Cropico in the 1960s

A short history of the early days by Dr  Malcolm Dye MIEE (son of one of the founders) who worked there in his summer vacations in the 1960s when it was thriving.


The Croydon Precision Instrument Company was founded at the beginning of the 1950s when Fred Dye (my father) and Warren Potter were financially backed by Mr P.A. Bovey.  Mr Bovey had financial interests in other manufacturing companies, some of them in the area of Thornton Heath on the outskirts of Croydon, and it is probable that he helped to find the first premises in Union Road.  This was a draughty victorian workshop beside a cobbled yard,but good enough to get the company started.  At that time there was plenty of demand for instruments for measuring electrical resistance, especially from telephone companies and for instruments for measuring thermocouple emfs for monitoring industrial processes.  The Cropico products followed others on the market, but with emphasis on delivering high quality instruments.  Fred Dye was both factory manager, and the product design engineer.  Warren Potter was marketing and sales.

The company outgrew the old workshop and moved round the corner to Hampton Road to occupy half of a factory used for coachwork repairs.  To separate the bus repairs from the precision instrument manufacturing an 8 foot high partition was erected across the middle of the building.  Soon the partition came down and Cropico occupied the whole factory.  By the early 1960s the founders had bought into the company (later to buy it outright) and there were two dozen employees kept busy 5 days each week.

Most of the products were based on a common set of components that were mostly produced in-house.  The rotary selector switches and the bobbins for the resistance coils were common parts used in almost every product. A typical decade resitance box started life as a sheet of Paxolin about 5mm thick, cut accurately to size with milled edges and jig-drilled with more than a hundred holes.  Many of the holes were for the contacts of the rotary switches that were built on the panel.  Each switch needed 20 contacts, so a 4-dial box needed 80.  Each contact was turned on a capstan lathe (later an automated lathe), producing items that looked like an unslotted cheese-head machine screw with a solder cup at the end. These were inserted in the panel and held in place with nuts on the back.  Each switch needed two arcs of contacts so that the moving leaf-spring contact on the centre spindle would bridge successive pairs – one on each arc. A centre bearing, spindle with detent disk and contact spring completed each 10-position switch.

Elsewhere in the factory the resistance coils were produced.  Plastic bobbins were non-inductively wound with manganin wire on a simple winding machine then varnished and set out on spiked trays to be “adjusted”.  Each person working on coil adjusting was equipped with a resistance bridge with spot galvanometer and the technique was to scrape the wire ends clean and insert them into the contact clamps of the bridge and to find a length where the resistance was slightly low. A small machine ran continously steadily forming and cutting solder tags that were inserted in slots at the end of the bobbins. After soldering the tags on, the adjuster had to check the resistance, and slighly increase it by gently filing the last turn of wire to get the spot-on value. The coils were then varnished and put in the oven to be baked for several days as pre-ageing.

 Assembly of the resistance box would have started off  with soldering lengths of tinned copper wire into the swich contacts and bolting the correct resistance coils to the panel around each switch.  A neat job of connecting the coils was required.  The tinned copper wire was bent precisely and covered with yellow “systoflex” before final soldering.  Electric soldering irons were not popular as the lead was a nuisance.  Instead the factory workers made soldering irons out of short lengths of solid copper rod screwed to a thin steel rod.  The copper “business end” was placed in a bunsen burner flame with the steel rod “handle” resting across a “chemistry lab” tripod.  Experience soon taught accurate temperature control by an occasional glance at the colour of the copper.

 Each instrument was finished off by adding pillars to the corners of the paxolin panel and fixing the engraved aluminium battleship-grey top panel on, then the knobs.  Most of the early production was housed in high quality wooden cases that were supplied by a local craftsman.  These were South American hardwood with dovetailed or “combed” corner joints  secured with brass countersunk woodscrews.  All the screw-slots were aligned and the screw heads ground flush with the wood.  The boxes were brought to a high gloss by the in-house french polisher.  This was a real character – a short stocky one-armed scot who had fairly frequent epileptic fits but often had all his coleagues rolling around laughing at his jokes.

 The switch technology used for resistance switching was also used in a range of thermocouple selector switches (up to at least 20 -way) that were popular with the CEGB. One or two were on life test for years, being driven around by geared motors.  The motors wore out and were replaced several times, and the detent springs wore out, but were legitimately replaced, but I think the swiches continued to give good contact performance until a long time after anyone cared!

 Telephone companies around the world bought huge numbers of decade reistance boxes, and would send their inspectors to do quality audits.  A few samples would be picked out and checked against an NPL – calibrated standard, but most often the inspection consisted of vigorously shaking the box while listening for the rattle of foreign objects or debris inside.  I think they always went away happy.

 Later in the life of the company it was able to buy the premises and rebuilt a run-down annexe to make a showroom and office suite, but Fred Dye continued to occupy his traditional glass-fronted office in the factory where he could keep an eye on activities until he retired when the company was   36 years old. By that time (1988) electronic instruments were more common and Fred Dye had formed an alliance with an East Anglian company for product development and production of electronics for Cropico which continued for many years after.

In 1988 and the company later passed in its entirety to Mr Potter's son Michael who later sold it to Seaward. Both the original premises in Union Road, and the much larger premises round the corner in Hampton Road, Thornton Heath (Croydon) are still there, according to Streetview.

Malcolm said that he often discussed his father's ideas for new products - and that he seemed to be able to come up with unlikely winners.  His most surprising was a portable alternative to the Standard Cell - powered by 18 "D" cells and stable (once re-acclimatised to 20 degrees) to better than 2 microvolts.  That was in the mid-1970s, and it sold to almost every Standards Lab in the World, including Russia and China!