266 moves in the x direction by pushing on slide bar 290 on spider 162 and slides in the x direction on a single slide rod 294 that extends between the bottom of slide block 146 and the top of spider 162 rod 294 is secured to a bracket 296 on the bottom of upper arm 12 movement in the y direction of slide block 146 along slide rods 148 150 is accomplished in substantially the same manner just described a third mounting bracket 280 is supported between mounting brackets 250 252 and supports the y direction reversible stepping motor 282 thereon the y direction motor shaft is coupled to drive shaft 284 and is rotatably supported at its right by upper arm 12 a second drive strap 286 is secured to y drive shaft 284 for moving slide 114 in response to commands sent to the y direction motor 282 by the programmed control system drive strap 286 is identical to strap 262 of fig5 b and operates in the same manner as described above to provide accurate programmed movement to y slide 146 the details of channel shaped lower arm 16 are best seen in fig6 and 7 lower arm 16 is made from a short length of channel shaped metal whose top edges are machined to form the dovetail notches 202 204 which are adapted to slidingly receive therebetween the cover plate 28 a plate is secured to the right end of bottom arm 16 and is provided with suitable means such as bolts to rigidly attach arm 16 to a wall of vertical arm 14 bottom arm 16 has a pair of parallel slides 206 208 secured to its inside bottom surface slides 206 208 have top slide surfaces 206a and 208a and have.