Fig. 71.

Bar And Bed Lathes Continued 40062

Fig. 72.

Bar And Bed Lathes Continued 40063

Fig. 73.

Bar And Bed Lathes Continued 40064

Fig. 74.

Bar And Bed Lathes Continued 40065

Fig. 75.

Bar And Bed Lathes Continued 40066

Fig. 76.

Bar And Bed Lathes Continued 40067

The bearers of large and long lathes are of greatly increased substance, proportioned to their increased dimensions, and are usually of the section fig. 75; the external, angular sides are required for guiding the traverse of the slide rest, while the projecting ribs along the lower edges to increase the stiffness are very frequent. The angular grooves at the sides of fig. 76, are adopted to avoid excessive width upon the face of the bearers of slide lathes, in cases where comparatively large internal space is required for the guide screw and clutch box.

The bar lathe fig. 67, has been occasionally constructed with the bar movable in the head, to adapt a lathe of small dimensions to turn work of increased length and diameter; in the manner shown by fig. 77. The lathe head has a triangular mortise in the direction of its length, shown by the dotted lines, this receives the bar, which is also supported by two pedestals attached to the lathe frame. The left hand pedestal having a horizontal traverse in a slot in the table of the lathe frame, so far as the dotted position. For work within the ordinary capacity of the lathe, the bar is supported within the head and by its two pedestals; for that of increased diameter, it is withdrawn from the lathe head and together with the movable pedestal, is shifted so far to the right as required by the thickness of the work. The tool rest, is carried on a short portion of the bar left projecting beyond the movable pedestal, and the work may be of any diameter, not exceeding the radius from the top of the bench to the lathe center.

Fig. 77.

Bar And Bed Lathes Continued 40068

For long rods, the movable pedestal and the bar carrying the popit head, are shifted still further to the right, as shown by the dotted lines; but as the tool rest can only travel the length of the bar, the work has to be turned end for end, to bring each half in succession within range of the tools; the half under operation being that most distant from the lathe head, which also suffers the most vibration. The popit head also so considerably overhangs the end pedestal, that it requires to be supported by a temporary prop or strut of wood from beneath it to the floor. The already small stability of the bar lathe is further considerably diminished in this arrangement, which apparently very convenient is not really satisfactory; while this form of bar lathe, also presents a strong temptation, to habitually use the apparatus for works that are too large for its fair capabilities and strength. Long and slender works, such as are indicated by the dotted lines, also require some guide or stay to prevent them springing away from the tool. Somewhat analogous arrangements, for turning works that are of greater radius or of greater length than the normal capacity of the foot lathe will admit, are made in the ordinary bed lathe, the structure of which is much more favorable to the purpose; these and some varieties of the guides and backstays are mentioned in another chapter.

Increased capacity for diameter is frequently attained by making the bearers in two lengths, one only sufficiently long for the lathe head, the other as long as required, fixed with a small interval between their ends, both being placed in one line. Such arrangements are occasionally required by the wood turner, and more frequently by the engineer; by the former, usually for specific purposes, such as the manufacture of turned picture frames or other works of slight thickness. The oval frame turner frequently completely separates the two parts, placing the shorter portion of the bearer carrying the lathe head, at right angles to the longer and at about the center of its length; an arrangement very convenient for his purpose, obtaining a solid support for the hand rest, close to the surface of the work at all distances from the axis of the lathe. The height of the center of the foot lathe is most satisfactorily increased by the temporary employment of lifting pieces, hereafter mentioned, and this expedient not only meets the requirements of most of the occasional works, larger than the ordinary capacity of the foot lathe, for which the power of the latter is sufficient ; but, it has the great additional advantage of leaving the length and the face of the bearers intact.

The break or gap lathes used by the engineer and usually driven by power, are principally intended for works of large diameter but of comparatively small thickness, and are employed for such purposes as that of boring the centers and turning the edges of wheels, or centers and bosses at the extremities of long pieces. In the smaller of these gap lathes, the bearers are cast in one piece, with a vertical bend or crank in front of the lathe head, fig. 78, the gap being closed by a loose filling piece when the lathe is employed for ordinary work. This formation is not entirely satisfactory, the form of the bearers being less able to resist, while liable to increased torsion; the uprights and the bearers have therefore to be constructed of greatly increased weight and strength, for the lathe to produce a smooth well turned surface on the work.

72 engineers' break lathe bearers.

Fig. 78.

Bar And Bed Lathes Continued 40069

The larger break lathes of the engineer are far more favorably constructed in all respects, the tall standards are absent, and the two portions of the bearers are bolted down exactly in a line on stone work and low iron pedestals, or else upon a heavy foundation of cast iron. When employed for work within the capacity of the height of center of the lathe head, the headstock sometimes stands over the gap and is bolted down to both portions of the bed; or, a movable short length is used to fill the gap for the time; or else, the two portions of the bearers have a power of longitudinal traverse and can be made to approach and join each other; the headstock in the two latter arrangements standing always on its own short piece. The bearers are also sometimes cast as one piece in the form of a cross, with the entire horizontal surface at one level; the two arms of the cross are close in front of the lathe head, and are hollowed as a trough to receive the work, the cross arm being also employed to carry the slide rest for turning surfaces.