Jury, 1944 AIRCRAFT ENGINEERIN G Workshop and Production Section By H. Moore TWIST drill should not always be regarded for a longer time. It must not be supposed, however, Drill cuttings, when the drill is cuttin g right, rise to as something fit only, for producing holes of tha t a minute variation from the standard is a th e surface in a regular spiral, or stream, according .serious defect, but certainly if the variation is to the material being drilled. The moment they approximate accuracy. With close attention considerable there is little hope of drilling a hole cease to appea r is th e tim e to withdraw the drill and t o the rules govering this kind of tool it is possible wit h th e quality of precision. clean out the flutes. A flat brush, or even a piece of t o turn out work with finished holes which are straight , smooth and to size: three most essential Although th e importance of th e cutting angle only felt, pressed against the drill a s i t is withdrawn, will conditions. In many cases, it is true, the work de ha s so far been emphasized there are two other effectually clean out the flutes of a drill. mand s the use of a reamer, but it is equally true that tilings of value; the central position of the drill Drilling a tape r hole with a drill is easier tha n one reamers are frequently used because th e possibilities . poin t and the backing-off angle. The same gauge would wish. Drills, of course, taper slightly back of drills have not been fully explored. A brief used for the cutting angle will show quite clea'rly wards , bu t if a drill ha s been used to cu t hard metal, description of some of this exploratory work can whethe r or not the point of th e drill is in the centre. or has been run at a speed too high for its size it refer only to the smaller sizes of drills; generally Th e backing-off operation is, however, more difficult; ma y be worn on the front end only. It is a good understood to mean all those below a quarte r of an in fact, no amoun t of reading can teach how to back habi t to measure all drills before using them to1 inch . Drills above this size are usually handled in a olf a drill—only an actual demonstration can do mak e sure they are not tapering the wrong way. manne r quite different from the others. that . Nevertheless, it is a fact that a drill ground to Grinding the end of the drill away until the worn a standard gauge is easier t o back off than one that par t is removed will make it serviceable again fori Before a drill of an y size can be used it mus t have is not. The procedure of th e full grinding operation some jobs, but it will be undersize and quite useless! a cutting edge ground at the end. This then, is the should be as follows:. for precision work. first tiling to which attention must be directed. Ignore the backing olf entirely and grind the If there is one momen t when the undivided atten Calculations, and experiments by expert mechanics, cuttin g edges flat, keeping the point of the drill tio n of the operator is required it is tha t moment have resulted in a standar d cutting angle of 118 deg. and, without any doubt, if this angle is closely centra l with reference to the gauge. When this whe n the drill is breaking through the work.. More adhered to a large par t of th e problem of good drill result is effected start backing off from the heel drills are broken, more holes spoiled and more acci ing is solved. Unfortunately, many operators think of the drill on each side and , with a rolling motion, dent s caused by inattentio n a t this tim e tha n a t any otherwise. They believe this angle to be of no graduall y work up to the cutting edges until other . It is not safe to say much on this subject particular importance and, as a consequence, the non e of the flat part remains. because th e condition s var y in eac h sho p and , indeed, sight of a correctly ground cutting angle on a small Th e care bestowed on the grinding of the drill wit h each job. It is often quite safe to drill into a drill is rather uncommon. This haphazard drill mus t be continued'on the drilling machine if results scra p piece of flat metal laid beneath the work, but, grinding is bad practice and ought to be condemned. of a precision characte r are t o be expected. I t should of course, much depends on the shape of the work. A gauge need not be expensive. In fact, a serviceable always be remembered that any undue shock or Th e machine stop also may lie used as a safety strai n will spoil the accuracy of a hole. What is device by setting it to stop the drill just before it one can be made of sheet metal ground out, or filed known in the shops as a "bent" hole is sometimes reache s the critical point. To finish the hole, the out, to fit a new drill, fresh from the makers. The th e result of a sudden jerk on th e drill handle forcing work is placed on a metal plate to raise it high thinner th e material is, th e bette r it will show u p any defect in th e grinding of even the smallest drill. th e drill over to one side. Once it has started going enough to allow th e drill t o be fed carefully through. off at a tangent a drill usually continues along the - Precision drilling, then, requires the use of good The defects arising from improperly ground drills sam e path unless it receives another bump heavy drills and good operators,' and it might be added, are often serious. If, for example, the angle is too enough either to force it back again or still farther good machines: Th e operato r is th e main contributor acute, it not only weakens the point, but also tends ou t of line. In the first case th e hole is bent, in the t o success, but even he, be he ever so skilful, is to make the drill wedge itself into the hole, and second, if th e hole is dee p enough th e drill is eventu unabl e t o produce a good job with bad tools. Drilling probably lead to an early fracture. On the other ally broken. To avoid suddenly jerking the drill a t one time was considered a rough operation, and hand, if the angle is too abrupt it leaves the point handl e the operator must not press with the whole drills were classed as roughing tools only. Drill strong enough but makes th e wandering tendency of weight of his arm, but rather with a movement of gauges were not the n in existence. To-day, however, th e drill difficult to control; and once a drill begins his wrist. This can be done only when the elbow is th e demands of industry are becoming more and t o wobble it continues to do so with a vigour which resting upon something, either the machine table, a more exacting. Work mus t not only be accurate , but increases with the depth of the hole. box, or even a block of wood upon the table. It is also finished with th e least possible delay. If a drill, The standard cutting angle contains none of these remarkabl e how much control this position gives, intelligently used, can be made to produce a hole faults. It is designed to secure maximum strength especially over minute drills running at high speeds. equal to a hole which has been drilled and reamed a t the point where th e drill is weakest . I t centres the Allowing the drill to become choked with cuttings the n one tool has been made to do the work of two, drill better and enables it to maintain its central is also the cause of defective holes. In this case the th e cost of the reamer has been saved, and both tlie position with less attention from the operator. cutting s ja m more tightl y in one tlut e tha n th e other tim e and energy of the worker used to the best Finally, it rolls th e chips off the cutting edges more an d force the drill over to the lesser jammed side. advantage . evenly and so helps t o keep th e drill clear of cuttings
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jul 1, 1944
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera