Access the full text.
Sign up today, get DeepDyve free for 14 days.
Workshop and Production Section AIRCRAFT ENGINEERIN G April, 1945 By H. Moore INC E th e design of drill jigs permits the adop particula r spindle. Anything, wood or shee t metal, word : try your own hand on them, not for a second, bu t for a full five minutes, an d see where it tion of an almost unlimited range of new ideas mad e to a channel iron shape will do a s well if th e hurt s th e most. it is curiou s t o not e th e lack of originality in th e real thing is no t available. It is possible, also, t o Th e smallest of all jig details is th e pin . Dealing minor components. Most of the common acces provide small shelves for th e bushings , attached to sories—clamps, screws, pins , bushings an d th e like — th e spindle heads just above the pinion shafts. only with th e locatin g variet y we find i t place d often hav e remained unaltered for years . And yet , in all This is bette r even than channel iron, bu t i t usually where i t i s mos t difficult to see . It migh t b e argued of them , there is som e room for improvement . It is costs more t o produce . A good typ e of spindl e shelf tha t th e shap e of th e wor k determines th e position tru e that the measur e of possible improvement is can be mad e of shee t metal, bu t in it s improvized of th e pin . But ofte n it is only too plai n tha t th e no t great; often it is merely a pin here, a screw form it is jus t th e lid of a tin held t o th e castin g b y a moving of th e wor k around would re-position th e there, an alteration of a n existing part, or perhaps small screw. After all, it is th e position of th e shelf pins in a bette r way. Not nearl y enough thought is only a rearrangemen t of some of th e parts . But all tha t is important , not it s materia l or shape . given to thi s aspect of jig work . The troubl e ap thes e changes are withi n the scope of th e operator pear s t o lie in th e inabilit y of th e ji g make r t o mul Turnin g now for a moment to screws. It is a himself; he shoul d not wait for th e jig produce r t o tiply b y thousands . It might b e eas y t o place on e matte r for surpris e tha t th e slotte d variety continues furnish him with ideas. As a matte r of fact, if an y to b e used on jig wor k when there ar e so man y really piece in a jig i n a good light—and most tool rooms ar e better lighted than th e shops—bu t t o repea t th e little defect is allowed to continue unchecked it is good types of safety screws on th e market . The performance a thousand times in a poorer light is th e fault, no t of th e producer , bu t of th e ji g operator slotted screw is th e sourc e of on e of th e few dangers somethin g entirely different. It is sometimes pos who, because h e is using th e jig in actua l practice, of jig operation. The real danger, of course, lies in is in th e bette r position to see wher e it is wrong. sible, however, to obtain a slight alleviation by th e screw driver which so often slips off th e screw At any rate, as far a s th e presen t writer can ascer drilling a hole in th e wall of th e ji g t o ligh t u p th e and lacerates th e han d of th e perso n holding th e jig. tain , nothing on thi s subject has ever before been obscure pin . Wheneve r these screws are i n a jig, and canno t for published from th e ji g producin g end. It remains, any reason be changed , they should be rendere d as Althoug h cutting tools ar e no t strictl y speaking jig therefore, for someone at th e other end—the jig harmless as possible. Grinding a portion off th e details they cannot entirely be excluded from th e operatin g end—to point out som e of th e defect s of end until th e head is well below th e surface reduces argument . There are a few ne w thing s to b e said. small accessories an d ho w t o correct them. These th e danger. Deepening the slot to twice or three Counterbores and facing tools, for example , usually notes, althoug h the y chiefly concern th e operator , ar e time s its norma l depth and grinding th e screwdriver carr y a collar or lock-nuts as stops. The overall directed to th e produce r as well, because many of to fit actuall y t o th e botto m is also a good safeguard. dimension t o whic h these mus t be se t is stampe d on th e ideas t o b e mentione d could well b e incorporated An additional precaution is the rounding off a pad in th e ji g nea r th e hol e in which the y are used. in