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CMfTAO Fig> 33>

Should the tool be found not to cut freely, slight relief may be given behind the cutting edge by using an oilstone slip, but if this is carried to excess the tool will tend to chatter.

Reamers. The end portion of a parallel straight-fluted reamer is shown in Fig, 34, and a drawing depicting the tooth form in section is given in Fig. 35a.

Hand reamers are usually tapered towards the point for a short distance to give a lead into the hole at the start of the reaming operation. During manufacture, and after the flutes have been milled in the tool blank, the reamer is hardened and tempered before the final grinding to size over the crests of the teeth.

This process is carried out with extreme accuracy in

a grinding machine specially equipped for the purpose, and its repetition is usually beyond the resources of the small workshop. Moreover, were the crests of the teeth reground in this way, the diameter of the tool would be reduced, and it would not then cut to its full nominal size.

Fig. 35b illustrates the result of extreme wear, and it will be seen that the sharp crests forming the cutting edges have been worn away to form flat surfaces that will merely rub, and not cut, the internal surface of the hole into which the reamer has been introduced.

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