Referring now to the die A, it acts as a guide rather than as a cutting chaser, because it has virtually no clearance and cannot cut so freely as B and C; hence it offers a resistance to the moving of the bolt, or of the dies upon the bolt, in a lateral direction when the chaser teeth meet either a projection or a depression upon the work. The guide principle is, however, much more fully carried out in a design by Bodmer, which is shown in Fig. 300. Here there is but one cutting chaser C, the bush G being a guide let into a recess in the stock and secured thereon by a pin _p_. The chaser is set in a stock, D also let into a recess in the stock, and this recess, being circular, permits of stock D swinging. At S are two set-screws, which are employed to limit the amount of motion permitted to D. the handle E screws through D, and acts upon the edge of chaser C to put on the cut. The action of the tool is shown in Fig. 301, where it is shown upon a piece of work. Pulling the handle E causes D to swing in the stock, thus giving the chaser clearance, as shown. When the cut is carried down, a new cut may be put on by means of E, and on winding the stock in the opposite direction, D will swing in its seat, and cant or tilt the chaser in the opposite direction, giving it the necessary clearance to enable it to cut on the upward or back traverse. Another point of advantage is that the cutting edges are not rubbed by the work during the back stroke, and their sharpness is, therefore, greatly preserved. A die of this kind will produce work almost as true as the lathe, and, in the case of long, slender work, more true than the lathe; but it is obvious that, on account of the friction caused by the pressure of the work to the guide G, the tool will require more power to operate than the ordinary stock and die or the solid die.
In adjustable dies which require to take more than one cut along the bolt to produce a fully developed thread, there is always a certain amount of friction between the sides of the thread in the die and the grooves being cut, because the angle of the thread at the top of a thread is less than the angle at the bottom. Thus in Fig. 302 the pitch at the top of thread (at A, B) is the same as at the bottom (C, D). Now suppose that in Fig. 303 _a_ _b_ represents the axial line of a bolt, and _c_ _d_ a line at a right angle to _a_ _b_. The radius _e_ _f_ being equal to the circumference of the top of the thread, the pitch being represented by _b_; then _k_ represents the angle of the top of the thread to the axial line _a_ _b_. Now suppose that the radius _e_ _g_ represents the circumference at the bottom of the thread and to the pitch; then _l_ is the angle of the bottom of the thread to the axial line of the work, and the difference in angle between _k_ and _l_ is the difference in angle between the top and bottom of the thread in the dies and the thread to be cut on the work.