the sheets are fixed.
The 30.5 cm Rk/l22
gun
Lower
Carriage
February
2007 -There are some fixtures for the gun that need to go
into their place in
the barbette early during the construction, including the races for the
gun carriage and the semi-circular toothed rack that is part of the
gun-training machinery. I decided to make these from steel, even though
ferrous metals in model construction are frowned upon by museums. My
justifications were that it is difficult to represent cast iron or
steel by paint and that there hundreds of models in museums around the
world that contain iron. I have used steel it in models some twenty
years ago and presumably due to the lacquering shows no signs of rust.
Cutting thin disks from round stock of sizeable diameter is a pain I
wanted to avoid. Against my better knowledge I picked a suitably sized
steel washer as starting material. Unfortunately, the steel used does
not cut very well at all and lot effort was spent to avoid chatter
marks while turning and to obtain a reasonably good finish. The various types of wheel collets available for
the watchmaking lathe come into good use for working on inside and
outside diameters of the disks.
I set up the hand-shaper for cutting
the rack teeth, but had to throw away the first two attempts because of
the poor material and because - again against better knowledge - I did
not lock the traverse slide when cutting. The table was removed from
the shaper and the home-made dividing head bolted on instead. For lack
of a proper tool grinder (another project) I hand-ground a cutter for
the rack tooth (0.1 mm at the bottom) from a rod of high-speed steel.
For holding this tool-bit in the shaper, the old lantern-style tool
holder from the watch lathe came very handy. The unwanted parts of the
ring were cut away on the shaper using ordinary left and right hand
lathe tools. Finally the necessary sections were trimmed off with a
fine saw blade on the lathe's sawing table.
The gun barrel and lock
March
2007 - Again, because there will various visible areas
of bare metal, the
material of the original, that is steel, was chosen. A piece of
round bar was faced, centred and rough drilled for the bore. This hole
served as a protective counter bore for the tailstock centre during the
following turning operations. In order to get a good roughening finish
the automatic feed was set up. Unfortunately the minimum feed per
revolution on the watchmaking lathes is still too high to get a
'mirror' finish. One day I have to construct some sort of reduction
gear. The outer part of the barrel has slight taper (1 degree included
angle) and the top-slide was off-set for this operation. For rounding
off the ends of the rings the LS&Co. hand tool rest came to good
use. The work was finished off with fine wet-and-dry paper (remember to
cover ways!) and steel wool. The bore was bored to diameter using the
slide-rest and micro-boring tool. I had originally envisaged to also
show the rifling, but a quick calculation told me that for a 1 mm bore
and 72 rifled fields I would need a tool edge just over 0.04 mm wide ...
For drilling holes for the trunnions
and milling the seat of the
lock the diving head was set up on the slide-rest. I could have done
this operation on the milling machine, but on the lathe the dividing
head is centred automatically. The outer end of the barrel was
supported by the arm with an appropriate centre fitted. The resulting
shape from the milling operation looks like a keyhole, but something
like a mushroom shape with sharp edges is required. This was achieved
by hand filing. For the next operation the set-up had to be transferred
to the mill anyway: milling the seats for the square trunnions. The
trunnions merge in a concave curve with the barrel. The trunnions were
turned up on the lathe as disk with two round stubs protruding from
either end. In the dividing head on the mill the disk was milled square
to the size of the seat (or rather the other way round). These parts
then were soft-soldered to the barrel. Back on the mill the concave
curves of the square part of the trunnion were milled using a miniature
ball-head cutter, rotating the barrel in the dividing head.
Aiming a gun in these days was a
rather primitive affair, using just
simple sights. The sights (two of them on either side of the barrel)
consisted essentially of a round bar with a sliding rod to give the
elevation. The beads (mounted near the trunnions) were observed through
a ring of inverted U-shape on top of the rod. The bar was screwed into
a notch in the barrel. Now, drilling into a round at a tangent is
nearly impossible without deflection and breaking the drill (0.3 mm!).
Therefore, I ground flat a broken drill bit to make a make-shift
micro-mill and sunk a start hole. This was finished with an ordinary
drill.
The next
thing to be tackled was the
lock piece. This 'wedge' has a rather complex shape with a flat front,
but a round back and various recesses and cut-out. I decided it would
be best to undertake most of the machining operations while it is still
attached to some (round) material that can be easily hold in a collet.
