Page B1         November, 1935           NEWNES PRACTICAL  MECHANICS
0 cut a metal fitting out of a mild steel sheet of 2 mm. thickness might frighten some amateurs.
    Look at the illustration first of all, and cut a pattern in cardboard with the holes cut in it. Place this pattern on the steel sheet and mark it with a thick pencil or chalk. Fix the steel in a vice having jaws at least 4 in. long, and chisel it off with the edge of a cold chisel. Hold your chisel almost horizontally.
    If you are obliged to hold the piece which has to he cut, beyond the jaws, give the chisel it a slight slant in order not to tear the metal.
You will soon acquire the knack of holding the chisel at the correct angle for free cutting.
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One ought never to bend a piece of steel at a right angle, even for the smallest fitting owing to the hammering necessary which cracks the metal.
Always interpose between the piece you have to bend and the jaws of the vice a piece of steel of the same thickness which has already been correctly bent.
    Pierce the holes some distance from the edges. Where the drawings do not show the exact dimensions, always leave between the hole and the edge of the material a distance of 8 mm. to 10 mm. all round the hole.
    All bolts on an aeroplane ought to he made so that they cannot become loose. When it is a case of a piece which will often have to he taken down, fix the nut with a split pin or a safety pin. In very careful assemblages, use castellated nuts, or locknuts.
    When one does not foresee the necessity of frequently taking the pieces apart, it is quite easy simply to burr the end of the bolt with several blows of the hammer on the end of the bolt which extend 2 mm. beyond the nut. Before taking it apart, a few strokes with a file will replace the thread and remove the burr.
Every screw, axle, and wire bracing must must be securely fastened, because if you neglect to fix, voluntarily, a dozen screws, it may be that none will come loose ; but if you forget one only, and one which may be important, you can he quite certain that that one will come away.
    As you construct, or file, or screw, always think that one day the piece upon which you are working will hold you suspended in space several thousand metres above the ground.

The Main Landing Gear
    The axle is a tube 1.2 metres long in 36 mm. x 40 mm., reinforced internally witlh another tube 800 mm. long in 31 mm. x 35 mm. This makes a thickness of 40 mm., and weighs 4 kilos. It is very heavy, but it is solid and will not bend. You will not he afraid of damage when you are running over bumps. A single tube would not be sufficiently strong.
    The play of 1 mm. between the two tubes allows one to be pushed inside the other. If they were both the same size, you would not be able to got the inner one in place. A filling of hard wood is not suitable, because, although it is lighter, it only stops bending, but will not prevent breaking. Its elasticity allows the metal to fracture,and one day the axle will break under a light shock.