2QO HOME-MADE PROJECTION APPARATUS [Cn. IX 



expect the apparatus to do the work of a machine, and also to 

 supply all of the intelligence to enable it to do so. 



426. Baseboard and track. For the lathe-bed carrying all 

 the apparatus (fig. 121, 159) a flat board about 2 cm. (J/gin.) thick 

 is used for the base. The width and length can be made to suit 

 the apparatus designed. The dimensions for that shown in fig. 

 i58-i59are: Length 125 cm. (4 ft.); width 22.5 cm. (8^ in.). 



The track which serves as a guide to the blocks bearing the differ- 

 ent pieces of apparatus (fig. 121) is best made of two brass tubes or 

 rods 12 mm. (^ in.) in diameter and the full length of the base- 

 board ( 42 6a). 



427. Fixing the track to the baseboard. For this, holes 

 should be bored through the tubes or rods, being careful to have 

 the holes parallel so that there will be no torsion or twist when the 

 tubes are fastened to the board. If rods are used the screw holes 

 must be countersunk. If tubes are used then the upper wall 

 should have a larger hole than the lower and a slender screw driver 

 used, (fig. 159 ts), then the screw head goes through the upper wall 

 and presses against the lower side only. 



One tube or rod is fixed firmly to the base, thus : With a straight 

 edge like a T-square make a straight line on the baseboard where 

 the track is to be laid and then fasten the one track accurately along 

 this line so that it will be perfectly straight. 



Now for the other track lay it as follows : Use apparatus blocks 

 ( 428) near the ends of the baseboard and put the loose rod in 

 place. Press the block down firmly so that the loose track will be 

 forced into the groove. Put screws in the end holes, but do not 

 screw them down firmly. If there arc intermediate holes as in 

 fig. 158-159 move a block near the hole, press it down firmly and 

 then put in a screw, but do not screw it in firmly. 



426a. For the rods, one ean procure the thin, polished or nickeled brass 

 tubing used for railing, or the thick brass tubes used instead of iron tubing. The 

 measurement given means the total diameter. Of course one can use any 

 desired diameter by varying the' size of the V-shaped notches in the apparatus 

 blocks (fig. 158 A) or the position of the cleats (fig. 159). If brass tubing is 

 employed for the track, the size known to the plumber is that of the bore, not 

 the outside diameter. Tubing \vith x ' 4 th or 9'ijtli inch bore answers well. The 

 outside diameters will be 10 and 13.5 mm. (13/32 and 17/32 in.) respectively. 



