(1) If for a cold set, have it very stiff; round the corners slightly. The principle in tempering cutting - tools for striking on, is to avoid the "hard line": the temper should die away gradually. The system adopted with success is as follows: - 1st. Always heat the tool a long way up. 2nd. Never dip in absolutely cold water. 3rd. Dip deep, and move the tool slightly up and down in the' water. Half - round tools :are most liable to fly; get it hot right up to head, and if there is not heat enough left to draw the temper in itself, get lump of white - hot iron to set the head on, or put head in fire.

(2) Quench in soft clay instead of water; it should be pretty stiff. Some things more susceptible to warping are done in this way. Plunge in sharp and straight.

(3) Get cutters just red - hot, and throw them into luke - warm water edgeways; they must be left in the water till all is cold, otherwise they will crack. If you cannot wait till the water gets cold, gently pour in cold water. If any warp, they can be put straight with a few blows over some hollow place when they are hot. In tempering them, do not trouble whether the teeth are sharp or round at bottom. By the above plan you will go over a large quantity in a very short time; only be sure not to take them from the water till all is cold.

(4) Make the cutter of as low a red heat as it will harden at, and quench (flatways) in water slightly warmed. In forming the teeth, make the bottom round, not sharp, as they are more liable to crack at those points.

(5) Take a bucketful of clean water, and add 1 gill of vitriol; stir up well, and bottle for use. This will last for years if kept corked up: when using it, put your cutter on the top of a piece of sheet iron, and when properly red drop into the liquor. This, when taken out, will be as hard as flint. Blaze, and let down to a purple for cast - steel. This has never failed in 1 case out of 50.

(6) Drive a lump of iron into the hole in the centre, and alter heating cutter and iron to the requisite redness for hardening, plunge both into the water. The heat in the iron keeps the steel round the hole hot sufficiently long to enable the steel to contract equally.

(7) "Carbonize" the fire by burning a lot of old scraps of leather, take a flat plate of iron, urge the bellows slowly to make this plate red - hot. Then lay upon the cutter, or saws, with another plate over this to throw the heat and carbon down until you can see it a pale red heat. Then take it off and slip it edgeways into about 1 qt. or more of oil. Do not use water. After being in about 1/2 minute take it out and place it between 2 pieces of very flat hard wood, and squeeze it very tight in a vice; it will now be ready for use.

(8) Very gradually heat over a clear coke fire to a dull cherry - red, and then slide it, as it were, into the water quickly at an angle of 10° or 15°. Use water with the chill just taken off.

(9) Adopt some method of preventing the water having access to the hole and to the central part of the cutter when quenching. A good way would be to provide a rod of iron, say 3/8 to 1/2 in. diameter, screwed (tapped) for a distance of 2 in, at the. end. First, put on a nut, then a broad washer, say 1 1/2 in., or even more, in diameter; next your soft cutter; then another broad washer, and lastly, a nut over that. Take plenty of time about heating the work, and have a good lot of fire ready blown - up; that is, avoid blowing the fire hot while the work is in it; but, on the contrary, have the fire already prepared, and let the work "soak," turning it over and over, till it is of an even temperature all over. If you prefer it, the piece of screwed rod need only be long enough to carry the work and the 2 nuts and washers, and you will then handle the whole with the tongs. Dip edgeways, and there will be no fear of flying in hardening. An incidental advantage is that it matters little if the cutter contracts in hardening, as sometimes is the case, for you can correct the hole by scraping or filing at your pleasure.

Always avoid leaving much substance towards the middle of your cutters; 1/16 to 1/8 in. thick in the central web, held between a flat shoulder on one side and a well - fitted washer and set - screw on the other, is sufficient for cutters up 'to 3 in. or 4 in. diameter for milling wrought - iron. If you leave them thick, they will go to pieces, unless you specially provide against the water reaching them. Use a charcoal fire if you can get one.

(10) For cutters 3 in. and upwards in diameter, the hardening process is a hazardous one, and causes some anxiety. In the first place, the lowest temperature at which the steel will harden should be ascertained. If at a blood - red heat, so much the better. The cutter, when roughed out to near the size before the finishing cut is taken off, should be well annealed. This precaution is too often neglected - whether for large taps, lathe mandrels, or cutters, it will be found, after the annealing, that a degree of warpage has taken place, showing that the steel, though soft, was nevertheless in a state of tension, and this preliminary annealing greatly lessens the tendency to crack in the hardening. For a cutter of 3 in. in diameter, a large clear fire of cinders should be used, great care being taken to heat the work uniformly. The cutter should be smeared over with a paste of soap and leather charcoal. This causes the finished cutting edges to come out bright and quite hard, after the quenching. Before hardening taps and drills, rub a piece of soap over them before heating, as no scale is then formed, and they come out clean after quenching.

For large cutters, etc, in order to lessen the risk of cracking during the quenching, pour oil over the water to the thickness of a card.