th e ji g before it is delivere d to th e shop . smoothl y of all th e shar p edges on th e screwdriver This dimension is always given in decimal figures, blade. There will b e muc h less danger of it s cutting which are liabl e to accidental alteration. A slight Th e loose bus h tha t fits into th e liner bush in th e the n and a screwdriver with rounded edges fits into knock in th e righ t place and th e figure one becomes jig body is a n excellent example of a component a screw slot more readily than without. a seven, a nought becomes a nine an d so on . Any which never alters bu t which is, nevertheless , cap one experiencing trouble from this cause should mill abl e of minor improvements. For instance, it is Ho w th e usefulness of a component may b e in difficult to understand why drill and reame r loose th e figures off an d replace the m with letters. When creased b y a simple alteration of a n existin g par t is bushes are alway s made with only th e letterin g on 1.315 becomes "one point three one five" there is bes t illustrated by th e sprin g lifted slotted clamp. th e top t o identify them; when a groove in th e little chance of erro r from accidental cause. This clamp is used th e world over. It is a flat piece middle of th e reame r bushing head would reveal it s Th e setting of tape r reamers is alway s a delicate of steel with a long slot in th e middl e through which description at a glance. An error of really long jo b when the machine stop is used. Fortunately, th e tightening bolt passes an d underneat h which, on standin g concerns the loose bush that projects a ther e is usually some par t of th e ji g wher e it is pos th e bolt, is a spiral spring. Now th e function of thi s considerable distance inside th e jig . It is because spring from time immemorial has been solely to sible t o mak e a tes t hole—mostly in th e feet. With this projecting par t is no t left small tha t th e operato r lift the clamp clear of th e work when the, bolt is a taper hole th e correct depth in th e ji g itself there is compelled to exhaus t himself twisting tight bush loosened. But th e operator has still t o pull th e is no difficulty in setting the reame r either to th e ings all th e wa y dow n and out . Small bushings ar e clamp back t o th e en d of th e slo t before he ca n re machine stop or t o a collar on th e reamer itself. th e cause of muc h needless exertion. It is a mistake move th e work—an d often there are a dozen of thes e Many operators find it har d to se t a countersin k in a t o mak e th e head s of smal l bushings proportionately clamps on one jig. Yet, i t require s only a small hole jig. The simplest and sures t way is t o us e a steel small merely because they look nice. They should in the jig near the bolt and a similar one in th e block with th e requisite countersinks in i t th e same be large—even to th e point of ugliness—and the underside of th e clamp , into which th e end s of th e height from the tabl e as thos e in th e wor k when it knurling made a s roughl y as possible to enable th e spiral spring, after giving it a twist, are inserted; is in th e jig . The block, of course, is kep t always operato r to ge t a good grip. in th e sam e box a s th e jig . The reamin g of blind an d th e sam e spring not only lifts th e work , bu t also holes in cas t iron calls for mentio n here because it is I t is, however, in th e dispositio n and th e handling pulls it back out of th e way . It should be pointe d one of th e job s tha t causes difficulties far ou t of pro of loose bushings tha t most of th e scope for improve ou t here that a spring tha t fits th e bolt too closely canno t be used for thi s dual purpose. portion to their apparent simplicity. The troubl e men t lies. Some jigs have two dozen or mor e an d is tha t the reamin g cannot be done until the drill much of th e cost of productio n will depend on how Nex t to th e slotted clamp, probably the best cutting s have been removed from the hole. This is thes e are handled . The ide a behind all loose bush known of all clampin g devices is th e ji g leaf. The effected on small jigs b y turnin g them over t o allow ing arrangements is, of course, to provid e a known screw used for tightenin g this has a flat head equal th e cuttings to fall out. But quit e a jarring effect place for each of the m and so t o ensur e tha t th e on e in width to th e slot in the leaf. By giving it a is