Material. Railway-line steel; motor-vehicle axle shafts (half shafts); square-section spring steel or mild steel if treated as in Job 18, or even a piece of old ox-plough beam of solid section.
Additional tools. Slot punch and drift (it is best to have a drift of about 200 mm for ease of handling); old bastard file or rasp; grinder, if possible.
In some forging operations a ball-peen hammer is useful. The easiest type to make is that shown in Fig. 159B. If you look back at Job 14 (the set hammer), you will see that the eye is left with as much metal as possible around it in order to withstand being hit with powerful hammer blows. In hand hammers, this thickness of metal is not needed.
It is important that the eye taper toward the centre from both sides so that the shaft can be securely wedged into position. To do this, the eye drift is tapered as shown (Fig. 160B). The material size depends upon the weight of hammer required, but for practice a 30 x 30-mm square is suggested.
If possible, use a hand length of material. This is easier to handle than a shorter length held in tongs. Mark out as in Fig. 158A with prominent centre-punch marks on both sides of the piece. Take a yellow heat and slot punch from both sides as in Job 14. Reheat and cool the end slightly, and upset to open the eye as in Job 14.
While the job is hot, hammer in the drift quickly from alternate sides but not to its full depth. Leave about 15 mm of the tapered end of the drift still to go. Reheat to a yellow heat and flatten the sides of the eye on to the drift (Fig. 161). Work alternately from each side. As the flattening proceeds, the drift is driven farther in to the eye, again working alternately from each side until the full size and correct shape of eye are obtained.
When the eye is correctly formed, reheat the end and forge (Fig. 162) to a square section, then remove the corners to give an octagonal section about 22 mm across the flats. With a sharp hot set, cut off any surplus material to leave a length of 35 mm from the rim of the eye (Fig. 163). Cut all around the piece equally from all sides. This will leave a slightly pointed end that will require little finishing to give a neatly radiused shape to the ball-peen. Final finishing of this end can be carried out by grinding or filing. If a good rasp or old bastard file is at hand, most finishing can be carried out by quickly filing or rasping the job while at a good yellow heat, the final finish being done when it is cold.
If any deformation of the eye has occurred during the drawing-down and cutting, this should be corrected by gently tapping the drift back into the eye from either side. Next, with either hand hammer or set hammer (Fig. 164), the face end of the hammer head is set down over the edge of the anvil and drawn-down to slightly less than the original 30 mm, after which the corners are slightly flattened. The distance across the flats should be about 28 mm.
With a sharp hot set, cut the hammer head off the bar, leaving the face as flat as possible. If the set you use is sharpened from one side only, this will help to keep the face flat. Again, this face may be rasped while hot. Reheat to red heat all over and allow the head to cool in sand, lime or ashes. When it is cool, finish the face with a grinder or file.
If the hammer is made of spring steel, it can be hardened and tempered by heating to a dull red heat, holding it with tongs through the eye and quenching the face and the peen in turn in oil. They should be repeatedly quenched one after the other until the eye is quite cool (the eye must never enter the oil). Then the whole job can be finally cooled.
Clean up both face and peen, heat a drift to a bright red heat and place it firmly in to the eye. Heat will be conducted from the drift to the hammer head. Watch for the oxide colours to appear. When a dark brown, almost blue, is seen, quench the faces in water in the same manner as above. It is likely that the colours will appear on the peen end first. Look out for this and quench that end while waiting for the colours to appear on the other, then quench alternately as before.
If railway steel is used for the head, adopt a similar technique but quench it as soon as a light brown appears. If the job is made of motor-vehicle axle shaft, quench it in oil from a dull red heat. If mild steel is used, see Job 18. Finally, clean up the face and peen with a fine grinding wheel or emery cloth. Fix a good wooden shaft to fit the user's hand. It should be about 500 mm long for anvil work.