Blacksmithing Secrets Part 1
Forging, Tempering, and Welding
The material in this article originally appeared in ‘Shopwork on the Farm’, a textbook by Mack M. Jones, copyright 1945, McGraw-Hill.
With each new wave of uncertainty, and with each new out-migration to the countryside, there is renewed thirst for information on basic crafts and skills, information which may help to grant the individual and the family an increased measure of self-sufficiency. Blacksmithing, that ages old art of heating and shaping and welding metals, slips in and out of favor as a craft to learn. Today, in our time of wire-feed arc welders and fancy tools, there are many who see this skill as completely obsolete. And then there are the rest of us who take infinite pleasure and comfort in being able to start a fire in our forge, heat a piece of steel, and shape it by hammer blows.There are those of us who know that this craft will always have practitioners who treasure the Blacksmith’s Secrets. LRM
Whether a farmer can afford a forge and anvil will depend upon the distance to a blacksmith shop, the amount of forging and other smithing work he needs to have done, and his ability as a mechanic. Although not every farmer can profitably own blacksmithing equipment, many farmers can. If a farmer cannot, he should remember that a great variety of repairs can be made with the use of only a few simple cold-metal working tools.
Although blacksmithing is generally more difficult than woodwork, most farm boys with average mechanical ability can soon learn to do simple blacksmithing and will feel well repaid for their efforts. In all mechanical work, much more rapid and satisfactory progress can be made by a study of theory and principles along with practice. This is particularly true of blacksmithing.
Selecting Forging Equipment for the Shop
The Forge. The forge for the farm shop should have a gear-driven blower operated by a crank, and it should have a hearth at least 18 in. wide, preferably somewhat larger. A good way of providing a good forge is to get a good blower and make a hearth or stand of concrete or brick, or of pipe or angle iron. A plate with holes drilled in it can be mounted in the bottom of the hearth for admitting the air blast. The forge should have a hood and smoke pipe for taking away the smoke.
The Anvil. Anvils are of two general kinds: cast iron and steel. Steel anvils are much better and should be used if they can be afforded. The two kinds can be readily distinguished by striking with a hammer. A cast anvil has a dead sound, while a steel one has a clear ring.
Anvils are commonly available in sizes ranging from 50 to 200 lb. An anvil weighing 100 or 125 lb. is quite satisfactory for the farm shop.
A piece of railroad iron or rail 24 to 30 in. long and mounted on a block or stand makes a good anvil for light hammering and riveting, although a much greater variety of work can be done on a regular anvil.
Place the anvil on a substantial mounting, preferably of wood. Locate it in front of the forge, so that the workman can take irons from the fire and place them on the anvil by simply making a short turn and without the necessity of taking even a full step. Place the horn of the anvil to the left for a right-handed workman and to the right for a left-handed man. Mount the anvil at such a height that the top can be just touched with the knuckles of the clenched fist when standing erect and swinging the arm straight down (see Fig. 427).
Tongs. A few pairs of tongs of different sizes and kinds should be provided for the farm shop. Various types are available, the most common ones being flat-jawed tongs and hollow-bit curved-lip tongs (see Fig. 428). The hollow-bit curved-lip bolt tongs are probably best for general work. They can hold flat bars as well as round rods and bolts, and the curved part back of the tip makes it possible to reshape them easily to fit various sizes of stock. By filing or grinding a groove crosswise in the end of each lip, they can be made to hold links and rings practically as well as special link tongs. Tongs 18 to 20 in. long are a good size for average work.
Hammers. A blacksmith’s hand hammer weighing 1 1/2 or 2 lb. And another weighing 3 or 3 1/2 lb. will handle all ordinary work very satisfactorily.
Hardy, Chisels, Punches. There should be at least one hardy of a size to fit the hole in the anvil, and it may be advisable to have two, one that is thin and keen for cutting hot metal, and one that is thick, heavy, and tempered for cutting cold metal. It is a good plan to have a fair assortment of various sizes of chisels and punches. These can be made easily in the shop. If considerable blacksmithing is to be done, it would be well to have a hot cutter and a cold cutter (simply large chisels with handles on them) for heavy cutting with a sledge hammer. It would be well also to have one or two large punches with handles on them for punching holes in hot metal. Punches for making holes 3/8 in. and 1/2 in. in diameter are probably most useful.
