texture can also be enhanced by coating all surfaces with flexible adhesive. While the ability to turn out any quantity of ornate linear moulding is certainly a boon to designers, curved mouldings are where the form knife makes its most sig· nificant contribution. While it is perfectly possible for a carpenter to build up a complex linear moulding from simpler stock wood shapes, to curve the same shape would be extremely difficult. However, with the form knife a curved moulding can be made with no more difficulty than a straight one. The usual procedure here is to cut out a blank of the proper radius then use one of the curved edges as a lead surface to guide the styrofoam past the knife (Fig. 6). SOME LESS OBVIOUS APPLICATIONS Very early in its history, the form knife very neatly solved a problem that could otherwise have been quite difficult. The problem was to construct a large globe approximately 30" in diameter. The solution was to bend a piece of 3/8" steel bar stock to form a half circle. The Figure 6. Cutting a curved moulding. The radius of curvature is controlled by the arc of the styrofoam blank before it is molded. ends were straightened so as to be parallel to the circles diameter (Fig. 7). This straightened section was bent again to form a handle. The rod was brazed to suitable heavy wire and connected to the power supply. The short, straight sections at each end of the curve were then strapped to a working surface in such a way that the knife could be arced through 180°. With a semicircular knife arranged to rotate through 180° it was now a simple matter to place a block of styrofoam on the work surface and arc the knife through it to create a nearly perfect hemisphere. Two such shapes were cemented together and dutchmaned to form a globe. A special feature of this knife was that its heat distribution was roughly tailored. Because the maximum heat would be needed at the portion of the arc furthest from the pivot where cutting surface contact would be greatest and because of the relatively high torque near the pivot, it was decided that it would be advisable to generate more heat at the extremity of the arc and allow the area near the pivot to remain relatively cooler. This was accomplished very simply by grinding away some of the rod in the middle half or two thirds of the arc and allowing the portion near the pivots to remain full thickness. Thus by selectively allocating resistance along the length of the knife we had a means of distributing heat in a desired Figure 7. Two large-scale hot knives. The upper knife was used to cut 30" dia. hemispheres. The lower knife was used to cut all but the cap of the newel shown in Fig. 12. pattern. The clustered columns shown in Fig. 8 represent another non-moulding use of the cutter. The shafts of these columns were made with a form knife. Blanks made up to slightly over half the column thickness were cut out with the knife and a pair of them cemented together to form a finished column. Mention of these columns brings up a very interesting appl ication for the hot wire supply. I n order to strengthen ~ THEATRE DESIGN AND TECHNOLOGY Figure 8. Both the shafts of these columns and the molded can· tour of the arches were cut using the form hot wire. DECEMBER. 1973 11