PATTERN MAKING 



21 



The Core-Box Plane. The core-box plane, shown in Fig. 35, 

 while not indispensable, will be found to be a very rapid working 

 and useful tool for making semicircular core boxes up to 2| inches 

 in diameter. By using the 

 extension sides, one of 

 which is shown in the illus- 

 tration, and two pairs of 

 which are always furnished, 

 this tool will work accu- 

 rately a concave semicircle 

 up to 10 inches in diameter. 



The core-box plane is 

 constructed upon the prin- 

 ciple that if the sides of a 

 right angle lie upon the 



extremities of a diameter of Fig. 35. 



a circle, the vertex of the right angle will lie upon the circum- 

 ference of the circle. This is illustrated in Fig. 36, from which it 

 will be seen that if the block of wood has been worked to a perfect 

 semicircle, and the edges of the blades of a try-square or right- 

 angled triangle touch the semicircular curve at its extremities, 







the right angle or corner will touch the arc at some point, as l,eor 

 A, the angles abc, def, and ghi all being right angles. 



To this kind of plane the objection is often made that it 

 abrades and wears off the corners of the semicircle as it is being 

 worked out. This, however, can be practically avoided if the 

 following instructions are followed: 



