Blacksmithing Secrets Part 2
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.
Punching Holes in Hot Iron
It is sometimes easier to punch a hole in a piece of iron than to drill it; and for some purposes a punched hole is better. For example, in forming an eye on the end of a bar in making a hook or clevis, punching makes a stronger eye. Very little metal is wasted when a hole is punched. To punch a hole, proceed as follows:
- Heat the iron to a good working temperature, a high red or nearly white heat.
- Place the hot iron quickly on the flat face of the anvil — not over the pritchel hole or hardy hole. Punching over a hole would stretch and bulge the iron.
- Carefully place the punch where the hole is to be, and drive it straight down into the metal with heavy blows until it is about two- thirds of the way through (see Fig. 447A).
- Turn the iron over, and drive the punch back through from the other side (see Fig. 447B). Be sure to locate the punch so that it lines with the hole punched on the first side. Reheat the iron and cool the punch as may be needed.
- Just as the punch is about to go through, move the piece over the pritchel hole or hardy hole to allow the small pellet or slug to be punched out (see Fig. 447C).
- Enlarge the hole to the desired size by driving the punch through the hole first from one side and then the other. Always keep the metal at a good working temperature, reheating as may be necessary.
When punching holes, cool the punch frequently by dipping it in water (see Fig. 448). A little powdered coal dropped into the hole will help keep the punch from sticking.
An easy way to place the punch so as to get the hole centered in a bar is to lean it and twist it slightly until it is in the correct position. Although a hand punch can be used in punching hot iron, it is much better to use a regular blacksmith’s punch with a handle in it.
Forming Punched Eyes. Usually, although not always, when a hole is to be punched for an eye, as in a chain hook or a clevis, it is best to upset the stock first so as to give more metal and make a stronger eye.
After upsetting, the end is shaped and the corners are rounded before punching. This can best be done by forming a neck or shoulder just back of the eye by hammering over the far edge of the anvil, as shown in Fig. 449A. The end is then further shaped and the corners rounded by working over the anvil as suggested in the various other views of Fig. 449. Having the end thus shaped, the hole may be punched in the usual fashion.
For a clevis, the punched holes should be left with straight sides to fit the clevis pin. Holes in chain hooks, however, should have the ends flared and rounded somewhat to fit better in chain links. To thus shape an eye for a chain hook, place the eye at an angle on the end of the anvil horn and make the stock approximately eight-sided and finally round by rolling it slowly while striking light rapid blows. (See Fig. 450).
Points on Forging
- A clean, deep, compact fire is the first requirement for good blacksmithing.
- Put the irons in the fire in a horizontal position — never point them down into the fire.
- Always work the irons at a good forging heat — a bright red or nearly white heat for mild steel.
- In bending, use bending or leverage blows — not mashing blows.
- In drawing, strike square direct blows straight down — not forward-pushing or glancing blows.
- In drawing round rods, always make them square first and do the drawing while square. When drawn sufficiently, make them eight-sided and finally round.
- To smooth up a round rod, roll it slowly on the anvil while striking a series of light quick blows.
- In pointing rods, work on the far edge of the anvil. Raise the back end of the rod, and strike with the toe of the hammer tilted down.
- In upsetting use a high heat, and strike extra-heavy blows.
- To make a good twist, have the section to be twisted at a uniform temperature.
- To punch a hole in a hot iron, start in on the flat face of the anvil. Then turn it over, and drive the punch back from the other side. Move the iron over a hole in the anvil face for finally driving out the pellet.
- In cutting on the hardy, be careful not to let the hammer strike the cutting edge.
- Use the chipping block for cutting with the cold chisel — not the flat face of the anvil.
- Strike light hammer blows with wrist motion only; medium blows with motion from both the wrist and the elbow; and heavy blows with motion from the shoulder, wrist, and elbow.
- Blacking a forging gives it a better appearance and provides some protection against rust. To black, simply rub the piece with an oily rag when it is just enough to make the rag smoke.
Working Tool Steel
One of the main advantages of having a forge in the farm shop is to be able to redress and make and temper tools like cold chisels, punches, screw drivers, picks, and wrecking bars. Tool steel for making cold chisels and punches and similar tools may be bought from a blacksmith or ordered through a hardware store; or it may be secured from parts of old machines, such as hay-rake teeth, pitchfork tines, and axles and drive shafts from old automobiles.
Heating Tool Steel. Always heat tool steel slowly in a clean, deep coke fire. Uneven heating, which is usually caused by heating in a poor shallow fire or by too rapid heating, results in unequal expansion, which, in turn, may cause internal flaws or weaknesses in the steel.
