6 Blacksmithing

THE HEARTH

There are various types of hearth available for school use but the two most popular ones have back blasts, i.e. the air blast comes from the back. One has a water cooled tuyere and the other a dry tuyere. The type with the water cooled tuyere is the better one because those with dry tuyeres tend to burn away at the blast hole and require frequent replacement of the tuyere or tue iron. Figure 2, shows a part-section through the hearth. The hearth tools are shown above figure 1.

FUEL

Some smiths use coal and others coke breeze. The choice depends upon local custom. However, good blacksmith's coal is hard to obtain. The beginner is well advised to use coke breeze. This must be good smithy breeze, free from dust; a suitable size is known as "beans". Crushed or broken-up boiler coke or furnace coke is not suitable for forging.

The following points should be remembered:

1. Keep the fire in a small area. This is achieved by keeping the blast to a workable minimum.

2. Prevent the fire from burning hollow. The heat of the fire must be in the middle, just below the piece of metal being heated (see fig. 1). A hollow fire allows the blast air to oxidise the metal or may even burn it.

3. Remove clinker periodically. When clinker is cold it looks like crude black glass and makes a characteristic "clink clink" sound when touched with the fire tools. It is formed by the combination of oxygen and the impurities in the fuel.

The clinker forms just below the blast hole. The blast blows it on to the metal being heated to which it sticks, thus making forging difficult and dangerous because the clinker spurts out under the hammer blows. To remove the clinker turn off the blast for a few minutes to allow the clinker to solidify. It can then be hooked out in one piece with the poker which should be flattened and curved for the purpose (fig. 1). Knowing just where to find clinker and how to remove it without disturbing the fire too much is an art.

THE ANVIL

The London pattern anvil is the one most used and is shown in figure 3. Anvils for school work should not weigh under 1 cwt nor over q.\ cwt. (They are sold by weight.) The body of the anvil is usually made from wrought iron or mild steel with a top facing of hardened carbon steel. Smiths often like to stand the anvil on an elm trunk. This reduces the noise a little and gives it a certain amount of resilience. In school they are nearly always on stands. Some resilience can be obtained by using the plywood pad shown in figure 3.

TOOLS

Hammers

A 1 lb ball pein hammer is a good size for smaller people. Stronger people can manage a 2 lb hammer particularly if the haft is shortened. A 7 lb sledge hammer for heavy striking is needed occasionally.

Swage Block

This is a useful tool although good work can be done if one is not available. A useful size is about 12" x 12" X 6". These are used on a stand (fig. 3). It can be used in the vertical position or horizontally as shown by the dotted lines for shaping and swaging.

Floor Mandrel

These are available in a number of sizes and are made from cast iron. They are useful for round work like rings and hoops (fig. 3)

Leg Vice

Although inferior in its gripping action to the engineer's parallel jaw vice, it is useful for heavy bending and withstands hammering (fig. 3).

Tongs

These are selected to suit the work. Traditionally a black­smith makes his own tongs, but for school use they are bought ready made. A useful selection is shown in figure 4. Closed mouth tongs are used for thin metal. Usually these have a vee groove along the inside of the jaws for holding small section, round or square, metal.

Open mouth tongs are used for holding flat strip metal.

A tong ring can be slipped over the end of the tongs to keep the work gripped. This is useful when forging the end of metal
about 8" long, as time is wasted retrieving it from the hearth.

Hollow bit tongs (also known as round bits) are used for round or square metal.

Large bolt tongs often used in school for lifting small crucibles of molten metal from the forge when small castings are being made.

Rivet, sidebit or ring tongs are used to hold round work at right angles to the tongs.

Box tongs are used for holding flat strips securely.

The universal tongs are probably the most useful. They have a vee groove along the inside of the jaws as well as the openings at the side.

PROCESSES—BEGINNINGS

Most learners try to forge metal when it is not hot enough or continue hammering it long after it has lost its proper heat. This often results in splitting.

Overheating resulting in burnt metal (particularly on thin section material) is another hazard for the beginner.

A beginner should see a piece of metal, say 3/8" square mild steel about 3 feet long, heated up and withdrawn from the fire from time to time to observe the temperatures. Finally it should be heated until the end starts to burn and becomes completely spoilt. It is far better to see this happen and to learn to judge the temperatures on a waste piece of metal than to spoil part of a job.

A good heat for most simple forging operations on mild steel is a bright red heat. This is considerably hotter than the heat at which we harden carbon steel and slightly higher than the average temperature used in brazing.

Another important point is that the fire should be disturbed as little as possible when the work is taken out and inserted.

Holding the hammer properly is another consideration. Do not hold the hammer too near to the head.

Drawing Down and Flaring

Drawing down is a process of thinning the metal at the end either by increasing its width or reducing it on all sides and making it longer. A round taper is a variation of this (fig. 5).

The beginner must beware of splitting and piping. Splitting can be caused by hammering the metal when it is too cold or by faulty hammering. Piping is the forming of a hollow centre on the end of the bar or rod (fig. 6). This can be avoided if a blunt taper is first made on the end of the rod (figs. 5 and 7). An example of flaring is shown in figure 8.

Bending

This can be done in the leg vice or on the anvil, or with bending horns and a wrench.
Small section metal can be bent in the leg vice but it is essential to work quickly, before the jaws have taken too much heat from the metal.

A centre punch mark on the metal will show where to hold it in the vice (fig. 10). Blacksmiths make up their own bending jigs and tools for more complicated work, particularly where a number of units are required.

