CHAPTER XXIII.

=EMERY WHEELS AND GRINDING MACHINERY.=

=Grinding Operations=; Classification of 38 The qualifications of emery wheels 38 Cements used in the manufacture of emery wheels 38 Grades of coarseness and fineness of emery wheels 38 Grades of wheels and the work they are suitable for 39 Speeds of emery wheels 39 Balancing emery wheels 39 =Emery Grinding Machines= 40 The Sellers drill grinding machine 41 The construction of the drill holding chuck 41 Varying the drill position to suit the diameter of the drill, and thus maintain equal conditions for all diameters of drills 41 Errors of construction in ordinary drill grinding machines 41 The construction whereby the Sellers machine maintains an equal degree of clearance from end to end of the cutting edge upon all sizes of drills 41, 42, 43, 44 The Sellers attachment for thinning the points of large twist drills 44 The front rake of twist drills 44 Emery grinder for true surfaces 45 For engine guide bars 45 For car axle boxes 45 Emery grinder with traversing emery wheel 46 For rough work 46 For planing machine knives or cutters 46 Emery wheel swing frame for dressing large castings, &c. 46 Emery belt grinding machine 47 Presenting emery wheels to the work, or the work to the wheels 47 Annular emery wheels 48 Recessed emery wheel 48 The wear of emery wheels 48 =Polishing Wheels= 49 to 51 The construction of 49 Lapping the leather on 49 Method of keeping them true 50 Charging with emery 50 The speed of 50 Polishing materials for 50 Brush wheels for polishing 50 Speed of brush wheels 50 Polishing materials for brush wheels for brass work 50 Solid leather wheels 51 Rag polishing wheels 51 Polishing materials for rag wheels 51 Polishing device for engravers' steel plates 51 =Grindstones= and Tool Grinding 51 The various kinds of 51 Suitable for wood working tools 52 Suitable for saws or iron plates 52 The speeds of 52 The changes of pulley diameter necessary as the diameter of the stone decreases in order to maintain a nearly uniform circumferential speed of grindstone 52 Arrangement of, for saw plates 52 Hacking 53 Device for truing 53 Automatic traversing device for 53 Considerations that determine the position in which the work should be applied to 53 =Oil-stones=, the various kinds of 54 Truing oil-stones 54 Removing the feather edge left by 54 Oil-stoning edge tools 54