In the days before CAD software, designers and technical draughtsmen had to commit each and every part to tracing paper. MANN+HUMMEL was no exception here, with every individual part meticulously hand-drawn, labelled and marked with dimensions. Back then, pen, paper and ruler were the tools that allowed the designers to express themselves through their drawings. Construction drawings were internationally standardised, allowing them to be understood all over the world.

Here at MANN+HUMMEL’s Speyer location, we are still in possession of many of these original drawings. The oldest of these dates back to the Second World War (26 March 1945), and depicts something referred to as a “lower clamping piece”, which was used in the pressing of strainer disk packs.

At that time – before the invention of spin-on filters – MANN+HUMMEL manufactured re-usable filters featuring sieve cloths equipped with wire-wound slotted tubes or plate gap filters. They were not disposed of after use: instead, the insert was removed and brushed clean using white spirit, before being reinserted. These re-usable filters were intended for use in any gearbox or hydraulic system which demanded a certain basic level of oil purity. In contrast to the purity levels offered by today’s paper filters, strainer, slotted tube and plate gap filters were only able to achieve relatively rough filtration of around 30 to 100 µm. Although production has since moved over to a supplier, MANN+HUMMEL continues to sell such filters in small order volumes today, as there are still a small number of automotive parts suppliers who require filters like these for old (and a few new) gearboxes.

Another drawing, dated 28 June 1957, shows a permanent magnet – these were once frequently deployed alongside re-usable filters. Fastened to the dirty side of the filter insert, they were used to fish rough metal elements and chips out of the oil. This was necessary as the gears in old gearboxes were not as precise as they are today and lacked sufficient synchronisation. Ventilation introduced additional particles into the gearbox and, crucially, the residual dirt could not always be entirely removed by washing the machined parts. This was the magnet’s time to shine.

Yet another drawing, this time dated 1956, depicts a drain plug which was used to drain oil from a filter reservoir. To help preserve the original drawings, they were bordered with either a white or red knurled strip, with red-bordered drawings being sent out as ‘customer drawings’. At some stage, the drawings were microfilmed and they were later entered into the CIM Database. When I joined the company back in 1988, we had our own department which worked with the drawings. Every change was precisely documented, duplicated and distributed throughout the organisation, and since there was a corresponding microfilm slide for each drawing, these were used to note which part each component was built into.

IT has changed a great many things since then. Today, designers are supported in their work by CAD systems: they create 3D models, extrapolate scale drawings, calculate the stresses that will act on a part during operation, and much more. Gone are the technical draughtsmen – it is now CAD experts who provide professional support to designers. What’s more, with so many different CAD systems to master, their remit is significantly more challenging than that of their predecessors. Neither the old drawings or the microfilms are compatible with our modern Catia 5 CAD system, so their only purpose now is to serve as a (beautiful) reminder of a bygone era.