Vise. One vise can well serve for all metalwork in the farm shop, including blacksmithing if it is heavy and strong. A blacksmith’s steel leg vise with jaws 4 to 5 in. wide is generally preferred as an all-purpose metalworking vise. A leg vise is one that has one leg extending down to be anchored or fastened into the floor (see Fig. 429). Such a vise can be used for heavy hammering and bending better than other types. If there is a strong steel mechanist’s vise in the shop, it can be used for blacksmithing work if care is used not to do too heavy hammering or bending with it.
Fire Tools. A small shovel and poker or rake will be needed for use on the forge fire. These can easily be made in the shop. A flat piece of heavy sheet iron about 3 or 4 in. wide by 4 or 5 in. long, riveted to a bar or rod for a handle, makes a good shovel (see Fig. 430A). A 1/2-in. round rod, with an oblong eye in one end to serve as a handle and the other end flattened and curved, makes a good combination poker and rake (see Fig. 430B).
Measuring Tools. Some kind of metal rule will be needed for measuring and checking pieces being forged. A small steel square is very good for both measuring lengths and checking angles and bends. A caliper rule (see Fig. 431B) for measuring the diameter of rods and thickness of parts, although not a necessity, will be found convenient.
Building and Maintaining a Forge Fire
A good fire is the first requirement for good blacksmithing. Many beginners do poor work simply because they do not know the importance of a good fire. Two students sometimes attempt to use the same fire. This is usually a waste of time as it is difficult or impossible to heat irons properly when someone else is poking in the fire and trying to heat other pieces at the same time.
A good fire has three characteristics. It is clean, that is, free from clinkers, cinders, etc. It is deep, with a big, deep center of live burning coke. And it is compact, being well-banked with dampened coal.
Starting the Fire. To start a fire, first clean the fire bowl with the hands, pushing all coal and coke back on the hearth and throwing out all clinkers. Clinkers are heavy and metallic and have sharp hard corners or projections and are easily distinguished from coke. Coke is light in weight and is easily crumbled in the hands. After removing the clinkers, shake the fine cinders and ashes through the grate into the ashpit below the tuyere (that part in the bottom of the hearth through which the blast comes). Then dump the ashpit and try the blower, making sure that a good strong blast comes through. Sometimes ashes work back into the blower pipe and obstruct the blast.
After the fire bowl is cleaned, light a handful of shavings or kindling from the bottom and drop them onto the tuyere. Turn the blower gently and rake fuel, preferably coke left from the previous fire, onto the burning kindling. Once the fire is burning well, rake on more coke, and pack dampened coal on both sides and on the back of the fire. This forms a mound of burning coke at the center. The dampened coal on the outside concentrates the heat in the center. In a little while gases will be driven off this dampened coal, sometimes called green coal, and it will change to coke.
If the fire tends to smoke excessively, stick the poker down through the center, opening up a hole and allowing the air to come through more freely. Most of the smoke will then usually catch fire and burn.
Always use blacksmithing coal in the forge. It is a high-quality soft coal that is practically free from sulphur, phosphorus, and other objectionable impurities. When dampened and packed around the fire, it readily cakes and changes to coke, which burns with a clean, intense flame. Ordinary stove or furnace coal will not work satisfactorily in a forge.
Keeping the Fire in Good Condition. When the coke at the center of the fire burns up, replace it with more coke. This may be done by mashing the fire down in the center with the shovel or rake, or by raking coke in from around the edges of the hearth, or both. Always keep the fire deep. Do not let it become hollowed out and shallow.
Add green coal to the outer parts of the center mound from time to time, as may be required to keep the fire well banked and confined to the center.
Do not continually poke at the fire; simply keep the center well supplied with coke and the outside packed down with dampened coal.
If the fire tends to spread too much, or if it becomes open and loose, throw or sprinkle water on the outer edges and pack it down with the shovel. Use only a moderate blast of air. Excessive air makes for slow heating and scaling of the irons. If a moderate speed of the blower fails to produce enough air, check for leaks in the pipe between the blower and the tuyere, or for a partial stoppage with ashes.
