Heating must be done very slowly and be turned off long before the tubing has settled to the proper depth to avoid excessive melt out. (Note: This rig can heavily overload the power supply so transformer heating must be monitored with special care.) We have just begun to explore other interesting applications. It is possible, for instance, to blank against a form rotate a styrofoam knife and thus fabricate turned shapes such as vases and newels. An experimental hot wire "lathe" is shown in Fig. 10. The ridging is caused by the fact that this block is made up from 1" layers which are at right angles to the direction of the knife through the milling machine by simply clamping the two halves together and carefully drilling the joint. 6Allied Electronics (1973 catalogue) lists a Triad filament transformer (Mfg. # F-2SUI with a 7.5/6.3 volt secondary rated at 25 amps for $33.27 each. Allied sells a 5 volt filament transfo rmer under its own name rated @ 30A for $1S.90 (Mfg. #6KS5VGl. This would probably work in most instances. Alternatively one could wire the autotransformer in such a way as to deliver 135V to the stepdown transformers by using the "20V" tap available on many types. This should give an open circuit voltage of approx. 5.6V which should be close enough. 7Ventilation should be somewhat more effective in the open frame types specified in footnote 6 than in the potted style we used. - material. Ridges are easily removed by hand sanding but represent a persistent difficulty any time built up thicknesses are cut with the form hot wire. The severity of the ridges are reduced by orienting the layers parallel to the direction of cutting. See, for example, Fig. 3. Other potentials remain to be explored. For example, would a different knife cross section be better in some applications? For instance, would flat stock knives with the broad dimension parallel to the direction of travel give a smoother cut? Are there better ways to control heating in the imbedding procedure? These and other possibil ities present a fascinating group of techniques yet to be explored. I would like to take this opportunity to thank the Dow Chemical Co. for donating much of the styrofoam used in these experiments. NOTES 1 The only vendor of several contacted which was able to supply large gauge nichrome wire was the Kanthal Corp. of Bethel, Conn. Their minimum order for any single item is $100.00. Sizes heavier than B & 5 #S are a special order item and thus require a 3-4 mo. delivery time. Small quantities of 14 and smaller gauges are marketed through scientific supply houses such as E. H. Sargent & Co. Figure 11. The curved moulding of this header was fabricated with a set-up like that shown in Fig. 6. Figure 12. This octagonal newel was cut out in about 20 minutes using the lathe rig shown in Fig. 10. For this project the work piece was locked in place and the form knife (shown as the lower item in Fig. 7) was slid past it. The styrofoam was then rotated 1/8 of a turn again locked in position and the process repeated. This was continued until all sides were shaped. Zit should be noted that the large power supply to be described for use with heavy gauge knives is entirely compatible as a supply for light gauge nichrome though it is far larger than required in the latter application. 3The 100% or more overload is tolerated by limiting the duty cycle. The surface temperature of the individual potted transformer cases rose about 45°F in a test period of one hour with a load of 150 A. Thus a utilization period of reasonable duration can be achieved. (Some adjustment may have to be made in this depending on the particular transformers used.! 4 Actual measured voltages under load will be considerably lower because of internal resistance in the transformers. For instance, under a typical operating load of 150 A the voltage drop across the knife is approximately 1.5 volts whereas the open circuit voltage measured at the power supply output with the same autotransformer setting is approximately 2.5 volts. sThe construction of the clamps was based somewhat on available stock materials consisting of sections of 1 1/2" x 1/2" bar stock the lower of which was brazed to a 1/S" x 3" x 7" base plate. The 1/4" bolts used to close the clamp should be arranged in parallel pairs rather than the staggered arrangement shown. An adequate 15/64" dia. groove for the knife can be cut without a ~ THEATRE DESIGN AND TECHNOLOGY DECEMBER. 1973 13