268 



farmers' and mechanics' journal. 



The annexed figure is a joint that would do without bolts, but is 

 is clear that (he strength would not be quite so great as half the 

 Fig. 58. 



z 



p 



strensith of an entire piece. The key or double wedges, at a, 

 should only be driven so as to bring the parts to their proper bear- 

 ing, as it would be better to omit it, than to drive so as to b, oduce 

 much constant strain on the joint. It is not necessary th:i» there 

 should be a key. except when bolts are to be added, and then it is 

 desirable to bring the Joints to a bearing before the bolts be put in. 

 The addition of bolts and straps makes this an excellent scarf. 



The following figure is a slight modification of the last described 

 scarf, where the keys are supposed to be of hard wood ; if of a 



Fig. 59. 



curled grain so much the better. In this form the scarf is easier 

 to execute, and equally as good as the last, when bolts are used. 



The next figure represents a scarf where the oblique joints in 

 the last examples are avoided, and the same degree of strength is 

 obtained ; at the same time it is very simple and easy to execute. 



Fig. 60. 



To determine the length of a scarf, in joining beams, it is neces- 

 sary to know the force that will cause the fibres of timber to slide 

 upon each other. The researches upon this subject have already 

 been laid before the reader in Chap. Vlll. Fart 1. To apply 

 them to our present object, let A B, in the succeeding figure, be 

 Fig. 61. 



'^r 