Cleaning the Fire. From time to time — usually every half hour when welding — remove the clinkers and cinders that accumulate over the tuyere. To do this, simply pass the shovel along on the bottom of the hearth to the center of the fire, and then raise it straight up through the fire (see Fig. 432). The clinkers can then be easily seen and removed. Most of them will stay on the shovel.
After the cinders and clinkers are removed, rake coke back into the center and pack it down. Add fresh coal to the back and sides of the fire if needed.
Lining a Forge. Lining a forge hearth with clay, although generally not practiced, will protect it against overheating and rusting and will increase its useful life. A forge hearth may be lined as follows:
- Make a thin wash of clay, preferably fire clay, and spread it over the inside of the hearth and allow it to dry.
- Then mix fine sieved coal ash and clay together, using 1 part of coal ash to 3 parts of clay. Make the mixture about as stiff as putty, and apply it about one inch thick around the tuyere opening and at least 8 in. on the sides.
- Allow it to dry over night.
- Then build a wood fire and bake slowly for at least an hour, turning the blower a little every 10 or 15 min. to keep the fire going.
In using the forge, be careful not to break up the clay lining with the poker or shovel.
Heating Irons in a Forge
To heat irons in a forge fire, place them in the fire in a horizontal position, not pointing down (see Fig. 433). Be sure there is burning coke below the irons, on both sides of them, and on top of them. Keep the fire deep and compact. Irons heat much more rapidly and oxidize or scale off much less when heated in a deep compact fire than in a shallow, burned-out fire. Some scale will form in spite of a good fire, but the scale should be kept to a minimum.
Small thin parts heat much more rapidly than heavier and thicker parts. To prevent burning the thinner parts, push them on through the fire to a cooler place, or otherwise change the position of the irons to make all parts heat uniformly.
For forging mild steel or blacksmith iron, heat it to a good bright-red heat. Do not allow it to get white hot and sparkle. Sparkling indicates burning. Tool steel must not be heated as hot as mild steel. A bright-red or low-orange heat is hot enough for tool steel.
Fitting Tongs; Holding the Work. If tongs cannot be found to fit the work, reshape a pair by heating and hammering the jaws over the piece to be held. Poorly fitting tongs are a source of continual trouble and should not be used.
A considerable amount of work can be done without the use of tongs. An eyebolt, for example, can be made on the end of a rod 20 to 30 in. long and then can be cut off when finished.
Cutting with the Hardy
A blacksmith does much of his cutting of iron and steel on the hardy. Although the hardy does not leave quite as smooth a cut as a hack saw, it is quite satisfactory for most blacksmith work. It cuts faster and easier than a saw and is less expensive, as there are no blades to wear out or break.
To use a hardy, place it in the hardy hole (the square hole) in the anvil, lay the bar or rod on it at the point to be cut, and hammer it down against the sharp edge (see Fig. 434). Hardies may be used for either hot or cold cutting. Some smiths prefer to keep two hardies, one that is thick and stocky and tempered for cutting cold iron, and one that is thin for cutting hot iron. The hardy, like other cutting tools, works better if kept sharp. It may be ground like a cold chisel.
In cutting cold iron, the bar may be nicked deeply on two or more sides and then broken off by bending. In cutting hot iron, it is common practice to cut clear through from one side. Care must be taken, of course, not to let the hammer strike the cutting edge of the hardy, or else both the hammer and the hardy may be damaged. In finishing a cut on a hardy, strike that last two or three blows just beyond the cutting edge and not directly over it.
Cutting Tool Steel. Never attempt to cut tool steel in the hardened state. To cut it on the hardy, cut it hot – not cold – and handle it just like other iron or steel (except, of course, do not heat it above a cherry-red or low-orange heat).
When it is important to have a smooth cut, it is better to cut tool steel by sawing part way through with a hack saw, clamping in a heavy vise at the sawing line, and then breaking by hammering.
Estimating Amount of Stock Required. Often before cutting off a piece of stock, it is necessary to estimate the amount required for bends and curves. To determine the amount required for a piece of irregular shape, a small wire may be bent into the desired shape and then straightened out and measured. To estimate the length of stock required for pieces of regular shape, like circles and parts of circles, estimate the length of the center line. For example, suppose it is desired to estimate the length of stock required for a ring 3 1/2 in. inside diameter, the stock itself to be 1/2 in. thick. The length needed will be the length of the mid-line, halfway between the inside and the outside edges. This length will be equal to the mid-diameter, 4 in., times 3.1416, or approximately 12 1/2 in.