The round back was milled on the mill's rotary table after the various
coaxial holes had been drilled and the flat sides milled, all in the
same set-up. For machining the other recesses the piece had to
transferred to the diving head on the mill. The large ring was also
turned up and two holes drilled into it for seating the circular rack
that forms part of the elevating gear.
The most
time consuming part turned out to be the cover piece for the
lock, which in the prototype was fastened by five hexagonal head bolts.
It holds the moving and locking screws in their place. It took me four
tries before I produced a half-way satisfactory piece. Soldering the
microscopic bolts (0.4 mm head diameter) in place got me quite a few
grey hairs. Finally a fake locking screw was turned up and the moving
screw, which moves the lock in and out, was faked from a couple of
drilled-together 0.1 mm copper wires, covered in a thin layer of solder
to make them look like steel.
The various parts of the lock were assembled using lacquer and
cyanoacrylate glue.
The upper carriage
Throughout 2008 - Much
time has been spent on re-drawing the carriage as templates
for etched parts. After the etching process has been more or less
'mastered', surface etched parts of sufficient quality were produced.
February 2009 -
The side pieces have been assembled. A filler was sawn from 0.8 mm
brass sheet and the etched covers soldered on. Then 'rivetted
angle-irons', from etched parts were soldered on. These will connected
by tie-plates. The frame is also strengthend by horizontal ties. These
are composites from several etched parts in order to show the
rivetting. The horizontal ties were soldered to the side pieces, while
the bulkhead-like ties were glued in because it would have been to
difficult and risky to bring the heat for soldering at the right
places. The covers for the trunnion-bearings were bent from an etched
part and soldered together.
The upper carriage was further
kitted-out with wheels, the
gears etc.
The front and rear rollers were turned from steel to give them a real
'steel' appearance. On the prototype the rear rollers sit in excentric
bearings that allows them to be brought into to contact with the rails
on the lower carriage: when being fired the upper carriage slides back
on these rails, the rollers allow it to roll back into the firing
position.
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Assembled
carriage from the rear
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Assmbled
carriage from the front
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Carriage with
the barrel in place. Note the trunnion bearings cover (not yet trimmed
to lenght)
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Added the
rollers plus the sockets aft for the lever that is used to turn the
excentric bearings of the rear rollers
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March 2009 - The
gears were cut from brass stock in the milling machine
with the help of direct dividing head and different division plates.
The shape of the teeth is not exactly correct, because I used a
disc-shaped burr as cutting tool. However, at this module (0.06), where
the teeths are merely pitched 0.1 mm apart, this is hardly noticeable.
The gear wheels are parted off from the stock on the lathe. The gear
segment that will be attached to the barrel was produced in the same
manner.
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Cutting the
gears for the gun elevating mechanism using different division plates
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to be continued ...
Deck
Furniture
Bollards
May 2007 -
The ships was fitted with four pairs of bollards of square cross
section; two at the rear and two on the raised quarterdeck. Luckily a
good rather close-up photograph of the real specimen is available (see
main page). The bollards are milled from round brass stock. Round stock
was chosen as a starting point rather than e.g. flat stock, because it
can be held easily in the lathe for turning a spigot on which, by which
the part can be held for further machining. Otherwise it would be
difficult to mount such small a part on the miller for machining five
sides. The spigot is also a convenient reference for machining and for
fastening on the model eventually. From the lathe the raw part is
transferred to the dividing head mounted on the milling machine. After
each pass with the tool, the part is turned by 90º or 180º
depending on requirements. Thus a square and symmetric part is
produced. For a final machining step the part is transferred back to
the lathe and the dome shaped head formed using a very fine file on a
roller-filing rest. The job is completed by rounding off the corners
using a not-too-hard rubber-bonded abrasive wheel (CRATEX)
in the mini-drill. Remaining machining burrs are removed by offering
the part to wire brush wheel.
September 2008 -
The base for the double bollards were intended to be a surface etched
parts, but I was not happy with the results. So I decided to make them
from solid brass. Solid brass was easier to handle for machining than
brass sheet. Nevertheless the envisaged machining operations prompted
me to make a couple of gadgets, fixtures, for the mill and the lathe.
Milling around the edges or on top of flat material always presents
work-holding problems. Worse, if several identical parts have to be
produced. Hence I divined a work-holding block with several clamps and
stops running in a T-slot. Similarly holding small parts for cutting
off on the circular is tricky and best be done on the lathe with
special saw table clamped to the top-slide. This saw table allows parts
to be clamped down for cutting.
The three parts of the bollards were soft-soldered together.
