. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . ite with instance, brass invariably demands a negative one attempts the slightest operation upon brass witha tool having a positive rake, the tool is almost sure tobite into the work, spoiling it and perhaps break the tool,Be sure to have the top surface of the tool ground so thatit slopes downward toward the work when cutting , on the other hand, demands a decided positiverake. It is not necessary to regrind the entire
. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . ite with instance, brass invariably demands a negative one attempts the slightest operation upon brass witha tool having a positive rake, the tool is almost sure tobite into the work, spoiling it and perhaps break the tool,Be sure to have the top surface of the tool ground so thatit slopes downward toward the work when cutting , on the other hand, demands a decided positiverake. It is not necessary to regrind the entire cutting sur-face of the tool when changing from one to the the tool has normally a positive rake for steel, oneneeds merely to take the tip of this rake off so that just Lathes and Lathe Work 35 the cutting edge lias a negative rake when brass is tobe cut. In turning from a casting,- take a cut sufficiently deepthe first time to get quite beneath the scale or hard cruston the casting. Be sure this crust is cut right through,as, if it scrapes the tool at all, the cutting power of thelatter will be destroyed and it must be Facing Endof Shaft- Po SI fiveRake - Steel Nega+fveRake- Brass Fig. 14—A. Using a left-hand side tool. B. Using a right-hand side A right-hand bent tool. D. A right-hand diamond point tool. diamoiid point tool. F. A round nose tool. G. A cutting-off or parting tool. H. Bent threading tool. I. Roughing tool. tool. K. Facing the end of a shaft with a right-hand facingtool. L. A tool ground with a positive rake for cutting steel. M. Atool ground with a negative rake for cutting brass. 36 Model Engineering The clearance of a tool is the separation or, as itsname implies, the clearance between the body or support-ing portion of the tool and the work being cnt. The illus-tration showing the various angles for cutting tools illus-trates this clearly. All tools must have clearance toprevent the unused portion of the t
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