Emery grinding machinery: a text book of workshop practice in general tool grinding, and the design, construction, and application of the machines employed by Hodgson Richard Broom

Author:Hodgson, Richard Broom
Language: eng
Format: epub
Tags: Grinding and polishing, Emery-wheels
Publisher: London, C. Griffin & company, limited
Published: 1903-03-25T05:00:00+00:00

Fig. 79. Ej^amples of Cutter Grinding.

In the case of any cutter, reamer, or tap, when it is necessary to keep their diameter correct to standard size, then the sharpening must be done by applying the emery wheel to the " top-rake" side (see fig. 79, at E and I), and on no account should the " clearance " side of the cutting angle be touched by the emery wheel.

In the designing of metal-slitting saws, which are really one form of cutter, there are two important points often overlooked by well known makers. The points are — No, 1, the cutting angle; No. 2, the clearance: these govern to a great extent the strength of the teeth, as will be readily seen by a study of figs. 80 and 81. The ordinary metal-slitting saw is seen at fig. 80, in which case it will be noticed

that the " (o»-rafte" side of the „. „ ,. „,. . „

■'^ , .Fig. 80. Ordinary Slitting Saw.

tooth 18 part of a line running

nearly stra^ht from the circumference of the cutter to the centre

of the hole in the cutter. The cutting angle is then formed by a

line running from the top of one toOth to the base of the next tooth;

the tooth terminates in a sharp point like a turning-lathe tool;

but though this form of tooth is used extensively for slitting

metal, it is really more suitable for sawing wood. The author

can instance a case where some hundreds of these metal-slitting

saws were in daily operation. The special points of interest that

were noted during the everyday working of these saws were

as follows:—First, there being " no top-rake" and too much

" clearance," it became necessary to apply a very slow rate of

feed, because the teeth had a great tendency to rip or rag the

metal instead of cutting freely. Second, the teeth having a

cutting angle similar to a wood saw, they were not of sufficient strength for cutting or sawing metal, consequently the teeth often snapped ofif; this tendency to break was further increased by the ripping or ragging action in cutting. Hence it was a common experience to see a dozen or more saws thrown away during one day's working. Considering the heavy cost of these saws, the loss became a serious item. The saws were sharpened in the manner shown in fig. 79, at 0. The continual losses in this respect led to the adoption of a special form of saw tooth (see fig. 79, at N). It is therefore surprising to see so many saws now in use having their teeth of similar shape to those in fig. 80. Let us compare the two shapes by considering them in the light of a metal lathe turning tool. To do this we will refer to fig. 81. S S is a steel shaft 2 inches in diameter ; this shaft is being turned by an ordinary round-nosed turning tool, which has a suitable top-rake T Eg of 10" and a clearance angle of 10°, thereby forming a cutting angle of 70°; this turning tool will be found to give good results when operating on steel.

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