Never heat tool steel above a bright-red or low-orange heat, and heat to this temperature only for heavy hammering. Heating higher is likely to cause the steel to become coarse-grained and weak, rather than fine-grained and strong. In case a piece of tool steel is heated a little too hot, the grain size may be restored by (1) allowing it to cool slowly and then reheating, being careful not to overheat it again, or (2) by heavy hammering at a bright-red or low- orange heat.
Forging Tool Steel. It is important to observe the following points when forging tool steel:
- Do not hammer below a red heat, as this may cause cracking and splitting.
- Be sure tool steel is uniformly heated before it is hammered. Otherwise, the outside parts, which are hotter, may stretch away from the inside parts, which are colder, and thus cause internal flaws.
- Avoid very light hammering, because this may draw the outer surface without affecting the inner portions.
- Do as much forging as possibly by heavy hammering at a bright-red or low-orange heat, as this will make the grain size smaller and thus refine and improve the steel.
- When finishing a piece by moderate blows, do not have the steel above a dark-red heat.
Annealing Tool Steel. It is best to anneal a tool, or soften it, after it has been forged and before it is hardened and tempered. This is to relieve strains that may have been set up by alternate heating and cooling and by hammering. To anneal a tool, heat it to a uniform dark-red heat and place it somewhere out of drafts, as in dry ashes or lime, and allow it to cool very slowly.
Hardening and Tempering Tool Steel. If tool steel is heated to a dark red and then quenched (cooled quickly by dipping it into water or other solution), it will be made very hard. The degree of hardness will depend upon the carbon content of the steel and the rapidity of cooling. The higher the carbon content, the harder it will be; and the more rapid the cooling, the harder it will be.
A tool that is hardened in this manner will be too hard and brittle and must be tempered or softened somewhat. This may be done by reheating the tool to a certain temperature (always lower than the hardening temperature) and quickly cooling it again. The amount of softening (or tempering) accomplished will depend upon the temperature to which the tool is reheated. For practical purposes in the farm shop, these temperatures are judged by the color of the oxide or scale on the steel as it is being reheated. A straw color, for example, indicates a comparatively low temperature, and if the tool is quenched on this color, it will be softened only a little. A blue color, on the other hand, indicates a higher temperature, and if the tool is quenched on this color, it will be made considerably softer.
Different grades of tool steel will have different degrees of hardness when quenched at the same color. Therefore, it may be necessary to experiment a little with the first piece of a new lot of steel in order to secure the desired degree of hardness.
Hardening and Tempering A Cold Chisel. After a cold chisel is forged and annealed, it may be hardened and tempered as follows:
- Heat the end to a dark red, back 2 or 3in. from the cutting edge.
- Cool about half of this heated part by dipping in clean water and moving it about quickly up and down and sideways until the end is cold enough to hold in the hands (see Fig. 451A).
- Quickly polish one side of the cutting end by rubbing with emery cloth, a piece of old grinding wheel, a piece of brick, or an old file (see Fig. 451B).
- Carefully watch the colors pass toward the cutting end. The first color to pass down will be yellow, followed in turn by straw, brown, purple, dark blue, and light blue.
- When the dark blue reaches the cutting edge, dip the end quickly into water and move it about rapidly. If much heat is left in the shank above the cutting edge, cool this part slowly so as not to harden the shank and make it brittle. This is done by simply dipping only the cutting end and keeping it cool while the heat in the shank above slowly dissipates into the air.
- When all redness has left the shank, drop the tool into the bucket or tub until it is entirely cool.
When the tool is first dipped, it is important that it be moved up and down to prevent the formation of a sharp line between the hardened and unhardened parts, as such a line might cause the tool to break at this point sometime later when in use.
If the colors come down too rapidly, the tool may be dipped into the water and out again quickly to retard their movement. When they move down slowly, it is easier to watch them and do a good job of tempering.
Dipping the end at the beginning of the hardening and tempering process makes it very hard. The heat left up in the shank of the tool, however, gradually moves down to the cutting end and softens it; and when it is softened to the desired degree of hardness, as indicated by the color, the tool is then quickly quenched to prevent any further softening. The various colors are simply indication of different temperatures.
If a tool is tried and found to be too soft, as indicated by denting, it should be retempered and the final quenching made before the colors have gone out quite as far as they did originally, that is, before the end has been softened quite as much. In case a tool prove to be too hard and the edge chips or crumbles, it should be retempered and the colors allowed to go out a little further.
