Best practice guidelines for the design, production and presentation of vacuum formed tactile maps

Choice of vacuum forming machine

As the tactile graphics literature provides only a broad outline of the vacuum forming process, a detailed description of the most appropriate methods and materials is included here. The majority of authors have used a machine similar to Clarke's ‘Braille Reproduction 350’ (see Figure 2 [28]) to produce tactile maps [23], [24], [25].

This machine was designed to reproduce braille, and was undoubtedly chosen by other researchers because it was most generally available, and accepted standard size sheets for braille reproduction (280 x 292mm and 280 x 216mm). However when such a machine is used, the plastic sheet is not held taut before heating. PVC foil is draped over a mould before being clamped in place and has to shrink into shape when the vacuum pump is activated at the end of the heating time (PVC foil produced for vacuum forming is designed to be stretched not shrunk). A sample vacuum formed image, included in Hinton [26] (see Figure 3 [29]) and photographs of vacuum formed maps included in Schiff [27] show some ‘billowing’ of the flat areas of the moulded plastic where the foil has not enveloped the mould closely. This ‘billowing’ can interfere with the tactile reading of an image.

A more versatile machine, Clarke's 725 FLB (see Figure 4 [30]), has a forming area of 228 x 432mm and is more suitable for use with thicker gauge plastic than the braille model.

The chosen plastic sheet is clamped taut during the heating cycle, above the level of the platen holding the mould (see Figure 5 [31] ).

When the plastic has softened, the platen is raised so that the mould is pushed into the sheet from below, and so the plastic is stretched locally before the air extraction becomes fully established. Once the platen is fully raised the maximum extraction force is applied (see Figure 6, [32]) and the softened sheet is pulled down over the mould to envelop it closely (see Figure 7).

When the 725-FLB machine is used, there is no ‘billowing’. Moulds several inches high can be reproduced: especially useful for the production of maps of hillsides. The 725-FLB has ceramic heating elements that are controlled in independent zones to give an even heat spread, and the plastic sheet softens uniformly. The movement of the heater hood operates a digital time switch, and so enables precise timing of the cycle.