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Drilling
set-up
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Milling
the beading
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Sawing
off surplus material
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Parting
off the individual bases
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Milling
a bevel
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Parts
of double bollards
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Work
holding
for soldering
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Bollards,
chain stoppers and spill
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Chain-stoppers
May
2007 - One pair of chain stoppers is located immediately
behind the hawse
pipes as usual. A second pair is placed above the chain locker, which
is located immediately in from of the armoured barbette. The bodies of
the stoppers are rather complex castings, calling for some complex
machining operations in model reproduction. The same basic technique as
for the bollards was used. Given the complex shape, however, machining
is not possible in one set-up. for certain operations the axis of the
spigot has to be perpendicular to the milling machine, while for
others, such as drilling it has to be parallel. For the latter and for
milling the various slots, I choose to transfer the dividing head to
the lathe. This has the advantage that its centre line is at the centre
of the lathe spindle.
The slots were milled using a micro-tool made from a broken carbide
drill, the end of which was ground flat. This results in a non-ideal
clearance of 0º, while the cutting angle and side rake are that of
the original drill bit. However, not much metal is removed so that this
doesn't really matter here.
One set of stoppers was milled from brass, while for the other one I
used PMMA (PLEXIGLAS®, PERSPEX),
the main reason being that I ran out of brass stock. However, genuine PLEXIGLAS®, is pleasant material to machine and easy on the
tools. It holds sharp edges and it easier to see what you are doing
than on the shiny brass. Acrylic paints seem to key-in well - basically
its the same molecule, of course. On the downside one may note that
small and thin parts are rather brittle. Using diamond-cut carbide
tools gives a nice smooth finish, but normal CV- or HSS-tools can also
be used, of course.
While for the bollards and the front pair of stoppers the spigot could
be on the geometric centre of the part, making it easy to measure while
machining, for the after stoppers I had to place the spigot to the
centre of the pipe down to the locker, so that the concentric rounded
edges could be milled. The pictures show this operation.
October
2008 - The stoppers have now completed with etched brass
releasing
levers, etc. The fore stoppers were also soldered to surface etched
base plates.
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| Undercutting
using a micro saw bit |
Stoppers
compared against a 5 Euro-Cent coin |
Drilling
the hole for the release lever
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Finished
after stopper
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Etched
fret with stopper base plates (bottom left) and levers (bottom right)
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Finished
fore and after stoppers (right column)
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Anchor
capstan
August
2007 - One component that always has puzzled me somewhat
as to their
manufacture in a model has been the sprocket on capstans. While the
geometry on horizontal windlasses is quite simple, with suitable
depressions for the chain links around the circumference, the sprocket
on a capstan is a complex affair. In any case the capstan head cannot
be manufactured in one piece. So I broke it down into three pieces: the
spill head, the sprocket and the base drum with the pawls. The whole
capstan has more pieces including four guiding rollers and a finger to
pull the chain off the sprocket. The cast base on the prototype will be
reproduced as a surface-etched part.
The sprocket started out as a 2.5 mm brass rod taken into the dividing
and into five notches were milled to produce something like a
five-pointed star (these sprockets typically have five or six arms).
The notches for the horizontal links were cut on the lathe with a
forming tool. The sprocket then was faced and drilled to fit onto the
capstan stem. The next step is cutting it off. This produces some burrs
that need to be taken off. Luckily I have collected over the years
almost every type of work-holding device that was ever made for the
watchmakers lathe. Here the insert jewel chucks came handy to hold the
2.2 mm by 0.6 mm sprocket for facing-off.
The capstan head is a simple turning job. The curved surfaces are
pre-cut with appropriate lathe tools and then finished with very fine
files. Incidentally, the implement shown on the appropriate picture is
a rare miniature micrometer, also coming from the watchmakers toolbox
and very handy for measuring narrow recesses and the likes. They came
in sets of three, the other two are a depth-micrometer and one for
measuring the width of notches respectively.
Finally, the three parts are soft-soldered together.
September 2008 - Again
the guiding rollers are a simple turning job. The shapes were produced
with a free-turning graver and by rotary milling in the dividing head.
In the meantime various etched parts had been produced, including the
base plate made up of two different superimposed parts and minuscule
pawls. Also a chain separator from 0.3 mm copper wire rolled flat was
produced. The various parts were soldered together.
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Assembled
capstan head
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Shaping
the head of the rollers by rotary milling
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Set-up
for shaping the rollers using the geared dividing head
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Etched
fret with capstan base plate (top left) and pawl (bottom centre) |
Finished
Capstan (bottom left)
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Skylights, Companionways
etc.
