SCREWS AND SCREWING.
Page 29
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Useful Ideas Adopted with Success by Our Driver and Mechanic Readers.
THE apprentice to mechanical engineering gets into trouble most frequently because of taps which he breaks 'while he is putting a screw thread into a hole. He is doubly condemned for his carelessness, first, because of the cost of renewing a tap, and, Second, because of the trouble which is involved in removing that part of the broken tap whiCh remains in the hole. When this apprentice gets alder, and CAIlles to man's estate, he encounters trouble of that, kind but seldom, partly because he has learnt the knack of manipulating small taps in such a way that the risk of breakage is very small, and partly because the work of tapping holes is usually relegated to an apprentice. He does still, however, find trouble of a similar kind arising from the negligence of other people.
The popular method of removing a broken stud is to drill a hole down its centre, the diameter of the hole being somewhat less than that of the thread at its root. A. three-cornered file is then driven into the hale until its sharp and tapering edges have bitten into the metal of the stud. The projecting portion of the file is then held by moans of
gas tongs or other suitable instrument, and the piece of stud removed by turning the file so. as to unscrew the stud. There are at least two objections to this method. In the first place' the file is liable to break, and pieces of it fly in a dangerous manner while it is being hammered in, and, in the second, it may break inside the stud while the latter is being removed.
An interesting suggestion, embodying a more effective means of removing a piece of broken stud or setscrew, is conveyed in a-letter from "E.J.," of Sandbadh, to whom we award this week the prize of 15s. He-takes a piece of tool steel, of square section the dimensions being in accordance witli the size of the stud' which has to be removed. This piece of steel is ground to a gradual taper towards one end, until that end will just enter the hole in the stud. It is then driven in tightly, as shown in the accompanying sketch, and the stud removed by turning the teal by means
of a tap wrench or spanner. . • A ,eimilar idea comes from "HIT.," Of Highgate. He, however, uses round steel, ground to a taper of square section to one end, that which is made to enter the stud, and to a plain square at the other • end, to accommodate a tap wrench or spanner. This oorrespendent makes the further suggestion that pieces of broken or worn taps can be utilized for the purpose,and his sketch shows such a tap, with the dimensions to which it would have to be ground in
case it is required to remove studs of about in. diameter. As a general rule he states, it is convenient to -drill the hole in the stud about half its outside diameter; thus, in a On. stud drill a I-'in. hole, and in a I-in. stud a a-in. hole, and so ore
A rather more complicated and, toour mind, less practical suggestion comes from "H.A.B.," of Rotherham. He drills and taps a hole in the skid, the thread being a left-hand one. The removing tool is also screwed leftehand and tapers, as shown in the sketch. As it is screwed into the hole in the stud it simultaneously tightens itself in the hole in the stud and removes it. The expense of making such a tool would, we think, put it quite out of court, apart from the fact that few ordinary garages and repair 'shops have any egaipment of left-hantl-threaded taps.
A more interesting suggestion from he same correspondent tells how to rescrew studs which, by reason of the proximity nf other studs or projecting parts, may not be repaired by the use of ordinary stocks and dies, because the projecting handles of the stocks would encounter those studs or projections. Such cases arise whenever the studs on a crankcase or those for the covers of steam cylinders have been damaged and must be rethreaded, or, at least, have the threads trimmed.
Round dies being available in the particular instance which "H.A.E." has in mind, he procured a shed length of steel tubing (gas or steam piping wih serve the purpose equally well), having an internal diameter the same as that of the exterior of the die. At one end this tube must be drilled for a taming bar; at, the other several saw cuts should be made longitudinally, in order to facilitate engagement of the tube with the die.
A clip with wing-nut must be made next to fit "round -the outside of the tube and designed to squeeze the slit end of it on to the die, so as to grip it.
A different aspect of this screwing and studding problem is considered by " J.F.D.," of Broxbourne. He describes a simple tool for facilitating the replacement, or renewal of studs.
This correspondent suggests the use of a piece of hexagon bar, any convenient size across the flats and about 2 ins. long. This bar should be drilled centrally, as shown in the accompanying .sketch, for about half its length, the hole being subsequently tapped the same size and thread as the studs on which the tool is to be used. Take a piece of screwed rod, still the same size as the studs, and half an inch long. Dress one end perfectly flat, and put a saw cut in it to accommodate a screwdriver. Screw this well down into the hale in the bar, and the teal is ready for use.
Ffo use it, place a stud in the hole and screw it in "until it encounters the flat end of the small screw inside. Then insert the other end of the stud into the tapped hole where it should go, and drive it. in place by the use of a spanner -on the hexagon bar.
The important point in the making of this tool is to be sure that the: endeof the internal setscrewAis-quite fiat.