and backwards, a distance equal to double the eccentricity of the crank arm. The throw of the crank should always be adjusted to give the saddle a traverse equal only to the length of the work to be cut.

It is easy to combine the plane-head and the traverse mechanism in one, but this is not so convenient as having them separate, because the traverse mechanism is useful for other purposes. For instance, with the traverse apparatus and a tool, such as Fig. 173, placed in the slide-rest, slotting or paring may be efficiently

FIG. 173.

accomplished on work fastened to the face-plate of the lathe. The circular motion of the lathe, and the straight line motion of the saddle-slide, allow a variety of useful work to be done which would otherwise require the laborious use of the chipping chisel and file. Amongst such work may be mentioned cutting keyways in the holes of wheels, and other articles, paring the curved parts of the bosses of levers that will not admit of being turned, shaping the edges of work that cannot conveniently be fastened to the slide-rest and planed.

The traverse mechanism is also useful in conjunction with the drilling frame for slot-drilling and other work.

ATTENTION TO THE LATHE, REPAIRING TOOLS, ETC.

Lathes and tools, being subjected to usage and wear, need care and attention to prevent unnecessary damage,

and occasional renovation to repair the deterioration resulting from ordinary wear.

The wearing surfaces of the slides should be kept lubricated with good clean oil, and dust or grit of any sort prevented getting about them. However much care be taken, it is not possible to keep off all dust; it is, therefore, advisable to occasionally take apart the wearing surfaces, and clean off all the oil and dust adhering to them, taking care to well lubricate the surfaces before again setting the apparatus to work.

Proper holes should be made to allow of easy application of the oil, and these holes should always be kept open and free from dirt, as otherwise they are worse than useless.

It is especially difficult to prevent grit getting between the surfaces of the slide-rest and bed; but this must be done as much as possible, or the surface will soon become scratched with deep lines, and also ' untrue.'

Soda-water does not rust wrought iron, but if allowed to remain on un-oiled cast iron for any length of time, rust will be formed; this, if not allowed to get very deep, may be rubbed off with a piece of oily waste, without leaving any disfiguration.

The various slides of the lathe and rest should be tightened up as soon as they wear slack and begin to vibrate, all well-made lathes having their slides provided with a loose cheek and side screws for the purpose of taking up the wear.

The necks of the lathe-spindle must also be screwed together whenever the spindle begins to vibrate, or give endways against the cut.

.

As a rule, all meddling with the adjustable parts of the lathe is to be avoided, and no change made unless required, which, with proper usage and good workmanship to begin with, will in every part be very seldom.

The lathe-centres must occasionally be looked to, and a spare set kept on hand. With use the stationary centre will get blunt, and they both, even with care, will sometimes get broken off; they will then need re-turning, and to that end must be first annealed, and then screwed into the lathe-spindle and turned to a gauge. The proper angle must always be retained. They must not, therefore, be turned at random, but turned carefully to fit a thin sheet steel gauge made to the right angle. They must then be hardened and tempered, after which placed again in the centre hole of the spindle, to see whether they run true.

It will sometimes happen that they were not screwed up quite tight when being turned, or that a bit of dirt. was between the surfaces that should have been in close contact, and sometimes the centre will warp in the hardening. In either of these cases, on the centre being returned to the lathe-spindle, and set in motion, it will be found that the points will not run true, but will be eccentric or erratic. An untrue centre in the lathe-spindle would cause the work turned on it to be eccentric to the centre mark, so that when changed end for end the turned part will run eccentric, and the shaft will be untrue.

An untrue centre in the screw-spindle may or may not make any difference; this depends on the position. of the point when in its place. If the point of the

untrue centre and the point of the proper centre be in a vertical line, the work will be either very slightly raised or lowered, and very little, if any, difference be made to it; but if that line be horizontal, the work turned between the centres will be either rather larger or rather smaller at that end than at the other.

Should a tool or drill break off, and become much damaged, it must be annealed, and brought to shape roughly again by forging or filing, after which it is hardened and tempered, and ground again to the right shape for use.

Most of the ordinary tools are hardened and tempered at one heating, the tool being made red-hot for some distance, and the cutting part only quenched in water, the heat in the remaining part being generally quite sufficient to reduce the steel until the proper coloured oxide is formed. When the end of the tool is quenched it is usual, on drawing it out of the water, to rub the hardened part quickly on a piece of brick, as this brightens it somewhat, and allows the colours to be better observed. When the required colour appears the whole tool is quenched in the cooling trough. Other more delicate tools are first hardened altogether, and then tempered by being held on a lump of hot iron until the colour appears, when they are again immediately immersed.

Circular cutters require that the water of the cooling trough should be still, and not oscillating or in waves; the hot cutters must also be immersed flatly and moved quickly but steadily up and down under the water.

6

They are best held by a three-branched spring made of wire, and passed through the hole; the wire does not interfere with the cooling, as it allows the water free access to the hole, which is a great desideratum, as otherwise the contraction is unequal, and the cutter frequently either warps out of truth or flies that is, cracks. These cutters require to be carefully tempered, but, so far as my experience goes, it makes no difference whether they are tempered by being placed on a hot lump of iron, or immersed in oil and 'blazed off.'

FIG. 174.

For heating tools and for light forging the neat little forge shown at Fig. 174, made by Messrs. Handyside, of Derby, is commended to the notice of amateurs.

Emery glazing-wheels, when worn smooth, are renovated by first washing off all the remaining emery, then coating with good glue, and rolling in emery of the required degree of fineWhen the glue is dry the

ness.

wheel is again ready for use.

The following remarks on tempering tools have been kindly contributed by Mr. James Nasmyth.

HARDENING AND TEMPERING STEEL TOOLS.

Whatever be the efficiency of the construction of a lathe or other machine for cutting metal and other materials, the excellence of the result must ultimately