(a) ;If the plate to be cut is of thick section (say 1 in. and upwards), heat well down the edge before commencing to cut.

(b) ;Always be sure that the cut has penetrated right through the plate before commencing to advance the blowpipe.

(c) ;It is always preferable for the operator to draw the metal-cutter towards him.

(rf) It is of the utmost importance that the metal-cutter should be moved steadily and regularly at the best speed (see also page 427) in order to ensure good results. If through too rapid movement of the cutter the requisite heat should be lost, the valve G must be closed (by depressing thumb lever P) until the heat is recovered, when the valve can be again opened and the cutting recommenced.

(e) ;The tip of the white cone in the flame should be just clear of the plate when cutting.

(f) ;If a back-fire should occur through particles of metal impinging on the cutter nozzle, or through the operator allowing the nozzle of the cutter to touch the surface of the plate, the acetylene tap H should be closed for an instant in order to clear the passages of any mixed gas before relighting. If the back-fire has been serious enough to displace water in the hydraulic valve it must be refilled before restarting to cut.

(g) ;If the annular opening in the nozzle through which the mixed gases for heating are discharged should become partially choked by particles of metal or soot, the outer nozzle D should be removed and the parts cleaned.

(h) ;If the inner nozzle through which the oxygen for cutting is discharged should become choked (which is less likely to occur), and if the passage cannot be otherwise cleared, this inner nozzle may be removed and cleared by passing a copper wire through it. No reamer or sharp steel instrument should be used for clearing holes, as all passages are made the correct size and should not under any circumstances be enlarged.

(i) No other parts of the metal cutter are likely to get out of order, and the cutter should not be otherwise disconnected. Internal leakage will be indicated by constant back-firing and excessive heating of the shank of the cutter. External leakage at any joint can be usually stopped by tightening. Should leakage occur at the milled nuts of the " Universal " cutter, these can be screwed back and a fresh grummet inserted. (See also " Detachable Parts of Blowpipe," page 80.)

Cutting Under Difficult Conditions

(j) When cutting within a boiler or a confined space, care must be taken to see that there is ample ventilation by removing manhole covers, mud doors, etc., for it is essential to allow free egress for products of combustion.

(k) Only workmen physically sound should be allowed to undertake such work. They should have a mate in attendance upon them in charge of the cylinders of oxygen and acetylene generator, outside, ready to turn off the supply of gases at a moment's notice.

(l) A bucket of water should be available in a convenient position by the side of the operator for any emergency use.

(m) It is especially important that the joints between the rubber or metallic tubes and the blowpipe should be carefully examined from time to time to see that they are in order, and care should be taken to see that the tubes are free and not in contact with any heated portion of the work in hand.

(n) In cutting up the hull plates of ships or any other material with painted surface, the paint should be scraped away for a considerable width along the line of cut; otherwise the heat of the cutting flame which spreads inwards many cause injurious fumes to be given off.

(o) In cutting galvanised plates it is desirable for the operator to wear a gasman's respirator, which supplies pure air through a tube, as otherwise he is liable to inhale injurious zinc fumes given off through the heat generated in cutting.

(p) When piercing holes in a piece of plate the cutter nozzle will have to be held much farther away from the plate than for ordinary cutting. For plate above 3/4-in. thick it is not advisable to pierce holes by means of the cutting blowpipe, because there is considerable risk of molten metal being splashed about and up into the nozzles, causing the blowpipe to back-fire.

(q) It is an advantage to slightly tip the cutter and nozzle so that the inclination points in the direction of movement.

On very thick material the cut may be started at the bottom of the face to be cut, gradually working up this face with the blowpipe until the top is reached, when the cut may proceed in the normal manner.

(r) On thin material and constructional work the heating flame should be reduced as much as possible to prevent distortion and burning of the metal.

(s) It is an error to use a cutting oxygen pressure which is greatly in excess of those given in the tables, too high a pressure wastes oxygen and produces a wide cut.

(t) When cutting round bar, the side of the bar where the cut is to be started should be nicked with a round nosed chisel, producing a lip which will quickly attain incandescence.

(u) In cold climates and for material over 3-in. thick a regulator warmer should be employed. The heater prevents the regulator freezing and warms the oxygen in passing, reducing the cooling effect of the cutting jet as it impinges on the plate, and increasing the rate of cutting with a corresponding saving in oxygen consumption.

(v) In certain districts the water contains considerable quantities of lime and other impurities, producing scale on the inside of a boiler which should be removed by pounding or chipping before cutting is commenced. (British Oxygen Co., Ltd.)