276 APPLIED SCIENCE 



the reamer. The number of flutes is generally made odd 

 in order that there will always be two teeth opposite one 

 tooth. These two teeth stay or hold the tool better so that 

 it does not tend to wobble or chatter as much as it would 

 with but one tooth opposite one tooth. It is easier, how- 

 ever, to caliper (measure) a reamer with an even number 

 of flutes, having one tooth exactly opposite another on the 

 diameter. With reamers having a large number of teeth, 

 the odd or even feature is not of so much consequence. 

 Shell and rose reamers may be given the same number of 

 flutes and have their cutting edge formed in the same 

 manner as solid reamers. 



315. Emery Cloth. The art of finishing or polishing 

 wood and metal is very old. Originally it was done by tak- 

 ing the dried skins of sharks and rubbing the material. 

 Later sandpaper and emery cloth were invented. As 

 nearly as can be ascertained, emery cloth and sandpaper 

 came into use about two hundred and fifty years ago. The 

 process of manufacturing was then very primitive, consisting 

 of coating the backing with glue, covering it liberally with 

 the desired abrasive, shaking off the superfluous material, 

 and hanging the sheet up to dry. The steady march of 

 progress, however, has brought about wonderful improve- 

 ments in the manufacture of abrasive papers and cloths. 

 At the present time emery cloth is made from Turkish emery 

 of different grades. Turkish emery is a hard black and brown 

 stone found in Turkey and brought to this country for use 

 in machine shops. Its quality, for hardness and durability 

 in mechanical work, has never been excelled in any stone yet 

 found. The cloth made is of various grades of coarseness. 

 The numbers representing the grades of emery run from 8 



