Show ACTION OF ELECTRIC AIR DRILL FRANK RICHARDS INE IN E M JOURNAL the practical information in the journal of sept 22 concerning the cost of operating the electric air drill seems to invite discussion of other features of it the drill being new and as yet not fully known and nd understood it may be considered proper to offer a little sketch of its construction and operation the drill is not at all an electric drill according to the idea which the term usually conveys but has an air operated piston and so far as the striking of the blow is concerned it is as completely air operated as any drill ever built there is a drill cylinder sliding in a shell with a feed screw the shell mounted upon a tripod bar or column in the usual way the normal pressure of these bodies of air being about thirty pounds gage the pressure is alternately much greater and then much less than this for each rotation of the crank shaft and each corresponding stroke of the drill this arrangement instead of being a complication is in fact a great simplification of the usual air operating arrangements all of the parts of the drill which usually give trouble and cost so much for repairs or renewals are eliminated and the compressors which in this case may more properly be called pulsations have no valves and no water jackets there is no heating up in operation as the heating and the cooling effects of compression and mina t J 7 7 A aar aa 05 4 z e t t 4 view of electric air drill there are however no valves or valve operating devices no buffers or yielding connections for the heads provision is made for rotating the drill piston and that is all the mechanism about the drill proper practically as near the drill as possible is a little truck upon which is mounted a small electric motor which is geared to a shaft carrying two cranks that alternately operate the two single acting trunk pistons of two vertical air compressor cylinders A short length of hose connects one of these cylinders with one end of the drill cylinder and the other end of the drill cylinder is connected by another hose to the other air cylinder there are thus two distinct bodies of air which play back and forth without in any way communicating with each other and by the alternating pulsations of these two bodies of air the piston is thrown back and forth re expansion balance each other the apparatus thus briefly described comprises everything beyond the generator and wiring it has happened to more than one of the great mechanical inventions which have made their mark upon our industrial progress and have found permanent and growing employment that the original inventors of them were far from realizing some of their most important and valuable properties and possibilities I 1 wonder how completely the inventor of the electric air drill knew his invention just before the first trial of it the completeness of the invention in detail at the very beginning would indicate that the inventor knew with equal completeness what lie he was about and yet was it not more or less a surprise to him and of course a very welcome one that the drill would strike so hard a blow if he was not so surprised many other have been and many more will be As an experienced runner and tester told me she strikes the wickedest wick edest blow yet it strikes such a blow that they tell me it is generally advisable to dress the bits a little blunter than usual so that they will be less apt to break after the fact of the wicked blow is realized it is not really hard to find the explanation of it although few would have studied it out in advance in the standard air driven drill the piston when working is running away from the air that is driving it the working air pressure in the pipes is practically constant or changes very slowly and the throttle and the ports will let the air in only at a certain velocity at the best so that while the speed of the piston is increasing the pressure behind it will not fully keep up with it and the piston in each separate stroke is thus driven by a constantly diminishing pressure in the cylinder from the start at the same time the air on the other side of the piston which has to get out of the way has only a restricted passage and a constant pressure that of the atmosphere beyond it so that with an accelerating piston movement the pressure or resistance in front of it must necessarily increase as the th e piston advances and goes taster faster I 1 am not saying here how much the piston driving pressure will thus decrease during the working stroke or how much the opposing or exhaust pressure will wi 11 have increased increase at the precise moment when the rock is struck but the fact of such simultaneous decrease and increase of pressure seems to be indisputable now in the electric air drill the compressor piston is pushing in the drill piston the body of air in the hose and in the connected ends of the cylinders communicating or delivering the push the drill piston starts with a big pressure behind it due to the compression of the air in the cushioning of the return stroke and then the compressor piston being crank driven follows up this pressure with a rapidly accelerated advance so that the drill piston up to and somewhat beyond the middle of the stroke of the compressor piston is followed and driven not by a decreasing but by an increasing pressure and this pressure when at its highest is practically maintained upon the drill piston until the rock is struck in operating the drill it is evident that the precise point of the drill piston stroke at which the rock is struck is a matter of considerable importance and we can assume that more judgment may be required in feeding the electric air drill than the standard air drill but this judgment will soon develop in the runner and the drill itself will show a disposition to insist upon its rights as to its proper feed this crank acceleration of the compressor piston thus causing an increasing pressure behind the drill piston necessarily im plies also a diminishing pressure in front of the piston both conditions operating cooperating co to produce a more rapid acceleration of the movement of the drill piston and a consequently higher velocity when the rock is struck thus accounting for the wickedness of the blow it is to be remembered that the pressures in this apparatus are at no time absolutely high as the cylinder diameters are large so that the differences feren ces ot of pressures which occur and the of the differences either way count for more than in the old style drill another decidedly valuable property of this drill may have been thought of by the inventor in the beginning and later perhaps also by others when they have come to study the working of it but a great many will not have thought it out in advance and that is the habit which the elect electric rid air drill has of yanking itself tree when the bit sticks in the hole and going right on with its work again if I 1 were a drill runner which I 1 never was and never will be the most trying thing to me would be the sticking of the bit in the hole with the old style of drill when the bit sticks and the dead pressure of the air is not enough to pull it free at once that ends it as far as the drill is concerned and time begins to be lost on the job from that moment the steel has to be hammered and the feed has to be run up or down and a lot of coaxing has to be gone through with before the drill settles down to business again the electric air drill never gives up like that it if it is running along at the rate of or blows a minute and the bit sticks the motor and the compressor take no notice of the interruption but keep going right along at the same speed as before this means or jerks a minute on the steel in both directions and it would be impossible for anybody to think of anything more effective for freeing the bit than just that generally before a wrench can be grabbed to hit the steel the drill is running all right again the drill thus saves a lot of time for itself by not wasting it as the other does where there is no actual dead stop of the drill in the hole but just dragging or sluggish action on account of choking or muddling the pull of the electric air drill gets along with the trouble better than the old drill because the pull is stronger the above is of course more or less speculative in character and must not be taken as coming from one who knows everything for certain it shows my willingness to try to provoke others to think up and to talk about the working of this very novel and highly interesting drill if my explanation of things is not more or less correct as far as it goes will not someone help to set me right upon it there are certainly many things to find accurate statements of and adequate accountings for in connection with the practical working of the electric air drill |