Fig. 2199.
An instrument, patented by R. Drummond, for finding the depth of cutting edge and also for finding the curves, is shown in [Figs. 2198] and [2199]. It consists essentially of a bar g bent at a right angle, thus making two arms. Upon one arm is a slide w (best seen in [Fig. 2199]) secured by a set-screw b, and having at a a pivot to carry a second bar h, which is slotted throughout its length to permit bar g to slide freely through it. Upon the other arm of g is a slide p secured by a set-screw c, and carrying a compass point e. The bar h carries an adjustable slide z secured by a set-screw d and carrying the compass point f.
Fig. 2200.
In using the instrument but three very simple operations are necessary. First, the two slides w and p are set to the numerals on the bar, which correspond to the size of the head on the moulding machine the cutter is to be used upon; thus in [Fig. 2199] they are shown set to numeral 2, as they would be for a 2-inch cutter head. The instrument is next opened, its two bars occupying the position shown in [Fig. 2199], and the two compass points are set to the height of the moulding or to any desired member of it, as the case may be. The bars are then opened out into the position shown in [Fig. 2200], and the compass points at once give the depth of cutter edge necessary to produce the required depth of moulding.
It will be noted that the pivot a represents the centre upon which the cutter revolves, and that while the face of the bar h corresponds to the line of moulding formation answering to line a a in [Fig. 2196], the face of bar g corresponds to the face c f of the cutter in [Fig. 2196]; hence the instrument simply represents a skeleton head and cutter, having motions corresponding to those of an actual cutter head and cutter.