Do It with Tools and Machinery 



Below: An automatic 

 saw file in operation. 

 There is no guesswork. 

 Each tooth files to an 

 exact slope and length 



At left and below: 

 An electric etching 

 machine for factory- 

 use. It marks for 

 identification costly 

 steel milling cut- 

 ters, drills, etc. 



718 



