Plane irons and chisels are sharpened in pre­cisely the same manner, so that a description of sharpening only one—the plane iron—will be given.

Fig. 48 —Taking the Plane Irons Apart

Release the plane iron and cap from the throat of the plane by lifting the cam on the cap. Separate the plane iron and cap iron—do not remove the cap screw, but slide the plane irons lengthwise until the screw head will pass through the opening made for it, as shown in Fig. 48. Place a little oil on the stone and, holding the plane iron as shown in Fig. 49, proceed to whet the cutting edge. The iron must be held neither too high nor too low.

Fig. 49— Proper Pitch of Iron



If held too high, the edge will be blunted and ruined, and a new edge must be ground on the grindstone. If held too low, the whetting takes place on the heel of the bevel and does no good, since it does not allow the stone to touch the edge of the plane irons. To tell when the tool is at the correct angle, draw the oil to one spot in the center of the stone. Place the iron with the bevel in the oil and the rear end down so the iron is flat, or nearly so, on the stone (Fig. 50). Gradu­ally raise the rear of the iron until the oil can be seen to spurt from under the cutting edge. The iron is then in position. Now move the iron either back and forth the full length of the stone or give it a circular motion, in either case striving not to change the angle at which it is held.

After the whetting has been continued for some time, considerable pressure having been applied, and the test for position having been frequently made, a rubbing of the fingers down over the face side and out
over the cutting edge will reveal a "wire edge." This must be removed before the iron is used again. To do this, hold the plane iron, face down, so that it touches the stone along its whole length, and give it a forward and downward movement on to the stone (Fig. 51). This generally bends the wire edge under and cuts it off. Sometimes, however, it simply bends it back on the bevel. In this case the bevel must be whetted again slightly to bend the wire edge back on the face, when the above operation may be repeated. Some­times it takes several turnings to remove the wire edge. After the wire edge has been removed, the plane irons must be tested for sharpness. There are several ways of do­ing this. One way is to hold the iron up to the light; if a white line appears, the edge is blunt and should be whetted more.

Another way is to draw the edges of the plane irons along the thumbnail, feeling for friction. If the iron is sharp, it will cut the nail slightly and the resulting friction will be perceived by the worker. If the iron is dull, there will be no cutting and therefore no friction, in which case more whetting will be necessary.

A mechanic generally uses the second method, but instead of the thumbnail he uses the ball of the thumb (Fig. 52). This is a more sensitive test and therefore more satisfactory. The ball of the thumb is calloused and if slight pressure is applied as the edge is drawn along the thumb, no harm need be done. When the edge is found satisfactory, put the plane irons and the cap irons together and place them in the throat of the plane.

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