Popular Science Monthly 



of the large wire nail that acts as a sort 

 of a movable handle. The machine is set 

 when the points of the arrows are exactly 

 opposite. The lower wheel always turns 

 from left to right. It is now ready for 

 adding a column of figures. Take the 

 figures 8, 9, 6, 9, 8, 7, 7, 9, 3 and 2 and 

 add them. Insert the point of the wire 

 nail in the indentation of the lower wheel 

 opposite the number 8 of the board. 

 Pay no attention to the numbers on the 

 wheel until you finish adding. Turn 

 the lower figure wheel with the nail 

 until the point is opposite the guide 

 line. Lift the nail and place the point 

 in the indentation at number 9 of the 

 board and turn the wheel until the nail 

 is opposite the guide line. Again lift 

 the nail, insert the point opposite the 

 number 6 of the board and turn the 

 wheel until the nail is once more opposite 

 the guide line. Add the other figure 

 in the same way. The sum total of the 

 column will appear at the opposite ends 

 of the guide lines, namely, 68. 



The capacity of the machine is 100, 

 but by keeping tally of how many times . 

 the cog number 9 passes the guide line, 

 you can use the machine for any column 

 of figures. This machine is also a sub- 

 tracting machine. To subtract with it, 

 set the upper wheel so that the first 

 digit of the minuend appears at the guide 

 line, and then set the lower wheel so 

 that the second digit of the minuend 

 also appears at the guide line. Now 

 place the nail opposite the subtrahend 

 marked on the board and move the 

 lower wheel clockwise — in the opposite 

 direction to that indicated by the arrow 

 — the number of spaces equal to the sub- 

 trahend. As in addition, the result ap- 

 pears at the guide lines. When there 

 are two digits in the subtrahend place 

 the nail in the hole opposite the digit 

 on the board and, as in the first case, 

 turn the wheel a number of spaces equal 

 to the subtrahend. 



The subtracting numbers of one digit, 

 the zero mark on the upper, or tens, wheel 

 raiust be set on the guide line, since the tens 

 place is not represented in the minuend. 



This machine is not difficult to make, 

 and it will be found very convenient by 

 anyone who does much figuring but not 

 enough to warrant the purchase of a 

 machine.— E. P. Thornton. 



7815 



A Simple Sawdust Deflector for a 

 Circular Saw Bench 



TO do away with the confusing spray 

 of dust which a circular saw throws 

 up, particularly when cutting heavy 

 lumber, a wheelwright made the ad- 

 justable sawdust deflector, shown in the 



rN/lEEOW STtElL TIEE 



5/qw T/qBLH 



The parts for making an overhanging 

 sawdust deflector for a circular saw table 



illustration, to cover his circular saw. A 

 length of narrow tire steel was bolted to 

 an overhead beam and bent so as to bring 

 it over to the saw as shown. This sup- 

 ports the vertical arm. A, of the deflecting 

 device. A short section of wood, B, was 

 bolted to the end of the tire steel, and to 

 this in turn, the vertical arm was secured 

 by a bolt, C, which permits the deflector 

 to be swung away from either side of the 

 saw table. 



The deflector proper, D, consisted of a 

 curved piece of wood 2} 2 or 3 in. wide and 

 about 1 in. thick, mortised to a 12-in. 

 vertical section of the same width. In 

 order to eliminate any chance of accident 

 due to cutting through of the deflector, a 

 wood pin instead of a bolt was used to se- 

 cure the mortise and tenon E. Vertical 

 slots in the ends of the arms F and G per- 

 mitted the travel of the wing-nut used 

 for raising and lowering the deflector. 

 Hanging a light on the deflector arm made 

 it possible to adjust both arm and light 

 in one operation. — James M. Kane. 



