The VHRC core is a film type honeycomb core. The copper material (film) is supplied in a roll and is manufactured in Sweden by Luvata. It must conform to strict specifications, some of which are tensile strength, yield, thickness, elongation and hardness. The width of the roll dictates the thickness of the core being made.

The film is run through a bath of pressing and forming oil before being entering the press. The press stamps 2 copper strips at a time, one on top of the other. A series of dimples also are pressed into the film to assist in the assembly of the core.

The die-set within the machine, stamps 3 simple corrugations repeatedly into the copper film as it passes through the dies towards the indexed guillotine. The film is stamped and moved forward using the "cam action" of the lower set of dies.

The hand operated indexed guillotine cuts the film to length, to suit the core being made, with an allowance being made for the lock-seams, top and bottom. (See height chart)

The next step is to lock-seam the stamped strips to form a tube. Both ends of the strip are lock-seamed in two separate actions. The lock-seam forms the flat surface on the top and bottom of the core to which the tanks are soldered.

The tubes, then, have a single strip slipped between them to form the fin. Once the fin is fitted, the core is stacked on the flat assembly table to the required width, clamped and face dipped in molten solder 6mm deep.

When a honeycomb core has a non-square shape, the corners must be reduced in steps.

The tubes are made shorter to form the correct shape, and timber fillers are used to hold the core together during assembling and dipping. To avoid being immersed in liquid flux prior to dipping, the timber fillers are narrower than the core depth. This also ensures they stay out of the molten solder bath.

Once the core is dipped and the frames removed, the tubes are shaped to match the tapered tank using light hammer blows.