After edge tools have been whetted several times the cutting edge becomes so blunt that it is necessary to remove a considerable portion of the end in order to maintain the proper cutting angle. This is accomplished by using a grindstone or emery grinder suitable for this sort of grinding. Grindstones are not likely to injure the tools if properly supplied with water. Emery wheels are often so hard, and run at such a speed that they will spoil the tools unless one understands thoroughly how to use them.

Ordinary grindstones are cut from natural sandstone. They vary greatly in quality. Some are much harder than others. Some are composed of particles of sand which are quite hard and sharp while others do not have this keen cutting quality. All wear more or less uneven by use and it is therefore necessary to be careful in using them. Always try to grind down the high places and in grinding small tools such as narrow chisels and gouges you must keep them moving across the face of the stone. If the grindstone were in perfect con-dition there would be little trouble about grinding tools. This however is almost never the case and you must there-

Fig. 156. Grinding.

fore learn to grind on grindstones that are very much out of order. This is not so difficult a task as you may suppose. The best way is to learn to hold the tools freehand as shown in Fig. 156. This does not require a great amount of practice and when once learned will enable you to grind on almost any grindstone in a very satisfactory manner.

Be careful to hold the tools firmly and at the proper angle. Grind back from the edge first and finish by grinding at the edge until the basil surface is straight, flat, and to an edge. The flow of water will help to indicate how the stone is cutting. The stone or emery wheel should revolve towards the edge of the tools as indicated by the arrow. One hand presses the tool to the stone and the other hand controls the angle. The motion of the stone has a tendency to roll the chisel or plane bit in such a manner that it will be cut too much at the upper corner. The hand which controls the tool must tend to roll it so it will tend to cut most at the lower corner. Grind very carefully and examine the tool often to see just how the stone is grinding. You must not expect to grind the edges of chisels, planes, and similar tools sufficiently fine for use. The grindstone is to remove the large quantity of material and give the proper shape and angle to the basil surface. The whetstone and strop must be used to produce the keen cutting edge.

The directions for whetting chisels and planes are given under the descriptions of these tools.