September/October
2008 - The basic structure of the skylights etc. consists of
strips of Pertinax that are cemented together with cyanoacrylate glue.
More intricate parts are etched from brass. In the past I have
constructed the skylights around a piece of Plexiglas milled to the
right shape. It was not possible here, as the skylights will have to
painted to represent wood, while the bars will brass colour. It would
have not been possible to mask the Plexiglas for the spray painting.
Hence, the frame of the engine room
skylight consists of a an etched brass part, folded up and
soldered together. On the inside grooves had been etched in that serve
to locate the bars to made from thin copper wire. The lower frame was
constructed from Pertinax. The wooden gratings on both sides of the
lower frame are again etched parts. Once this structure was complete, a
square block of the size of the footprint of the skylight was milled
from a piece of Plexiglas. In the next step the roof-shaped faces were
milled on. To this end, a small insert vice was set to the appropriate
angle of 40° in a larger vice bolted to the mill table. The fixed
jaw of the insert vice pointed upward and the side of the block to be
milled rested against it. This ensured that all four inclined faces
would have the same angle and would start from the same height with
respect to the reference (bottom) face of the block. A very smooth
surface with little tool marks can be achieved on Plexiglas. The final
polishing of the surfaces was done using CRATEX-type drum polishers
followed by a felt drum loaded with polishing paste. All in the same
vice setting to ensure a flat surface. I was lucky the Plexiglas
'house' fitted like a plug into the skylight frame.
The prototype construction of the boiler
room skylight is not completely clear from the drawings, so that
I had to 'fudge' it a bit. First the central piece that supports the
chimney was shaped from a piece of Plexiglas. The PROXXON drilling
machine was abused as a milling machine to this end: a diamond-cut
milling bit was taken up into a collet and the height of the machine
set so that the bit reached just below the table. Now the Plexiglas
part was passed free-hand along the mill. The form to be cut out was
printed on a piece of paper that was stuck to the Plexiglas. It was
tested against the shape of the etched grilles in order ensure a snug
fit. The box around the skylight was constructed again from Pertinax.
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Etched
parts for the skylights.
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Shaping
the central part for the boiler room skylight
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The
completed boiler room skylight
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Unglazed
framework for the engine room skylight
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Squaring
up a Plexiglas block for the skylight
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Milling
the sloping faces
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Polishing
the sloping faces |
Finished
Plexiglas 'glazing' block
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Glazed
engine room skylight
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Thoughts on Etched Parts
Some
people refer to the process of making photo-etched parts as chemical
milling and that is the way I view it; a process to cut out and shape
parts that are too small or otherwise to delicate to handle
conveniently with other manufacturing processes. Unfortunately, the
employment of this process moves much of the modelling work onto the
computer, as the patterns or masks now are produced with the help of a
drafting program. These masks are largely developed by scaling the
contemporary drawings and drawing the respective part over it in a
different layer. These parts are then composed into the actual mask. Of
course, 'left' and 'right' sides have to be drawn separately, if the
part is to receive surface-etched detail. A strict procedure of copying
and mirroring has to be adhered to in order to achieve a perfect
line-up. Much thinking has to go into the best shape of parts and some
experimentation. The etching process is not so well controllable, as a
machine tool, at least in the simple set-up I am using. The best
thickness of interlocking slots or the drawing size to achieve cut-outs
of a specific dimension and similar features have to be found by trial
and errors sometimes. Literary it is often 'back to the drawing board'.
This set-up is only suitable for dip-etching. Commercial companies use
foam or spray etching, which work faster and produce less undercut. I
decided to work with very small 'frets' only, the size of one or two
large stamps. This reduces the cost of material, if something goes
wrong and the smaller size seems to make it easier to get uniform
results over the whole 'fret'. I bought second hand a UV-source for
exposing printed circuit board. It has a timer and hence makes the
process more repeatable. The developing and etching vessels are
plastic film tins, coming from the standard film rolls (don't get any
new ones since I have switched to digital, of course). The brass is
bought in a ready-sensitised state, so no messing about with
UV-sensitive lacquer is needed. Much experimentation went into a
suitable way of making the masks. Eventually a newly bought ink-jet
printer produced sufficiently uniform print-outs on overhead
foil, but the resulting masks are not really perfect. However, I did
not want to go a commercial photo lithography company
for them.
To be continued ... watch this
space !
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