These methods cause the metal to stretch on the outside of the curve and so become thin (fig. 10).

Bending without thinning can be done as shown in figure 9 on the anvil.

First a centre punch mark must be made. Then heat and bend to 45°, as shown. Next upset. Then complete the right angle as shown.

The bending of an eye as on the handle of a poker needs a little consideration. The length of metal needed to form the eye must be estimated. One method is shown in figure 11 (1). The dotted line shows the length of metal required.

The metal is then heated and bent at right angles as shown in figure 11 (2). Now reheat the metal and withdraw from the fire and quench the metal at the bend by dipping in the trough or with water poured from a can (fig. 11 (3)). Now bend on the bick as shown in figure 11 (4). Next reverse the work and continue shaping as shown in figure 11 (5). Close up the eye by tapping lightly round the outside of the eye (fig. 11 (6)). A good eye should be circular and should have its centre over the centre of the shaft.

Horns and Wrench

These are used for scrolls or other gentle curves. The metal is heated and the work is bent as shown in figures 12 and 13.

Twisting

This is a form of decoration often used on square metal, but metal of other sections can be twisted. The type of twist is influenced by the heating. A good red heat over a long length will give a long gradual twist, but if the bar is heated more intensely over a short length a short sharp twist is produced.

Twisting should be done at one heat because it is difficult to obtain an even twist if the metal has to be returned to the fire. Care must be taken to keep the metal straight. For long bends or double twists a tube can be put over the metal as a sleeve. This must be an easy fit otherwise when the metal is twisted it is difficult to remove. This method is used by beginners.

It is not wholly satisfactory because the actual twisting cannot be observed. Another method of obtaining a long even twist is to have an assistant who pours a little water on to those parts that are twisting too quickly. Long twists can also be kept in alignment by using a rest as shown in figure 12A.

Scrolls

These are usually in the form of a "C" or an "S". It is usual to make these by using a scroll tool which should be made after having gained experience in making a scroll by hand. The method of making a scroll by hand is shown in figure 12. First draw the metal down, keeping the width the same over the entire length. Next start the bend as shown.
When the metal needs reheating remember to heat the part which needs bending. Continue to bend the scroll using the close spaced horns as shown. A small scroll often needs a number of heats when being made by a boy.

Scroll Tool

These can be made in the same way as the scroll just men­tioned except that they are made from stouter metal—3/4" x 3/8" is a good size. The end is flared on one side only. This is so that the centre of the scroll tool is higher than the rest of the tool to allow the first part of the bend to be made in the scroll as shown in figure 13.
Scrolls made on the scroll tool are started off as in figure 12. Then they are put on the centre of the scroll tool and held with
round nose pliers and bent round. They are finished by using a wrench (fig. 13). Finally the scroll should be placed on the flat face of the anvil and lightly tapped to make it level.

Upsetting or Jumping Up

This is the reverse of drawing down. A good heat is needed; a slightly higher temperature than that used for simple forging operations. The process is made easier for boys if the end of the metal is prepared as shown in figure 14 before upsetting, particularly on small section metal, as this allows the thrust of the blow to be central. (This applies only to metal to be upset at the end.)

The upsetting can be done by striking the end of the metal on the face of the anvil as at A, or on the side (B), or on a chipping block on the floor (C), or with a hammer on the anvil if the work is short enough (D).

Any bend that occurs must be straightened out at once. The metal must then be reheated and the process continued. It helps if the tip of the bar is quenched before continuing with the upsetting. This allows the thickening to take place away from the very end. If the thickening is required in the middle of the bar then that part must be heated. The metal on either side of the area to be upset can be cooled by water poured from a can.

Swaging

This is usually a process of finishing the cross section of the work to size and shape. Top and bottom swages are usually used as shown in figure 15. For larger work the swage block can be used (fig. 3).

Fullering

This process can be used for thinning down the metal by making grooves or hollows across it. This is usually done by using top and bottom fullers as shown in figure 15. If the thin­ning is required on one side only the top fuller can be used on its own with the work resting on the anvil.

The Hardie or Anvil Cutter

This is used in the hardie hole. The metal is cut partly through from either side then tapped with the hammer over the edge of the anvil to break it (fig. 16).

Hot Chisel and Cold Chisel

These are known as hot or cold depending on whether they are used to cut hot or cold metal. Hot chisels are not hardened and tempered because the heat from the metal being cut would soften them. They are ground to a cutting edge of 300 and are long enough to keep the hand well away from the hot metal as shown in figure 17. Cold chisels are hardened and tempered and ground to 60°.

For large work the chisels are fitted with either wooden handles or metal rods as shown, and are often known as sets (fig. 17).

Punches for Hot Work

These can be round or square or any shape. They should be long enough to keep the hand away from the hot metal. Large ones can be rodded. Figure 18 shows a punch being used. The punch is first driven into the metal then removed and quenched. The metal is then turned over and punched from the other side on the chilled spot where the metal has been under pressure against the cold anvil. The billet shown should drop out.

Greater strength of the forged metal can be obtained by using first a slot punch then a drift as shown (fig. 19). This is because less metal is removed with a slot punch.

Drifts

These are similar to punches and are used to open up punched holes, smoothing and shaping them at the same time (fig. 19)

Flatters and Set Hammers

These are used to smooth out the work after hammering and to get into sharp or radiused corners (fig. 20).