needed in addition . For thi s reason it i s bette r t o needed shall be th e one alway s nearest to hand. quarte r tur n back th e slot i n th e leaf will pas s over it ; If th e bushings ar e few an d on e only used with each drill all th e holes first. This necessitates' turning a quarter turn forward and i t will be locked. The tool a mix-u p can b e avoide d by leaving th e bushing th e jig over to reach the various holes and this screw is moved with a spanner and it is almost on its respective tool in the revolving spindle. movement, together with the vibration caused b y impossible t o sto p th e loosening movement with th e Slightly knurling th e shan k of th e drill or reamer th e drilling, effectually clears th e cutting s from all screw head exactly in line with the slot. Usually th e holes. will enlarge it enough to preven t th e bushing s from it goes past and ha s t o b e turne d back. To force falling off. Sometimes th e shap e of th e jig permit s th e head to stop in th e righ t place it is necessary Ther e is much more to be said but within th e th e drilling of a rough hole, a t each side of th e real only to pu t a pin in th e leaf close t o th e slot . Thus limits of a shor t article i t is possibl e t o mentio n none hole, into which the bushings can b e placed each simply can a n annoyance be ended—yet one ma y bu t the best known and most used components. tim e after use. Naturally, the difficulty of th e look a long time before one sees a stop pin in a ji g And even thes e mus t b e touche d on bu t lightly . The orderly arrangement of bushings increases with th e leaf. Before leaving this jig ther e is a detai l a t th e essential purpose, however, is t o point out tha t a numbe r used with th e jig. It makes n o difference othe r end tha t should receive some mention. It is proper attention to detail s is no t only desirable bu t how carefully these are arranged on th e dril l table ; th e handle designed to resis t th e torqu e of th e drill. imperativ e if th e fullest possible advantage is t o b e the y are alway s liable t o b e swep t off wit h th e cut Sometimes it bear s a slight resemblance t o a handle, gained from their use. The perfect drill jig is th e tings or displaced by th e movemen t of th e jig . A often it is jus t a straight , flat piece of metal . It is a one that can b e operate d with the leas t amount of length of channe l iron—two inch will do—laid across mistak e t o thin k tha t th e shap e of thi s handle is no t effort and th e fewest number of movements. The th e table a t th e bac k will provide a n excellen t place important . Anyone who has held one for an y adoption of any of the ideas which have been for the bushings used on a six spindle drilling lengt h of tim e against th e torqu e of a dragging drill- described here will contribute helpfully towards machine. In this is laid, behind each of th e will agree tha t few thing s can b e mor e tiring. To makin g jig wor k easier and mor e profitable than it spindles, th e bushings used with the tool in that all those engaged in th e manufactur e of ji g handle s a ha s ever been before. "Euco" Giant Blue Print Wall Chart of Free Trade Catalogues Wanted Trade Publications Received man's Screw Thread and Engineering Tables. Magneto Testing Equipment Any firms interested and associated in th e pro [Euc o Tool s Ltd. , London . 10s. 6d. ] Engine Starter Test Equipment duction of machin e tools, factory plant and equip ment , physical and chemical laboratory equipment, [Cit y Electrical Co., London. ] "Compo" Oil Retaining Bearings electrical equipment, switch gear, motors, trans 'Sieray' "Warm White" Fluorescent Lamps, "Bound Brook" Graphited Bronze Bearings . formers, generators, etc., hydraulic pumps, air [Siemens Electric Lamps and Supplies Ltd. , compressors, etc. , wh o ar e willing t o deposi t a copy London.] "Ferrocile" (Powder Metallurgy) Iron Valve of their latest catalogues are asked t o sen d the m t o Scrivener Centreless Grinding Machine No. 2 . Guides th e Librarian, Power Jets (Research and Develop [Arthu r Scrivener Ltd., Birmingham.] [Boun d Brook Bearings (G.B.) Ltd., Bir - ment ) Ltd., Whetstone , Leicester, for inclusion in Bakelite Resins mingham. ] th e trade catalogue section of thei r Library. [Bakelite Ltd., London.] 12 2
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Apr 1, 1945
Access the full text.
Sign up today, get DeepDyve free for 14 days.