(5) Glass may be readily drilled by using a steel drill hardened, but not drawn at all, wet with spirits of turpentine. Run the drill fast and feed light. Grind the drill with a long point and plenty of clearance, and no difficulty will be experienced. The operation will be more speedy if the turpentine be saturated with camphor. With a hard tool thus lubricated glass can be drilled with small holes, say up to 3/16 in., about as rapidly as cast steel. A breast or row drill may be used, care being taken to hold the stock steady, so as not to break the drill.

(6) To file glass, take a 12 in. mill file, single cut, and wet it with the above solution - turpentine saturated with camphor - and the work can be shaped-as easily and almost as fast as if the material were brass.

Drilling Glass 500177Drilling glass.

Drilling glass.

(7) To turn in a lathe, put a file in the tool stock and .wet with turpentine and camphor as before. To square up glass tubes, put them on a hard wood mandrel, made by driving iron rod with centres through a block of cherry, chestnut, or soft maple, and use the fiat of a single cut file in the tool post, wet as before. Run slow. Large holes may be rapidly cut by a tube-shaped steel tool cut like a file on the angular surface, or with fine teeth, after the manner of a rose bit; great care being necessary, of course, to back up the glass fairly with lead plates or otherwise to prevent breakage from unequal pressure. This tool does not require an extremely fast motion. Lubricated as before, neat jobs of boring and fitting glass may be made by these simple means. The whole secret is in good high steel, worked low, tempered high, and wet with turpentine standing on camphor.

(8) The method usually recommended for boring a hole of considerable size in glass is by means of a copper tube fed with emery and turpentine. This may answer better in a vertical drilling machine than in the lathe, but amateurs who are not ordinarily happy enough to possess the former appliance, will usually employ the lathe, wherein it does not prove a very satisfactory process, being difficult to manage, horribly dirty, and exceedingly slow. The pressure necessary also causes a piece to be punched out with chipping of the edges of the hole at the back before the drill-tube goes clean through.

It is, of course, quite easy to drill small holes in glass by means of a properly hardened spear-pointed steel drill running at 100-200 revolutions per minute, and having to bore some 1 in. holes in discs of plate-glass 3 in. diameter, I thought it worth while to try what could be done with a steel tool. After several trials this finally assumed the form of a square-ended bar ground flat on one end, so as to have 4 working edges, and as a graver tool on the other, for clearing out the circumference of the hole as it progresses, and made very hard by getting, as the smiths say, "all the water."

A couple of the discs were fixed together with turners' cement, and fixed centrally on a wooden face-plate by the same means. When cold, the square* nosed tool, held at an angle of 45° to the horizontal, point downwards over the T-rest, had one of its edges pressed firmly against the revolving glass. The lathe was driven at about 60 per minute, and the work lubricated by just dipping the tool occasionally in turpentine. Too much turpentine flowing over the work does not answer. The action is not exactly a cutting one, but seems rather a kind of local breaking up of the glass immediately under the edge of the tool, which goes on evenly after the finest edge of the tool is lost, and is apparently the same as that which occurs in using the small drills for glass.

The hole, however, went merrily and cleanly through the outside plate without any considerable chipping at either surface. The graver point was used when necessary to keep the sides of the hole parallel. When, however, the outer plate was wedged off by the insertion of a knife blade, and the second proceeded with, some chipping occurred at the inside surface, since the wood backing did not give a sufficiently solid support. For this the remedy is easy and obvious. (J. Brown.)

(9) To make a small hole in a plate of glass is a comparatively simple matter. All that is required to do it is a very hard, sharp drill, some means for turning it, and a lubricant, such as turpentine, for causing the drill to cut rapidly. A drill made in the usual form from steel wire and hardened by heating it until it is dark red and then plunging it in mercury, will be very hard, but not tough. Before the drill is heated it should be driven into a block of lead, so that its point will just be enclosed by the lead, and after the drill has been hardened in the mercury its point should be inserted in the indentation in the lead, and the temper of the shank of the drill should be drawn over a lamp or gas flame to a blue. The lead prevents the drill point from becoming heated sufficiently to draw the temper, by conducting the heat away as fast as it arrives at the point. When the shank of the drill becomes blue to within a short distance of the lead, the drill, together with the lead, should be plunged into cool water.

The drill prepared in this way should be wet with turpentine while in use, to cause it to "take hold." It is advisable to drill from opposite sides of the glass whenever this is possible. The hole may be enlarged by means of a sharp round file wet with turpentine. When larger holes are required, these can not conveniently be made with a drill. A copper or brass tube charged with emery and water or emery and turpentine, and rotated in contact with the glass, will soon cut a hole a little larger than the tube.

Simple ways of guiding and revolving the tube are shown in Fig. 281. The glass to be drilled, which may be the plate of an electrical machine for example, is placed upon a table with a few thicknesses of paper underneath its centre. Two blocks are placed on the table at diametrically opposite edges of the disc and a thick bar of wood, which is bored at the centre to receive the copper or brass tube, is placed upon the blocks and clamped firmly to the table. The glass plate is arranged so that its axis coincides with that of the hole in the bar. The plate is then clamped in place by gently inserting two wooden wedges between the wooden bar and the glass.

The tube by which the cutting is done is stopped by a wooden plug at the middle of its length, and in the upper part is inserted a soft rubber stopper which rests upon the wooden plug, also a piece of heavy rubber tubing which rests upon the stopper. In the rubber tube is inserted one end of a close-fitting metal shank, the other end of which is fitted to an ordinary drill stock. This arrangement provides for a certain amount of flexibility in the connection between the tube and the drill stock. The tube is revolved by the gearing of the drill stock while it is supplied with a mixture of No. 4 emery end water or emery and turpentine. The pressure en the drill stock should be light, and the tube must be lifted frequently to allow a fresh supply of emery to 'reach the surface being cut. This device makes a hole in the glass in a short time.

If a larger aperture is desired, the glass is first drilled in the manner described, and enlarged by careful catting with a diamond. (Scient. Amer.)