Tempering Punches, Screw Drivers, and Similar Tools. Tools like punches, screw drivers, and scratch awls may be tempered in the same manner as a cold chisel but may be made harder or softer according to the requirements of the tool. A scratch awl should be made
somewhat harder than a cold chisel, a rock drill somewhat harder, a center punch just a little harder, a punch for lining up holes
somewhat softer, a screw driver somewhat softer, etc.
Tempering Knives. Knives and tools with delicate parts are usually hardened and tempered in a manner slightly different from that used for cold chisels, in order to avoid the danger of overheating and warping and to ensure uniform hardening and tempering of the cutting edges.
After a knife blade is forged, anneal it. Then heat it slowly and uniformly to a dark red. Then cool it quickly by dipping the blade edgewise, thick edge first, in clean tepid water or oil. This method of cooling helps to ensure uniform cooling and therefore uniform harden- ing and freedom from warping. Next polish the blade and then reheat it by drawing it back and forth through a flame or by laying it against a large piece of red-hot iron and turning it frequently to ensure uniform heating. When the desired color, usually blue, appears, quickly cool the blade again by dipping edgewise in the water or oil.
Another method of heating knives and similar tools for hardening and tempering is to draw them slowly back and forth inside a pipe in a forge fire. The pipe must first be uniformly heated in a big fire and then turned frequently to keep it uniformly heated on all sides. Do not allow the knife to touch the pipe.
Points on Working Tool Steel
- Use a clean deep coke fire for heating tool steel, and heat it slowly and evenly.
- Heating in a poor shallow fire, or heating too rapidly, is likely to cause uneven heating, which results in unequal expansion, which in turn may cause internal flaws or cracks.
- Proper hammering of tool steel at the proper temperature refines it, making the grain size smaller.
- Do not hammer tool steel unless it is at least at a dark-red heat and heated uniformly clear through.
- Hammering below a red heat is likely to cause cracking and splitting.
- Hammering when not heated clear through may cause the outer parts to stretch away from the inner parts and cause internal flaws or cracks.
- Avoid light hammering even when the steel is well heated, because of danger of drawing the outer surface without affecting the inner parts.
- Never heat tool steel above a bright-red or low-orange heat, and then only for heavy hammering.
- For moderate hammering, as in finishing and smoothing a job, do not heat above a dark red.
- Tool steel is ruined if it gets white hot.
- In case tool steel is accidentally overheated somewhat, allow it to cool slowly and then reheat, being careful not to overheat it again; or heat it to a bright-red or low-orange heat and forge by heavy hammering to restore the fine grain size.
- After a tool is forged, anneal it by heating to a uniform low red and placing it in dry ashes or similar material to cool slowly.
- 13. In quenching a tool like a cold chisel, move it about rapidly up and down and around — to prevent a sharp line of demarcation between the hot and cold parts.
- 14. Tempering colors should move slowly so they may be easily seen. If they move too fast, dip the tool quickly into water for an instant.
- 15. In the final quenching of a tool like a cold chisel, cool the end quickly but dissipate any heat left in the shank very slowly. Otherwise, the shank may be hard and brittle.
- 16. In case a tool is found to be too hard, retemper it and allow the temper colors to go out a little further before final quenching.
- 17. In case the tool is too soft, quench before the colors go so far.
Welding in the Forge
Although welding in the forge is somewhat more difficult than ordinary forge work, welding of links, rings, and bars and rods is not particularly difficult if careful attention is given to the fire and to a few simple precautions.
A good fire is the first requirement for welding in the forge. It is important for any blacksmithing work, but for welding it is indispensable. Poor fires account for most of the difficulties experienced by beginners. Clean the fire about every half hour when welding.
Scarfing the Irons. Ends to be welded should first be properly shaped or scarfed. Scarfed ends should be short, usually not over 1 1/2 times the thickness of the stock. They should also have rounded or convex surfaces (see Fig. 452), so that when they are welded together any slag or impurities will be squeezed out rather than trapped in the weld. Avoid long, thin, tapering scarfs, because they are easily burnt in the fire, and because they cool and lose their welding heat very rapidly when removed from the fire, thus making welding exceedingly difficult. The ends of bars and rods should usually be upset before they are scarfed.
Heating the Irons. Heat the irons slowly at first so they will heat thoroughly and uniformly. Turn them over in the fire once or twice during heating to ensure equal heating of all sides and parts.
