38 



Every pattern shop should have at least one do/en each of 

 three or fonr different sizes of hand-screws or clamps similar to 

 that shown in Fig. 70. These arc 1 adjustable 

 through wide ranges. They are used for 

 clamping together the material that is being 

 glued up to form the different parts of a 

 pattern, and are convenient also for many 

 other purposes. The all-iron C clamp, shown 

 in Fig. 80, is sometimes useful in positions 

 that are hard to reach with a hand-screw. 

 The method of adjusting and of using the 

 hand-screw will be fully explained later. 



RULES. 



For all ordinary measurements, a 2-foot, 

 folding standard rule, Fig. 81, will be suffi- 

 cient, but this rule must not be used for laying 

 out or for working patterns, or any part of a 

 pattern or core box, to the required dimen- 

 sions. For all such piirposes a shrinkage 

 rule must be used. The reasons are that 

 when a mould made from the wooden pattern 

 in the sand is rilled with molten metal, its 

 temperature is very high, and as it cools and 

 solidifies it contracts. Accordingly, to com- 

 pensate for this, the pattern maker must add 

 to the size of the pattern. In order that this 

 may be done, and exact relations nevertheless 

 be maintained for all dimensions, a shrinkage 

 rule is used. This rule is marked off exactly 

 like an ordinary rule; but if the two are com- 

 pared, the shrinkage rule will be found to be 

 about inch longer than the other for each 

 foot of length . 



The contraction or shrinkage of different 

 Fig. 78. metals in the moulds varies greatly, that for 



cast iron being, as above stated, inch to each foot. For 

 brass, however,- the shrinkage is !% inch to the foot; and for 



