Chap. XX. Of the Drill-Boxes. 325 



as is (hewn by the curve Line b d. We may enlarge 

 the Capacity of this Notch, by taking off the Con- 

 vexity of its Bottom, as in the Bottom of the Notch 

 {hewn by the Line e f\ and if we would increafe it 

 more, we make it concave, as g h. 



But of whatever Sort or Dimenfions one Notch 

 is made, all the reft mould be the fame exactly ; and 

 confequently, the Interfaces (or Intervals) between 

 Notch and Notch, of which the Line / c, being an 

 Arch of the Circle, is the Breadth, muft be equal (a), 

 and cannot be otherwife, if the Notches are all equal 

 and equidiftant, as they appear in the adjoining Fig. 5. 

 which is a Section like the former, and fhews Six In- 

 tervals, with their Six Notches, of the Size wherewith 

 we drill St. Foin with high Wheels • but when we 

 would drill very thin, it is better to have but Four or 

 Five Notches inftead of Six. 



Fig. 6. {hews a Notch of the Spindle, a b is the 

 upper Edge of the Side of the Notch, being always 

 an acute folid Angle, c d is the Edge of its Bottom, 

 being always an obtufe Angle, e f is the Angle 

 made by the Side and Bottom, and is always fhorter 

 than the aforefaid Two Edges, by reafon of the 

 Obliquity of the Two Ends -, this Angle is never 

 obtufe, except when the Bottom of the Notch is con- 

 cave. Thefe Three Lines muft be parallel to the Axis 

 of the Spindle, 



Fig. 7. is one End of the afore-defcribed Notch 5 

 the Line a b being joined to the Line / d of Fig. 6* 



Depth may. The concave Notch, if it were as broad as the 

 convex may be, would make the Interlace, that is before it, 

 liable to be broken out, and fo Two Notches would become One; 

 but the Convexity of the other fupports the Interface like an 

 Arch, and for that Reafon may be made to reach almoll quite to 

 the Notch that is before it, without that Danger. 



(a) But thefe cannot be equal, unlefs the Notches are ail of 

 equal Breadth, and equidiftant from one another; and if they are 

 Oihcrwife, the Seed will not be equally delivered to the Ground. 

 Y3 and 



