ON SCRAPING AND FILING.
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Hints and Tips which will Interest Driver and Mechanic Readers of this Page.
S0-ME USEFUL hints and tips an scraping and filing are embodied in a letter from " A.E.," of-Mancheeter, tce whom we have this week awarded the 1s. prize. He tells us that the tools used for scraping metal parts are called scrapers. There are two general types. There are those which are used when the surface to be scraped is flat, and those which are necessary when that curface is rounded or hollow, either CORcave or convex. Scrapers for flat. sur faces are generally about one-eighth of in inch thick at the cutting edge, and are ground with that edge as nearly as possible square with the sides. Scrapers• for curved surfaces whether concave or convex, are usnally made from worn halfround files. It is most important to keep the cutting edges of all kinds of scrapers almost razor-like in their keenness, and for that purpose frequent. applicationof the oilstene is necessary.
The quality of is scraper is directly dependent on the steelof which it is made. A good steel will make a good scraper, and vice versa. Even the best of steels, however., may easily be spoilt by bad treatment in its handling when thetool is being made or sharpened. For this reason the greatest care -must be taken not to burn it.
The cutting edges ot scrapers must be kept, quite true, especially those which are to be used for scraping straight-surfaces. When grinding, use only a.grindstone which has a perfectly level-surface. When scraping. any part, be careful not to take too much off in any one place, as the result might be to reduc.e thow• places belew the general level, making it necessary egain.to scrape tha whole surface before a satisfactory job can be made of the work in hand.
When scraping the bearing brasses For a, shaft, commence by smearing the shaft journals with red-lead paste, put on very evenly and thinly. A suitable paste for this purpose is made by mixing red-lead
powder and lubricatin'g oil until the right consistency is obtained. Place the shaft in position in the: bearing and rotate a few: times. • Then -lift it, remove /Oho braSSes, and scrape those pasta which are • heavily marked with the lead. An even bearing should be; obtained over, the Whole of the. half-step up to within one sixth of the half-circle from the; butt
edges of the brass. Several trial., and scrapings will usually be necessary; depending upon the accuracy with which the, brass has been bored ih..the first place, and also upon the skill and experience of the -operator in the .second. A burnishing scraper is usually necessary to finish off important bearing brasses.
Scraping metal surfaces may appear, to the uninitiated, to be quite a simple operation. As a .matter of fact, the acquirement of the ability quickly to spot the high places, and to judge the amount which should be take off, involves much practice and expopience.
The accompanying sketch shows a, simple type of guide, by the aid of which the correct scraping of bearings may be considerably facilitated. The preliminary wood •block is made the same . diameter as the shaft for which the bearing is intended, and is somewhat longer than the bearingitself. It is sawn in two, as shown, and fitted with a pair of dogs, under which, when the guide is in use, the scraper is slipped. The method of use should. be apparent from
the sketch. .
Some Notes on Files..and Filing,.
As regards files, the following notes May be of use to the comparative beginner :--When filing something in a vice, the jaws of the vice. shriuld be at about the same height as the mechanic's elbow. Forty-two inches is a good height
at which to fix a vice which must be per manent. If the piece which is to be ,filed is small and deli-Wee r6quiving simply a reciprocating movement of the
arras of the mechanic, and a minimum
effort, then it would be better it the vice were -a little higher, so that the mechanic
may stand erect a-nd still have a close view of the work while he is operating upon it.. When the part is a heavy one. requiring a substantial menet of metal to be removed, then the vie should be a little lower, so that the man is above his work, he' approaches if. in a, slightly stooping posture, standing a little dis-tanee away, and thus can bring more of his weight to bear on it.
• The following -" Don'ts,! concerned with filing, are well worthy of note, even by some of the More experienced of the readers of this page.
. Don't use a small file when a larger One is really required. Don't use a fine file frn filing bearing metal, lead, or other soft material.
Don't waste time in the garage or worksbop• trying to file with a dull or worn file.
. Don't 'forget that it is r good plan to have a, rack iu front of your vice in which to keep all files. They may easily be injured if thrown, into a drawer, where 'they rub one upon the other.
Don't threw a file do-we heavily upon a instal or other hard surface, stir+ as a vice or a faceplate: such treatment is bound to injure the teeth of tite files,
Don't keep the files near spirits of salts, or other acids, 35 they Call9f5 the
files to rust. • Don't use the file as a hammer.
Don't throw old files away: they can be recut. by the sand-blast process at, considerably less cost than that entailed by the purchase of new files.
Etonit use a good file on tool steel: _a few strokes will ruin. it.
Don't use a. new, or bvess a moderately worn, file for removing the rust or scale from a casting always reserve an old file or two specially for that kind, of work. .
Don't neglect to make fret-pact-it use of the wire file card.
" J.S.S.,'' of Eccleshail, sends, is hint which they usefully be put in as an ap pendix to the first letter. He recommends, for the tiling of new Ford connecting-rod hearings, the use of a piece of broken craekshaft from the same
fairly well-known make of era'. Take care to select a piece of shaft which is perfectly round, and, saw-cut it as shown inthe sketch. Trim up the edges of the cut, removing all burrs. When preparing a new.set of big-ends, bolt on to the piece of shaft, and givea few turns in one direction only. The result, but for a lighttouch with a• scraper, is a perfectly fitting bearing.