After the irons reach a bright-red heat, remove them and sprinkle welding compound or flux on the scarfed ends (see Fig. 453). Then replace the irons in the fire, and quickly bring them to the welding temperature. At this point, it is especially important that the fire be deep and compact. Otherwise, it will be difficult or impossible to heat the irons to the welding temperature. If one iron heats faster than the other, pull it back into the edge of the fire for a few seconds. They should reach the welding heat at the same time. During the last part of the heating period, have the scarfed sides of both irons down so that they will be fully up to the welding temperature when removed from the fire.
When the irons reach the welding temperature, they will be a brilliant, dazzling white; their surfaces will appear molten; and a few explosive sparks will be given off. It is then time to remove them from the fire, get them in place quickly on the anvil, and weld them together.
Getting the Irons Together. When the irons reach the welding heat or temperature, remove them from the fire, quickly rap them over the edge of the anvil to shake off any slag, place them together, and hammer them in place (see Fig. 454). Strike medium blows at first, because the iron is soft and is easily mashed out of shape. Follow with heavier blows. Fast, accurate work is required, or the irons will lose their welding heat before they can be joined.
In placing the irons together on the anvil, put the right-hand one down first, and then put the left-hand one down on top of it. The pieces can thus be held together with only one hand, leaving the right hand free to use the hammer. Steadying the pieces over the edge of the anvil will help get them accurately and quickly placed together (see Fig. 454). It is a good plan for the beginner to practice bringing the irons out of the fire and placing them together a few times before taking the welding heat. Pieces that are long enough to be held in the hands without tongs are handled more easily than short pieces.
If the irons do not stick at the first attempt, do not continue hammering, but reshape the scarfs and try again, being sure that the scarfs are properly shaped, that the fire is clean, and that it is deep and compact. Irons will not stick if there is clinker in the fire or if it burned low and hollow. It is generally not possible to make irons stick after two or three unsuccessful attempts because they will most likely be burned somewhat, and burned irons are difficult or impossible to weld. In such cases, cut off the burned ends before rescarfing.
Finishing the Weld. If, as is often the case, the irons stick but the lap is not completely welded down on the first heat, simply reapply flux and take another welding heat. In taking an extra heat, be sure to have the lap down in the fire just before removing for placing on the anvil and hammering.
After a weld is completed in a round rod, the welded section may be easily smoothed and drawn to size by first making it square; drawing as may be required while it is square; and then making it eight-sided and finally round, in the same manner as drawing round rods.
Welding a Link or Ring. To make a link or ring, heat the stock and bend it into a horseshoe or U shape (see Figs. 455 and 456). Then heat and scarf the ends in the following manner:
- Place an end diagonally across the shoulder between the anvil face and the chipping block. Keep the other end against the vertical side of the anvil (see Fig. 457).
- Strike a medium blow to the end on the shoulder. Swing the tongs a little, and strike another blow. In a similar manner, swing the tongs and strike again. This makes a short, blunt, angling taper with a slightly roughened surface.
- Turn the piece over, and scarf the other end in the same manner.
- Finish the scarfs by striking lightly with the cross peen of the hammer.
After scarfing the ends, heat and bend them over the horn and lap them together. Be sure the ends meet each other at an angle of about 90 deg. This ensures plenty of material for finishing the link and prevents a thin, weak weld.
Next, heat the link, apply flux, and then take a welding heat. When the welding heat is reached, remove the link quickly from the fire, rap it over the edge of the anvil to shake off any slag, place it flat on the anvil (not on the horn), and hammer. Strike one or two medium blows, turn the link over, and strike a few medium blows on the other side. Follow with heavier blows. Take one or two more welding heats if necessary.
After the link or ring is welded, finish it at a good forging heat over the horn. Roll it slowly by twisting the tongs back and forth (see Fig. 458), while hammering rapidly with light blows. In case of a large ring, finish by making the stock square, then eight-sided, and finally round, as in drawing rods.
Points on Welding in the Forge
- Use a clean, deep, compact coke fire.
- Clean the fire every half hour.
- Make the scarfs short and thick, rather than long and thin. Scarfs should not be longer than 1 1/2 times the thickness of the stock.
- Round the surfaces of scarfs so slag will be squeezed out rather than trapped in the weld.
- Heat the irons to a good welding heat, yet do not burn them.
- Bring both irons up to the welding heat at the same time.
- Before welding the irons together, shake off any slag or impurities by quickly rapping the tongs over the edge of the anvil.
- Strike light or medium blows when irons are at the welding heat. Simply forcing the parts together is all that is necessary. Heavy blows mash the irons.
- In case of failure to stick do not continue hammering. Reshape the scarfs, reflux, and try again, being sure the fire is in good shape and that you heat the irons hot enough.