- December 2004
- Haynes, Fred (Society member)
- Naval technology
- None noted.
- Originally published in the Naval Historical Review edition (all rights reserved)
In 1959 as an apprentice Scientific Instrument Maker in the Optical Workshop at Garden Island Dockyard I learnt to use these materials as part of my trade.
The use of optical devices such as telescopes, binoculars sextants theodolites and rangefinders by the Navy was to aid practical watchkeeping, navigation, hydrography, and gunnery. All these instruments were repaired during their service use utilising a range of miscellaneous materials.
Beetles, trees, birds and spiders all provided the raw materials for returning these unserviceable items to ‘as new’ condition, ready for re-issue to the Fleet.
When first starting in the Optical Shop one of the first items issued by the storeman, along with a wooden box to keep optical cleaning equipment, was a screw top jar. This is where beetles became an essential part of an Instrument Makers toolbox. In this jar was mixed a thick soup of shellac, a secretion of the Lac Beetle (Tachardia lacca), and methylated spirit.
By the time the apprenticeship was completed this mixture had developed into an evil brew, jealously guarded by its owner. It became the universal glue, used for anything, from sticking bits of chart paper packing around lenses, to holding tin foil spots onto prisms for adjustment. It was even used to secure graticule wires in some sextant telescopes.
Sometimes after thinning down with rectified spirit (alcohol used for cleaning optical components) it was used for its more conventional use of rudimentary French polishing of an instrument case. After this exercise the lid was left off the jar for several days to allow the excess alchol to evaporate, and the brew soon returned to the usual Vegemite consistency.
One of the older tradesman in the workshop boasted of having had the same shellac jar for twenty years ‘man and boy’. He obviously ignored the fact that after this period of time there was not much of the original mix left. It had become just like the proverbial hundred-year-old axe that had only had three heads and five handles.
Trees were certainly used to provide the wood for various stowage boxes for optical instruments. However from the early 1800s resin obtained from the bark of balsam fir trees (Abies balsamea), found in North America, was collected and refined for many uses, including assembly of optical components. Optical cement has to have a refractive index similar to glass so that it becomes invisible when looking through the instrument.
Canada Balsam, as it was known, continued to be used to cement lens and prism elements together even after synthetic optical cements were developed.
Prisms combinations fitted to binoculars and rangefinders were assembled in a jig and baked in an oven until the balsam set. When the instruments were tested for collimation and errors were found to be outside the range for mechanical adjustment the prisms could be reheated and adjustments made.
Of course with experience you learnt to get adjustment right the first time thus avoiding the need for movement after the ‘first bake’. With all adjustments for collimation and focus satisfactorily completed the prism combinations were again removed and placed in the jig for their ‘final bake’. After the final bake all excess balsam was removed and the prisms given an optical clean.
Most modern two part cements do not offer this ‘readjustment if not right’ feature, giving only one go to get it right. Perhaps the nearest to balsam is the ultra-violet setting cement, similar to that now used by dentists. The light is used to harden the cement and by giving a limited exposure one is still able to carry out limited adjustment before full exposure. Canada balsam is still used to prepare microscope slides.
Scientific Instrument Makers at work in Garden Island Dockyard’s Optical Workshop.
Probably the most exacting operation to perform on optical instruments was to clean the graticule or field lens. This is usually the one optical surface in critical focus, and as such any dust contamination appears as black spots in the field of view. In the case of submarine periscopes, specks the size of five microns (.00005”) and up become visible. Submarine captains can become very paranoid performing emergency dives after spotting a potential enemy aircraft that always seems to be in the same place in the field of view.
Birds played an important role in the elimination of these specks of dust. Three inch sections of feather quill were sharpened much the same way as the old quill pen nib and these were used to gently pick specks off the lens surface. For more stubborn specks, stuck to the surface due to static charge, the quill was used to sweep them off across the surface of the lens. The softness of the quill ensured that scratching of the glass did not occur and allowed frequent re-sharpening of the pointed end.
Several optical instruments actually had small packets of quills included in the spares carried in their transport box. One of these was the Barr & Stroud metre base rangefinder. Quills even had a Pattern Number and in 1969 could still be ordered from Naval Stores. (0552-972-3673)
Survey instruments such as theodolites used by the Hydrographic branch require extremely fine graticules to enable accurate measurement. Tavistock theodolites still in use in the late 1950s utilised spider web to provide filaments for their graticule. Web is the ideal material for this purpose because of its fineness and strength. One optical design handbook even describes how web can be unravelled, just like a piece of rope, to obtain individual strands of extreme fineness. When the web is stretched across the graticule holder and glued down with shellac, unlike human hair or wire it will not sag due to changes in temperature or humidity.
Of course the initiation into this operation lent itself to the inevitable reverse ‘leg pull’ to the new apprentice. The foreman would instruct the ‘new hand’ to ask the storeman for the ‘spider web tools’. Not sure, he would hesitantly ask for the tools, and would be handed a drawer containing the items along with the same type of screw top jar used for shellac. The tools consisted of several wire frames bent into a square with a handle fitted. When asked what the jar was for the storeman would answer ‘to keep the spider in’. By now the apprentice would be sure that it was all an elaborate joke, but he soon learnt otherwise.
After catching a suitable spider from the outside wall of the workshop, or amongst the bushes on the northern hill of the Island, he learnt how to collect the web on the frames.
Placing the spider on the top of the frame it was prodded until it did a ‘bungee jump’, and as it fell its web would be wound onto the frame by rotating the handle. With the spider safely back in the jar the web was washed with alcohol to remove the globules of sticky glue. When dry the web could be laid across the graticule holder and cemented in position. The final operation was to find a nice fat fly for the spider as a reward. Some spiders lived for up to six months in their screw top home.
Spider web was one of those items not held by Naval stores, but we would often say that they had plenty on their shelves, if only we could find the Pattern Number to order it.
These are only a few of the miscellaneous items in the Optical Instrument Makers toolbox. There were others such as hair, handkerchiefs, pitch and cork, but that’s another story . . . .
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