Popular Science Monthly 



773 



Inside Counter-Boring in a Miller 



THE problem of securing the counter- 

 bore shown in Fig. /, may be solved 

 by means of a cutter C, shown in Fig. //, 

 This cutter is made for left and right, 

 for use in a milling machine running only 

 in one direction. It is a snug fit on the 

 shank D, one end of which is held in 

 the chuck, as shown in Fig. ///. The 

 small diameter of the shank is a few 

 thousandths of an inch smaller than the 

 hole, which is drilled through the sides 

 of the work, shown at A, Fig. /. 



The method of holding the work is 

 shown in Fig. ///. After being placed in 

 the vise, it is lined up with the end of 

 the shank, which is held in the chuck. 

 The cutter is then placed between the 

 sides and the table moved inward. 

 This runs the cutter on to the shank to 

 which it is fastened by means of the 

 screw E. — C. Anderson. 



r/G.i 



f/G.T. 



A solution to the problem of getting the 

 counter-bore shown in Fig. I 



How to Improve a Pocket Spectroscope 



SMALL direct-vision spectroscopes 

 are very popular with many amateur 

 experimenters and are comparatively 

 inexpensive. The utility of an instru- 

 ment of this type can be greatly increased 

 by a few simple improv^ements which 

 can be made by anyone who is handy 

 with tools. 



The most important addition is that 

 of a comparison prism, whereby light 

 from two sources can be viewed simul- 



taneously and the spectra compared. 

 This is shown in Fig. /. A small right- 

 angled prism P, with >^-inch sides, is 

 fixed at the slit end of the spectroscope 



y___ 



LEAO 



A comparison prism can be added to a 

 pocket spectroscope with little difficulty 



S, the position being carefully adjusted 

 so that exactly one-half of the narrow 

 slit is obscured, as shown in Fig. //. 

 Strong isinglass cement, or an alcoholic 

 solution of shellac, may be used as an 

 adhesive and will be entirely satisfactory, 

 if the instrument is carefully handled. 

 Light proceeding from a source A' 

 immediately in front of the spectroscope, 

 will pass directly through the uncovered 

 half of the slit; while light coming from 

 the side, as at F, and entering the prism, 

 will be refracted at right angles to its 

 former direction and made to pass 

 through the covered half of the slit. In 

 this way two spectra can be seen, one 

 above the other, and compared. 



It is a great convenience to fasten the 

 spectroscope to a stand, thus leaving 

 both hands free. A simple stand that 

 can be constructed without difficulty, 

 is shown in Fig. ///. The spectroscope 

 S is gripped between two wooden blocks 

 B and C, hollowed out at one end. A 

 gentle grip is all that is needed. This 

 can be secured by the use of a small 

 brass bolt A, passing loosely through 

 large holes in both blocks. The lower 

 block B is perforated at the end to slide 

 up and down a rod D, fixed upright in 

 the center of a wooden base. A thum- 

 screw E, serves to hold the block at any 

 desired height. To make the stand 

 steady, the base should be weighted 

 with lead. — H. J. Gray. 



