“Nothing has a greater tendency to promote improvements in any branch of production than their trial under a new set of conditions.”

—John Stuart Mill.

Drills are undoubtedly the most popular and useful of all tools, and in a very crude form were used by primitive man in the Neolithic or Later Stone Age.

The exact date when the twist drill first came into use is not clear, and to attempt to state a definite date would be drawing a bow at a venture. The early lip or flat drill, which still has its uses, was the only available tool known to our ancestors.

This type of drill was a source of annoyance and dissatisfaction to engineers. It was very slow when used for drilling deep holes, and had to be repeatedly removed for the purpose of clearing the chips and cuttings. This lack of clearance engendered heat that drew the temper, and necessitated not only frequent regrinding, but also rehardening. A fast speed or a heavy feed meant certain disaster, consequently the rate of penetration was slow and tedious.

After much toil and experiment a crude type of twist drill was evolved. This was made by heating a length of flat steel and twisting it-not with the object of giving the cutting edge a workable rate, but to enable the chips and cuttings to find an easy exit when drilling deep holes and so obviate the necessity of continually removing the drill. Success was not to be so easily bought, however, and this type of drill (which resembles the present day twist bit used in wood working shops) did not come up to expectations. Practice refused to obey theory, and the chips and cuttings failed to find ready exit along the twists of the drill. Heat was again engendered, and the same vicious circle of break-downs, common to the flat drill, still remained the problem. Not to be defeated, a spiral grove drill was tried with a fair measure of success. The cork-screw like action of the spiral flute did convey the chips and cuttings from the point of the drill, thus minimising the disadvantages of the twist drill. But as speed was by no means a virtue of this type of drill the demand of the production engineer had yet to be met.

Something Attempted-Something done.

About 1880, Sir Joseph Whitworth and Mr. Greenwood designed a tool approximating in design the modern twist drill, and the Manhattan Firearms Company of U. S. A. promptly commenced to manufacture a similar tool.

Partial failure again loomed on the horizon it being found that the spiral flutes were much too fast, a fault which made the cutting edges over keen. Perserverance was ultimately rewarded when Mr. Morse, an American citizen, altered the lead of the spiral flutes and considerably reduced the cutting angles. The improvement brought the long-sought twist drill prominently into the commercial arena, and since then this tool, like the Village Black-smith, “can look the whole world in the face for it owes not any man.”

Very shortly after his first success, Morse devised the increasing twist and the grinding line (concerning the success of which there are two very distinct opinions). The champions of Morse claim that they greatly improve the drill's performance, whereas the upholders of the drill with the constant twist and no grinding line, respectfully beg to differ. Which is the better drill, however, can safely be left to the users to decide. Sufficient and gratifying is it to know that, like high speed steel, the incandescent electric lamp, the vertical boring mill, etc., this drilling demon was the outcome of Anglo-American inventive genius.

Prior to the advent of the modern high speed twist drill it took the best part of a ten-hour day to drill twenty one inch holes through a three inch mild steel plate. To-day the same work is performed in one hour, and with 25 per cent. less horse power. Engineers did not long hesitate in their repudiation of the flat drill, and in spite of the extra first cost, “an oft-time economic stumbling block,” the twist drill in a remarkably short time dominated in the drilling sphere of workshops activity.

The drilling out of cored holes presented yet another problem. Owing to the right handed action of the spiral, the two-fluted twist drill, by reason of its corkscrew motion being in advance of the feed, either pulled out of the socket and became jammed, or (if the machine operator failed to quickly stop his machine) the tang of the drill was twisted off or the drill broken. To overcome this problem page 35 a three or four-fluted drill was introduced. In design this tool is very similar to the ordinary twist drill, but has three or four cutting edges, and does not come to a point like the ordinary drill. This enables the web to be thickened up and it thus makes a much stronger and more serviceable tool for cored holes or the opening out of small holes.

Still looking ahead, the twist drill manufacturers are producing a drill capable of drilling tapered holes. This tool dispenses with the taper reamer except where a very high finish is required. On such work it is then only necessary to smooth and accurately size up the taper drilled hole. The saving of hard manual labour and the wear and tear on the taper reamer which at its best is not a friendly tool, will be only too readily appreciated by its friend-the fitter. (To be Continued.)