134 



Table 87. Wood for Professional and Scientific Instruments, year ending 



June, 1912. 



PULLEYS AND CONVEYORS. 



The commodities grouped in this industry are tackle blocks, belt pulleys, 

 conveyors, and clutches, and thirteen kinds of wood are used for making 

 them. Metal has to a large extent replaced wood in this line of manufacture, 

 but studies similar to this in various states have shown that a considerable 

 quantity of wood is still demanded for making them. For belt pulley rims the 

 manufacturers in Pennsylvania call for birch, basswood, yellow poplar, cucum- 

 ber, cottonwood, and butternut, and for the center arms, red oak, white oak, 

 sugar maple, ash, and beech. 



Tackle block material must be dense, hard, strong, tough, and most diffi- 

 cult to split. White ash, sugar maple, and a small amount of black gum are 

 the woods reported in use in Pennsylvania though in other states elm is 

 frequently used. Pulley blocks are of many types and sizes in order to meet 

 a variety of uses. For example, those required on vessels, in building con- 

 struction, in mines, on derricks and hoists by house painters, masons, car- 

 penters, etc., range from a snatch block to the multiple pulley blocks. The 

 latter is usually of the shoulder block type and designed for one or more 

 sheaves. It is sometimes chambered out to receive a wheel in each compart- 

 ment while at other times two or more wheels are placed side by side in a sec- 

 tion. The old time block maker did much of the work by hand, but the im- 

 proved machinery in recent years does the work with greater accuracy and 

 in much less time. The lumber is ripped Into dimensions the width of the 

 block and the reciprocating saw then cuts the dimensions into shape, when 

 they are passed on to be mortised. Often the wheel slats are cut by machinery 

 and then the blocks are ready for the sheaves. 



A small part of this industry consists In the manufacture of conveyors such 

 as are used in factory elevators and warehouses to carry merchandise and 

 grain. These require only a limited amount of wood for small partg and 

 white oak and sugar maple are the species reported. 



