Sometimes it is necessary to heat, for the purpose of hardening or annealing, the tips of small tools, such as countersinks, etc. To do this without heating other portions of the tool is at times difficult to accomplish. If the tool is inserted into a raw potato, exposing only the part to be heated, the operation is easily performed.
South Portland, Me. J. V. N. Cheney.
To make an excellent hardening solution, mix pure rain water and salt strong enough to float a raw potato, and to twenty gallons of the brine add three pints of oil of vitriol. Tool steel may be hardened at a surprisingly low heat in this solution, a very great advantage, of course, when hardening difficult shapes. The solution, however, has one slight disadvantage in that it causes the steel to rust quickly unless the steel is thoroughly scrubbed in strong hot soda water immediately after hardening. Tools hardened in this solution should come out of the bath a beautiful silver gray color, and if there are any black' spots they are likely to be soft. I. W. Antano.
In hardening small tools, some of the more delicate and essential parts of the tool to be tempered are very apt to be overheated and burned unless extraordinary care is exercised. The following is descriptive of a compound that can be used to prevent over-heating of such small delicate Instruments during the process of tempering. Dissolve 2 ounces of pure castile soap in enough warm water to make a thin paste, and add to it the contents of a five-cent package of lamp black, mixing it well into a stiff paste. This must be kept securely sealed in a can. To use the compound, slightly warm the small tool or object that is to be hardened, and smear the paste all over it. When dry, heat and quench in the usual way. As the paste Is removed by the bath, the work will be clean enough to observe the color in tempering. T. E. O'Donnell.
To make a hardening solution for metal cutting tools mix saltpeter, 2 ounces; sal-amoniac, 2 ounces; alum, 2 ounces; salt, 1½ pound; and soft water, 3 gallons. Keep the solution in a stone jar, for it will eat a wooden tub and rust an iron pot. Do not draw the temper but only warm the tools enough to relieve the hardening strains. It is also well to rinse the tools well in water, for if this is not done the solution will rust them. Toolmaker.
The steel to be hardened should be immersed in a mixture of 4 parts of water, 2 parts of salt, and 1 part of flour. To get the steel thoroughly coated it should be slightly heated before dipping in the composition. After dipping, it is heated to a cherry red and plunged in soft water. This will make the steel harder than if simply heated and dipped in water. S. C.
Articles made of tool steel and polished may be hardened without raising a scale, thereby destroying the polish, by the following method: Prepare equal parts in bulk of common salt and fine cornmeal, well mixed. Dip the article to be hardened first into water, then into the mixture and place it carefully into the fire. When hot enough to melt the mixture, take from the fire and dip or roll in the salt and meal, replace in the fire and bring to the required heat for hardening. Watch the piece closely and if any part of it shows signs of getting "dry" sprinkle some of the mixture on it. The mixture, when exposed to heat, forms a flux over the surface of the steel which excludes the air and prevents oxidation, and when cooled in water or oil comes off easily, leaving the surface as smooth as before heating. Borax would possibly give the same result, but is sometimes difficult to remove when cold. E. C. Noble.
Rock Falls, Ill.