Sharpening Appliances

Although both wood and metal-working tools are in many instances sharpened entirely by hand on the grinding wheel or bench stone, greater accuracy in the formation of the cutting edge can be obtained by using a guide, or jig, to maintain t^e tool in correct angular alignment with the surface of the abrasive stone or wheel.

With long practice, the carpenter is able to sharpen his tools free-hand to cut to his satisfaction, but this may be far from being the case where the novice is concerned.

Even the experienced mechanic can hardly be expected to grind a small twist drill by hand to that extreme degree of accuracy which is essential if the drill is to cut a hole truly aligned and exactly to size.

Bench-Stone Jigs. Edged-tools such as wood chisels and plane irons, and also scrapers used for metal work, have their cutting edges formed by grinding away the tip of the tool to an angle. This angle varies with the use to which the tool is put, and although it should be as acute as possible to. promote free-cutting, it must at the same time afford sufficient strength for the cutting edge to stand up to the work imposed. Thus, a greater or more obtuse angle is required for a firmer wood chisel, which is struck by a mallet, than is necessary for a paring chisel worked only by hand pressure. Again, the angle given to the metal scraping tool Ziould be such that it does not tend to dig into the surface when applied to the work.

The most suitable angles for edged-tools have been determined by long experience, and for wood-working tools, with which, for the moment, we are chiefly concerned, these lie between 25 and 45 deg.

In order that tools may be accurately sharpened to these angles, various jigs for use in connection with the bench stone have been devised. Fig. 7 shows a jig used

Fig. 7.

for sharpening plane irons and wood chisels, and Fig. 8 illustrates the method of using the jig on the bench stone.

It will be apparent that the angle formed at the cutting edge depends on the distance to which the tool is set out from the clamp. Another device designed for similar operations is depicted in Fig. 9, and, here, the angle honed on the tool is adjusted by means of the screw that forms part of the roller component.

Fig. 9.

The most convenient method of setting the tool correctly to the stone is, perhaps, by means of a template made of cardboard, plastic material, or sheet metal, and for this purpose, a set of templates should be cut to cover the range of tool settings required. The sheet material can be marked-out with a protractor and then cut and, if necessary, filed to shape.

When a suitable protractor is not available for this purpose, the necessary dimensions can readily be calculated by the use of simple trigonometry. In Fig. 10 AB represents the surface of the stone, CB the line of the tool, and X the angle to be marked-out. The angle T remains a right-angle throughout.

Now, if we take a piece of sheet material with two sides formed at a right-angle to represent the angle T% and if we mark-off CB as, say, 4 in., then we have only to determine the length of AC to mark-out the angle X by joining the points A and B, and so complete the template.

In trigonometry the ratio of the length of AC to CB AC

expressed as ^, represents the tangent of the angle X, CB

which we will assume to be 30 deg.

Reference to a set of tables will show that the tangent of an angle of 30 deg. is equal to 0.577. If, therefore, CB = 4 in.

= 2.308 in. or 2 5/16 in. will be sufficiently accurate for our purpose. With a base CB of 4 in. the length of the perpendicular AC will be as shown in the following table.







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Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

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