2O SCIENCE OF THRESHING. 



relieving the separating devices from some of the 

 work of removing the grain from the straw. Con- 

 cave teeth serve the further purpose of retarding the 

 grain while it is being acted upon by the cylinder 

 teeth. The greater the number of teeth the more the 

 straw will be retarded and acted upon by the cylinder. 

 Separators are usually constructed to use concaves of 

 several sections, each section being provided with two 

 or three rows of teeth. In adjusting the position of 

 the concave relative to the cylinder, it must be borne 

 in mind that some grain requires very positive action 

 on the part of the cylinder teeth to dislodge the grain 

 from the head; accordingly, when threshing grain 

 of that sort it is well to set the concave close and 

 employ all the sections. In grain that is less stub- 

 born, a section of the concave may be removed and 

 replaced by one without teeth with good results. 



There should be stops provided to prevent the 

 concave from being raised too high so as to give a 

 proper clearance. It is better practice to set the 

 concave up close and use few teeth rather than to 

 lower the concave and employ a greater number. 

 The latter plan leaves a space below the points of the 

 cylinder teeth which permits the straw and whole 

 heads to pass without being acted upon. If the 

 straw be very dry and brittle and inclined to break up 

 badly, it lies more loosely and can therefore be given 

 a considerable more space by letting the concave 

 down. 



Some types of concaves are adjustable, both at 



