Ornamental lathe components by Holtzapffel.

Ornamental lathe components by Holtzapffel.

This is a foot lathe made by Holtzapffel & Co for ornamental turning. The fast headstock has a parallel mandrel with long bearings, but for most classes of work the mandrel is pushed back until a cone on it thrusts against the front bearing, where it is retained in position by a long collar fitting over the back end and fixed to it. The face of the cone pulley is perforated with circles of holes to act as a division plate for setting out or spacing work. To the small end of the step pulley is attached a disc with a thick rim pierced with 72 large holes, in which pins can be inserted to limit the rotation of the mandrel by coming into contact with an adjustable stop; this is for the purpose of producing segmental ornament, the mandrel being turned through the required angle by hand or by a disconnecting tangent screw and worm wheel, which may also be used for dividing. For work between centres a poppet head or loose headstock is provided; there is also a collar plate to give circumferential support to long objects when being bored from an overhanging end.

A slide-rest is fitted having two slides in directions at right angles to each other. The lower slide with V-edges is very long and the screw is provided with a handle and micrometer wheel at one end, whilst its upper surface is graduated in inches and tenths. The slide is mounted on a swivel mounting with a lock nut and may be raised or lowered and set at any desired angle to the bed. The upper slide also has a feed screw and small micrometer wheel and a stop for ensuring constant depth of cut. The tool is held in a slot in the top slide by two vertical screws which pass through blocks held in the slot by flanges.

The oval or elliptic chuck in its present form was patented in 1764 by James Williamson and Joseph Spackman, but chucks identical in principle, although slightly different in construction, were in use in 1700.

The chuck shown consists of a back plate screwed on the mandrel nose, and having on its face a front plate carrying the work and sliding between V-guides. The front plate is controlled by means of studs passing through slots in the back plate, and having flat cross-pieces, which are in contact with the exterior of a ring projecting from a frame, secured to the face of the headstock at the level of the centres by pointed screws, and capable of horizontal adjustment to obtain any required eccentricity. The work thus receives an oscillating motion across the mandrel, which causes it to recede from the tool twice per revolution, in such a manner that a stationary tool cuts on the work in any position true ellipses, the limit being a straight line when the point of the tool is at the centre of the mandrel. These curves have a constant difference between their major and minor axes, equal to twice the eccentricity of the guide ring: the strip between any two ellipses is consequently not exactly uniform in width. A hand tool can be used on the rest, but owing to the importance of constancy of height such work is simplified by the use of a slide-rest.

For cutting the short screws chiefly required for fastening together the parts of ornamental work, the mandrel is traversed and the tool held stationary. For this purpose the collar on the back end of the mandrel is replaced by one of a series of short guide screws; below this and attached to the headstock is a plate having around its edge segments cut with threads corresponding with the guide screws, and this plate is mounted on an eccentric pin, by which it can be put in and out of gear. When screws or helices of greater length than the guide screws or of other pitches are required, the longitudinal screw of the slide-rest is connected with the mandrel by change wheels. The equipment with this lathe includes an oval chuck and spiral apparatus by Holtzapffel, a slide-rest by J. H. Evans, and a universal cutting frame.