Bending and Straightening
In bending iron at the anvil, two points are most important:
- Heat the iron to a good bright-red heat, almost but not quite white hot, throughout the section to be bent.
- Use bending or leverage blows–not mashing blows.
Place the iron on the anvil so that it can bend under the hammer blows without being forced down against the anvil and mashed (see Fig. 435). If an iron is struck at a point where it is resting firmly against the anvil, it will be mashed instead of bent. A few moderately sharp blows are better than several lighter blows.
Making Square Bends. Make abrupt square bends over the face of the anvil near the chipping block where the corner of the anvil is rounded to prevent marring or galling the iron (see Fig. 436).
As soon as the iron falls below a good bending heat, put it back in the fire and reheat it. To bend an iron at a certain point without bending the adjacent section, heat it to a high red heat, and quickly cool it up to the place of bending by dipping into water. Then bend quickly by hammering or other suitable methods.
Bending Flat Bars Edgeways. A flat bar can usually be bent edgeways by heating and placing over the horn and bending the two ends down slowly, using the hands if the piece is long enough, or two pairs of tongs in case of short pieces (see Fig. 437). Sometimes the bending can be done easily by simply putting one end of the piece in the hardy hole and pulling on the other end (see Fig. 438). If the iron starts to buckle, stop bending at once and lay it on the anvil and straighten it. Hammering the outside edge of the iron when laid flat will tend to stretch it and therefore help with the bending. Once the bend is well started, hammering on edge around the horn is not so difficult. Be sure to always hold the stock firmly, either with the hands or with tongs, and to keep the part to be bent at a high red heat.
Straightening. Straightening can usually best be done on the face of the anvil. Be sure to hold the stock firmly, and to strike at points where it does not touch the anvil face. Sighting along the stock is the best way to test for straightness and to locate high points that need striking.
Striking with the Hammer. Success in blacksmithing depends largely upon ability to strike effectively with the hammer. Most blacksmithing requires heavy, well-directed blows. Where light blows are better, however, they should be used.
Strike light blows mostly with motion from the wrist (see Fig. 439A). Use both wrist and elbow action for medium blows (see Fig. 439B). For heavy blows, use shoulder action as well as elbow and wrist motion (see Fig. 439C).
To direct hammer blows accurately, strike one or two light taps first, to get the proper direction and feel of the hammer, and then follow with quick sharp blows of appropriate force or strength. It is also important to use a hammer of appropriate size. A heavy hammer on light work is awkward, and blows cannot be accurately placed. And using a light hammer on heavy work is very slow and tedious.
Bending and Forming an Eye. One of the most common bending jobs in the blacksmith shop is that of forming an eye on the end of a rod. The following is a good method of making such an eye:
- Heat the rod to a good red heat back for a distance of about 5 to 8 in., depending on the size of the eye.
- Quickly place the rod across the face of the anvil with just enough of the heated end projecting beyond the edge of the anvil to form the eye. For exact work, the length of hot iron that is to project over may be quickly measured with a metal rule (see Fig. 440A and B). Place the iron across the anvil well up near the horn where the edge is rounded.
- Bend the end down, forming a square bend, with a few well-directed blows (see Fig. 440C). Work rapidly before the iron cools. In finishing the bend, strike alternately on the top of the anvil and then on the front vertical side.
- Heat the end of the stock and start bending the tip end around the horn. Work from the tip back toward the stem (see Fig. 440D, E, and F). Keep the iron hot through- out the part being bent; otherwise the bending will be slow and difficult, and the iron will not bend at just the places desired. If the square bend at the juncture of the stem and eye tends to straighten out, it is an indication that the end of the stock is not being kept hot enough while being bent.
- Round the eye by driving it back over the point of the horn, noting carefully where it does not rest against the horn and striking down lightly in these places (see Fig. 440G). Keep the iron well heated.
- Center the eye on the stem, if necessary, by placing the stem flat on the anvil face with the eye projecting over the edge, and strike the eye. Have the stock well heated at the juncture of the stem and eye, but have the eye itself practically cold. Such a condition can be produced by heating the whole eye and then quickly cooling most of the rounded part by dipping in water.
