2/8 TOWERS AND TAXfCS FOR WATER-WORKS. 







punches or dies, properly spaced. The area of the rivet-hole 

 should be about Vic inch greater than that of the rivet pro- 

 posed to be used. 



Plates having a thickness between and -J inches should 

 be punched Vie nlcn I GSS > an( J reamed out; while plates over 

 that thickness should be drilled from the solid sheet. 



While it has been shown that for tank work, plates, re- 

 gardless of thickness, can be connected in a more mechanical 

 fashion by requiring the horizontal seams to be a lap and 

 the vertical joints a strap connection, for reasons of econ- 

 omy, the lap-joint is used and will probably continue tin use 

 for connecting all plates, for both horizontal and vertical 

 seams, where the thickness of the plates are less than \ inch, 

 and possibly a thickness of l:J /i6 nicn should be considered 

 as the maximum permissible thickness for the use of a lap- 

 joint. In order to make the lap-connection, a corner of the 

 plate has to be heated and drawn out to make the joint where 

 three plates come together. This drawing out after heating" 

 is called " scarring," and is objectionable, both on account of 

 the unmechanical joint produced and as well as from the fact 

 that this reheating and working of the steel reduces its 

 strength, as has been explained in the chapter on the Phys- 

 ical and Chemical Properties of Steel. 



When, from reasons of economy or other necessity, this 

 reheating is permitted, that it may be as little objectionable 

 as possible, it is recommended by authorities that the tem- 

 perature of the metal, and which permits working, shall 

 range between a heat which will ignite hard wood and the 

 boiling temperature of water. In flanging or other bending. 

 it is sometimes necessary to work over the metal in this way, 

 but for bending sheets and angles to radius for tank work. 

 heating is not necessary and should not be allowed, it being 

 entirely possible to bend the metal to the required shape 



