Fig. 202 shows the usual form of cutter arbor, in which A is the taper shank fitting the taper-reamed hole in the milling-machine spindle; B is the flattened portion or tang fitting in the cross-slot and preventing the arbor from turning; C is a nut used in withdrawing the arbor from the hole when it has been forced tightly into it; D is a collar formed upon the arbor, against which loose collars or the cutter itself are forced when placed upon the arbor at E and confined by the clamping nut F. The end G is finished as a journal or bearing for an outer support attached to or forming a part of the overhanging arm of the milling machine. In the outer end is drilled and reamed a center hole for a similar purpose.
Fig. 202. Ordinary Form of Cutter Arbor.
Cutters are prevented from turning upon the arbor in any one of four ways-namely, first, by a key in the keyway DE, Fig. 200; second, by being clamped between loose collars on the arbor; third, by being threaded and screwed on the arbor; and fourth, when the cutter is quite small and the work light, by a large-headed screw, slotted for the screwdriver, and tapped into the end of the arbor. In the latter case, the thread must be right- or left-handed, according to the direction of revolution, so that the torsional strain of the work will tend to keep the cutter screwed tightly against the shoulder.
Fig. 203. Screw-Slot Cutter.
Fig. 204. Slitting Saw.
Usually cutters are made right-handed; that is, if held so that the side which goes against the collar on the arbor is toward the eye, the cutter should turn in the same direction as the hands of a clock.
To locate the cutter in the proper position on the arbor to suit the work to be done, loose collars of various thicknesses are used on the arbor, placing as many on each
Fig. 205. Plain Milling Cutter.
Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts side of the cutter as are necessary to fill the space between the fixed collar D, Fig. 202, and the clamping nut F. The cutter and loose collars must have smooth, true, and parallel faces; otherwise the arbor will be sprung when the clamping nut is screwed up, and will not run true.