If the head has T slots instead of bolt holes, the slots may be cut or filed out to effect the balance, care being taken to make the slot equal in distance from the edges of the cutter seat face.
The next essential in order to have a properly balanced cutter head is that the bolts and nuts all weigh alike, and that the bolts be of the same length. The bolts should be turned to an equal diameter of equal length and threaded for an equal distance along the body of the bolt, and the nuts should be of equal depth and all fit accurately to the same wrench, and the weight of the bolts and nuts when put together may then be equalized by reducing the heads of the heavy ones.
We now come to the balancing of the knives, which must be made of equal thickness and width throughout, with the slots for the bolts of equal widths and depths.
The knives require to be as accurately balanced as it is possible to make them, for otherwise they will cause the head to jar and vibrate violently, thus producing rough work. The knives weighed individually may be of the same weight, and yet the head may run out of balance by reason of one end of a knife being heavier than the other end.
Fig. 3173.
[Fig. 3173] represents a machine constructed by J. A. Graham & Co., for balancing planer knives, moulding knives, cap screws, and knives in rotary cutter heads of all kinds.
Let it be supposed that the knives are the same specific weight, but that there is an excess of weight at one end; when revolving on the head, a violent jarring or throwing will be caused by reason of the excess. The knives could be reduced to the same specific weight by the aid of common grocers’ scales, but the ends could not be made the same proportional weight as on such balance.
In the cut s s is the base of the scale; l, m the standards for the support of the scale beams b b and k k.