When the cutters require to stand far out from the head, the bar will work more steadily if the cutters, instead of standing radially in the head, are placed as in [Fig. 1134], so that they will be pulled rather than pushed to their cut.
Fig. 1135.
An excellent form of boring bar fixed head, employed by Messrs. Wm. Sellers and Co. on their horizontal cylinder boring machine, is shown in [Fig. 1135]. The boring head is split at a, so that by means of the bolt b it may be gripped firmly to the bar d, or readily loosened and slid along it. The head is provided with cutters c (of which there are four in the latest design of bar), fitting into the radial slots e. These cutters are secured to the head by the clamps and nuts at g.
Fig. 1136.
[Fig. 1136] represents a boring bar, with a sliding head fed by a feed screw running along the bar, and having at its end a pinion that meshes upon a gear or pinion upon the dead centre of the lathe.