The lathe in which the work alone revolved between fixed center points, received its greatest improvement in the introduction of the mandrel, by which arrangement the work is attached to the end of a spindle, the two revolving together. The old French writers, styled lathes provided with mandrels, "tours en l'air," evidently from the freedom and independence of the work; the whole of which, except the portion by which it is attached to the mandrel, being accessible. The adoption of the mandrel opened the way to the very considerable development in chucks and other lathe apparatus, that has since been continuously effected.

The revolving mandrel would appear to have arisen as an extension of the arrangement employed for turning hollow objects; the germ being found in the spring bow lathe fig. 22. The gem engraver drawn by Schopper, 1568, uses a mandrel lathe, and Felibien pages 379, 380, thus describes the use of the mandrel in turning, he says, "For turning hollow work. "such as vases, one of the center heads is removed, and a "thin wood or iron collar with a round hole is substituted. "The collar also serves to support mandrels or arbors, pieces "of wood made in the form of pulleys or otherwise, against "which are fastened, either by cement, or the points of nails "or screws, or in any other manner, certain works that can-"not be turned between two points, such as boxes and many "other things."

The wooden mandrel was before long replaced by a light rod of iron, having a center point at the one end and formed into a screw at the other; the latter being introduced as a more convenient attachment for the work than the nails or cement. The iron mandrel, fig. 61, copied from Bergeron, was surrounded by a tube or casing of wood, turned to two or more diameters separated by enlargements of the material, the first to vary the speed, and the last to guide the string of the pole or bow; the screw end running in a hole in the guide plate fig. 22. Subsequently the mandrel was provided with one or two rings or flanges of iron and was placed to run between divided wooden collars, joined like a pair of compasses to permit occasional separation for its removal.

Fig. 61.

Lathes With Revolving Mandrels Section I Mandrels  40054

The iron mandrel was but a short time in use before it was also employed for cutting screws mechanically; the majority of the early mandrels taking that form. Plumier describes an iron mandrel which is of interest as exhibiting the divided wooden collars, and also as showing the first application of the traversing motion, together with the method he employed for cutting the guide screws.

The following is condensed from our author's account of the process. He directs the mandrel to be forged, annealed and very carefully centered, and then to be turned true in a strong center lathe with heads of small elevation. The mandrel is then to be supported after the manner shown by fig. 62, while the hole that is ultimately to receive the chucks is being drilled. He condemns the use of die stocks, for the formation of the screw guides, to be next cut upon the mandrel, from the risk of bending that, or of cutting these screws out of truth, and recommends either of the following as superior methods.

Fig. (52.

Lathes With Revolving Mandrels Section I Mandrels  40055

By the first, an angular slip of paper is to be very accurately coiled around and then cemented upon the mandrel; and the margin forming the line of the screw, is to be carefully followed by the edge of a thick knife, to cut through the paper and mark a fine screw line on the iron; which line is to be enlarged with a delicate fine edged file, and then by one of triangular section. The mandrel so far prepared by hand is then to be placed between centers and the screw completed during its revolution, with the file or with a screw tool filed by hand to the same intervals or thread. A very similar method of originating screws was still sometimes employed so late as about the commencement of this century, particulars of which are given page 579, Vol. II.

The second method described and preferred by le pere Plumier is shown by fig. 62. The hole drilled for the internal screw for the reception of the chucks, is temporarily used to hold the shank of a tap, of the same thread as the screw guide required, the tap being fixed in the mandrel by tin solder, so that the two may be exactly in one line to possess a common axis. They are then supported in jointed semi-cylindrical wooden collars, the tap being allowed to cut a thread in the one pair, to serve as a guide, and to cause the traverse of the mandrel during its rotation. The pointed tool used to cut the external screw guides upon the mandrel, is held on the rest by the hand, but to retain it stationary two pins are inserted or a notch is cut in the rest the width of the tool, as represented. The internal screw for the chucks was obtained in a similar manner being copied from one of the external screws cut upon the mandrel.

The general form of the mandrel lathe, so far as the wooden bench and headstocks were concerned, was for a considerable time modelled upon that of its predecessor the pole lathe; the mandrel head alone was altered, being duplicated and modified to receive divided collars of lead or tin, cast in dovetail recesses, these collars being much like the divided metal bearings now generally employed for machinery. The plain mandrel was forged entirely of iron with a cylindrical neck or pivot at either end, that in front having a projection or shoulder for the chucks to screw against; the central portion was forged square and slightly taper for the wooden pulley. After the necks had been turned true between the heads of a center lathe; the mandrel was placed in the perpendicular recesses of its wooden pedestal, still supported by the points of the center or pole lathe, and melted lead or tin was poured in to fill the space between the wood and the mandrel, to form the lower halves of the collars. All the parts were then dismounted and the half collars filed down to the diameter, after which the half collars and mandrel were replaced, to cast the remaining halves to form the entire bearings. These were completed by cross pieces above, attached to the heads, having central pressure screws to retain the two halves of the collars in contact, and to supply a compensation for wear. In casting the collars, the mandrel required warming nearly to the temperature of the metal, to avoid chilling the latter before it had entirely filled the apertures; these also had to be effectually stopped to prevent the metal escaping, by plates of wood filed to the circle of the mandrel, tied on with wire and cemented with clay.