Blacking. After forging a piece of iron, it is a good plan to black it by heating it slightly and rubbing it with an oily rag (see Fig. 441). Blacking gives the piece a better appearance and provides some protections against rusting. In blacking an iron, heat it just hot enough to burn off the oil that is rubbed on. It should not be red hot. If the iron is not hot enough, it will have a greasy appearance after rubbing with an oily rag.
Do not black tempered tools in this manner, as heating would draw the temper.
Twisting. Twisting is really a form of bending. Small pieces may be twisted by heating, clamping a pair of tongs on each end of the section to be twisted, and applying a turning or twisting force. To twist two larger pieces (say more than about 1/4 in. thick by 1 in. wide), clamp them in a vise and twist with a pair of tongs or a monkey wrench (see Fig. 442). Be careful to clamp the vise and the tongs or wrench at exactly the ends of the section to be twisted.
In twisting, work rapidly before the iron cools. For a uniform twist, the iron must be a uniform temperature. If the twist is to be confined to a definite section of the stock, it is a good plan to place center-punch marks at the ends of the section before it is heated.
Drawing and Upsetting Iron
Drawing is the process of making a piece longer and thinner. Two points are particularly important in drawing:
- Keep the iron at a good forging heat, a high red or nearly white heat.
- Use heavy, straight-down, square blows.
Many beginners make the mistake of striking a combination down-and-forward pushing blow, thinking that the pushing helps to stretch the metal.
Drawing may be done more rapidly over the horn than on the face of the anvil, as the round horn wedges up into the metal and lengthens it and there is less tendency for it to stretch in all directions. If a piece tends to get too wide, place it on edge and hammer it.
Keep the iron hot. Hammering after the red heat leaves is hard work and accomplishes little. Also, the iron is apt to split or crack if hammered too cold.
Drawing Round Rods. To make a round rod smaller, the following steps should be carefully followed:
- Make it four-sided, or square in cross section.
- Draw it to approximately the desired size while it is square.
- Make it distinctly eight-sided by hammering on the corners after it is drawn sufficiently.
- Make it round again by rolling it slowly on the anvil and hammering rapidly with light blows or taps.
An attempt to draw round rods without first going to the square section not only requires a lot of extra work, but usually results in a badly distorted and misshaped piece.
Pointing a Rod. To make a round point on a rod, first make a square tapered point. Then make it eight-sided, and finally round. In pointing a rod, the following suggestions are important:
- Work on the far edge of the anvil. The toe of the hammer is then not likely to strike the face of the anvil.
- Raise the back end of the rod.
- Strike with the toe of the hammer lower than the heel (see Fig. 443).
After the point is drawn, sight to see if it is centered, or roll the rod on a flat surface and see if the point wobbles up and down (see Fig. 444). A few well-placed blows of the hammer are usually all that is required to center the point.
Upsetting. Upsetting is simply the reverse of drawing, or the process of making a piece shorter and thicker. It is done when more metal is needed to give extra strength, as when a hole is to be punched for an eye. There are two main points to be observed in upsetting;
- Heat the bar or rod to a high red or nearly white heat throughout the section to be upset.
- Strike extremely heavy well-directed blows.
Light blows simply flatten and burr the end instead of upsetting the piece through the heated section. The extra-heavy blows needed for upsetting can best be struck by first striking a light blow or two to get the direction of striking and then following with an extra-heavy blow. If the bar starts to bend, stop and straighten it at once. Further hammering will simply bend it more instead of upsetting it.
Probably the best way to upset a short piece is to place the hot end down on the anvil and strike the cold end (see Fig. 445). The hot end, of course, may be up, but it is usually easier to upset without bending if the hot end is down.
Usually three heats are enough for upsetting a piece. When more than three heats are required, it is generally an indication that the iron has not been heated enough or that the hammer blows have been too light.
In order to thoroughly heat the part to be upset, and yet confine the heat to this part, heat the work somewhat further than the upsetting is to go and then it quickly back to the line of upsetting by dipping in water (see Fig. 446).
The end of a long bar may be upset by laying it on the anvil face, with the hot end projecting beyond the edge, and striking heavy blows endways with the hammer. If the bar is long and heavy enough, it may be upset easily by ramming the hot end against the face or the side of the anvil.