Page:Popular Science Monthly Volume 88.djvu/801

 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.

�� �