398 APPLIED SCIENCE 



451. Template. A template is a temporary pattern 

 guide, or model by which work is marked out, or by which 

 its accuracy is checked. Working to a template requires 

 accuracy on the part of the operator, as the forging is gener- 

 ally finished by him, except where it is to be spotted or 

 finished in the machine shop. 



452. Shrunk Fits. Blacksmiths and metal-workers usu- 

 ally fasten one piece of metal around another by shrinking the 

 first onto the second. This process, known as a shrink, is 

 applied in attaching various kinds of bands, collars to shafts, 

 in putting tires on locomotive wheels, and in shrinking steel 

 gear rings to steel centers. The piece of metal to be shrunk 

 on must be slightly smaller than the outside diameter of the 

 part to which it is to be applied. It is heated and expanded 

 until it can be slipped into place, so that when it cools it will 

 cling to the part with sufficient strength to hold it in place 

 during service. 



453. Allowance for Shrunk Fits. It is the practice in 

 shrunk fits to allow -j-uW of an inch for each inch in diameter. 



To illustrate: A locomotive tire 68 in. in diameter should be 

 turned 68 X iVmr in-, or f-J-jf-o- in., smaller than 68 in. Expressed 

 in a formula this is: 



A = .001 X D = 1T ? in. 

 Where A is allowance in inches, and D is diameter in inches. 



454. Forced Fits. Sometimes parts are assembled in a 

 cylindrical or slightly tapered form, and fitted under pressure. 

 The method is called a forced fitting. An allowance of .001 

 or .002 is made for each inch in diameter. 



