and nuts. The 3/8" th ickness was used to provide a reasonably broad bearing surface for the admittedly crude steel on steel spindle shaft bearings and to provide adequate frame rigidity. Notice that it is not necessary for the frame to support the cantilevered spindles under the working stress of bending the tubing since working in combination with the removable spindle stiffeners (seen on top of the forming rollers in Figure 1 and in profile in Figure 3) the bottom bearing plate is not loaded by the pipe being bent. The spindle shafts are made longer than required by the rollers themselves to accommodate the stiffeners. The top end of the center spindle shaft is drilled and tapped for a 1/4" bolt which with a washer holds the stiffeners in place except when changing rollers. Figure 1 Top view of bender built by the author with a length of thinwall tubing being bent. THE DRIVE TRAIN For proper movement of the tubing through the bender all three rollers must be rotated at the same speed-one clockwise and two counterclockwise. To provide this motion three identical 4" pitch diameter spur gears were used (see Figure 3). Heavy 3/4" face gears were used as a hedge against less than optimum shaft alignment. Figure 2 Basic bender mechanism stiffeners removed. with top and spindle Several steps of reduction were necessary. The first step consisted of a 2-1/2" pitch diameter spur gear mounted on a shaft driven by a 12" diameter pulley (see Figure 4). This combination helped reduce traction levels to someth ing that cou ld be handled by V belts. The 12" V pulley was driven by a 2" pulley on a second countershaft again mounted on the main frame. The final step was achieved with a 5-1/2J' pulley on the second counter shaft and a 1-1/2" pulley on the motor. The 1/3 HP motor salvaged from a wash ing mach ine was suspended from the main frame on a section of 1-1/2" x 1-1/2" x 1/4" angle iron. This was bolted to a heavy bracket which was in turn bolted to the bottom plate of the stationary frame (see Figure 4). The details of this mounting will vary somewhat with the motor used and thus the motor mount is not shown in detail in the working drawings. BEL T TIGHTENERS Figure 3 Detail view of rollers, stiffeners and gear drive. 26 C§IJ Maintaining sufficient belt tension proved to be something of a problem. The small belt from the motor was tightened by utilizing the original pivot mount on the motor and a piece of threaded bar stock and nuts to provide adjustment. The belt to the 12" pulley presented more difficulty because the positions of both shafts were fixed. The solution used was somewhat crude but effective nonetheless. A 2-1/2" diameter fixed caster was hinged in such a way as to press against the outside of the belt. Before installation, however, the caster was "turned" using a drill press and a file to change the cross-sectional profile of the edge from convex to slightly concave in order to improve its tracking on the belt (Figure 4). THEATRE DESIGN AND TECHNOLOGY DECEMBER. 1972