PLANING THE STRIPS 71 



be finished by filing; and it is very difficult to prevent 

 the wearing down of the mold even in the most care- 

 ful cross-filing. Such distortion of its originally 

 even surface produces hollow places in the sides of 

 the rod-strips, and consequently in the resultant rod- 

 joints, and to a more aggravated degree as each suc- 

 ceeding strip leaves the mold. Wooden molds are 

 further deficient in accuracy, as compared with steel 

 molds, because the edges and angles of a wooden 

 groove are less sharply defined than is possible with 

 steel. 



We will give sufficient details, however, of a com- 

 mon way of constructing wooden molds, both be- 

 cause we make a preliminary use of such a mold 

 which can thus serve us in the building of many rods 

 of entirely different dimensions and in order that 

 the reader may judge how much simpler and more 

 efficient is the process that the author personally uses 

 and commends. 



The triangles composing a hexagonal rod-section 

 are equilateral triangles; such triangles have angles 

 of 60 degrees, and three of them make just half of 

 the section, comprising 180 degrees, as there are 360 

 degrees in a circle. It therefore is apparent that we 

 must plane down our strips flush with the face of a 

 groove having an angle of 60 degrees. 



Only the split faces of each strip are cut down, 

 and these by bringing them uppermost in alternation. 

 The rind or enamel surface lies always against one 



