BUILD YOUR OWN VACUUM HOT TABLE FOR $600
Reginald M. Hoare, & Susan J. Connell
THERE ARE PROBABLY several improvements or alterations that can be made on this basic design, depending on the preferences of each individual conservator. Certainly we would like to hear of a good source of latex, and although we rarely find any need for the thermostat, undoubtedly a more reliable method for securing it would be preferable. Some conservators might prefer to have the vacuum drawn through the membrane on the surface8 and also add exhaust fans around the sides to speed the cooling process.
On the plus side, the table is simplicity itself; all the working parts are easily available for repair, and the whole thing can quickly be dismantled for moving. Others may wish to experiment with the height of the shelf, and the position of the bulbs. If a plain piece of linen, impregnated with wax, is laid on the table it is possible to see at a glance, as the wax starts to melt, if the bulbs need adjusting. It may be advisable to place the bulbs slightly nearer the edge of the table as there is more rapid cooling there, while still allowing the heat from each bulb to overlap, so there will be no hot or cold spots. Certainly with this system there is none of the washboard effect, which is sometimes a characteristic of the conventional heating elements. As for the position of the shelf, we have found that 15″ – 16″ between the top of the bulbs and the underneath surface of the aluminum seems to be just right for 18 lamps under a 4′ × 8′ table; and as can be seen by the graph the table heats up and cools down quite rapidly. Theoretically it should be possible to place the bulbs at just the right distance to make it impossible to overheat, but it might take a bit longer to reach the required temperature. If anyone wished to pursue this theory, the exact distance from bulb to aluminum, for even heating could probably be worked out by a heating engineer.
To sum up, we think that this vacuum hot-table, apart from its cheapness, is an attractive proposition because of its safety, relative speed in cooling, and accessibility for repairs.