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Petermann Automatic Lathes
- Swiss-Auto Type Lathes -
Detailed Operator's Handbooks, Parts Lists and catalogues are available for
most Petermann lathes. Email for details

Screw-head Slotting   P3 lathe   P25 Lathe
P4, P7, P10 and P16 Lathes

Petermann automatic lathes are a fine example of the Schweizer Landdrehautomat - or "Swiss-Auto" - an automatic lathe of a type also first build in Switzerland by other makers such makers as A.Bechler and Tornos. Unsurprisingly, all three were based in the little French-speaking town Moutier, an important centre of Swiss watch, clock and high-precision industry. Machines were also developed in Germany, by Strohm, Gauthier and Thiel, as well as in other European countries.
Originally of entirely mechanical operation, with (at first) not an electronic circuit in sight, the machines were designed especially for the mass production of very small parts - hence their close connection to the Swiss watch industry. Used extensively for turning watch pinion shafts, axles and screws and parts for a variety of timing mechanisms, fuses, chronometers and precision mechanical instruments, their versatility and adaptability ensured that they were adopted for all manner of production jobs for which normal capstan (screw-machine) types were unsuitable. Today, since small screwed and other tiny parts - connectors for electronic components for example - are in ever-increasing demand for micro-electronic components, the Swiss-Auto type sliding-head automatic has adapted well to computer control and the addition of 3-axis control and multiple tool heads. The Taiwanese and Japanese, in particular, have had great success in this specialist area. Watch the video.
Beautifully constructed, the pre-WW2 No. 0 was the smallest ever of the Petermann models and intended for material up to 4 mm (0.157") diameter in brass and 2.5 mm (0.098") in steel As their success increased, all makers brought out larger models - Petermann's range included the P3, P7, P10, P16 and P25 - with the largest machines able to handle rod up to 30 mm in diameter). There was never any doubt about which Petermann machine was which for, casting to the body of each was the maker's name and model designation. l.
All Swiss-Autos were arranged along similar lines with, depending upon the model, up to six independent tool holders arranged radially on a cutter frame fixed in front of the (right-hand positioned) headstock nose. Each tool-holder was arranged to slide, its action triggered by a rocker arm connected (via a series of linkages) to a rotating cam. For round components only finely ground bar stock could be used, the job being either very short and so requiring no outboard support, or long enough to pass through one of several kinds of bushed support that held the work both accurately and securely against deflection. The longitudinal feed was obtained by sliding the whole headstock along the bed, at various rates and timings, also under cam control. By combining headstock and tool movements, cam shapes, cam timing and with various types of cutting and forming tools (and by mounting accessories) the lathes could perform miracles of miniature production engineering. When producing tiny parts, an important point was the very precise adjustment of the cutting-tool holders - and in this the setter was, originally, a highly-paid king. Originally the best results could only be obtained by long experience and trial-and-error-methods but, with the introduction of Petermann's "micro-differential" apparatus, where a micrometer was mounted on the end of each toolholder, the task became greatly simplified. The first setting took accuracy to within 0.01 mm of turned diameter and the second to within 0.001 mm (0.00004").
Headstock
All Petermann automatic lathes shared a common design of headstock assembly with a nitrided spindle running in either a pair of precision ball races or a parallel-bore bronze bush positioned behind the nose (with adjustment provided by being drawn into a tapered housing) with, at the other end, a pair of high-precision contact ball races capable of "micrometric" adjustment". Spindle end play was taken up by ring nut and, to reduce interference with the spindle, an additional bearing was used to take axial pressure and belt tension from the overhung (flat-belt) drive pulley. The collet was drawn into its taper by balanced, toggle arms fitted, on the larger models, with roller-equipped ends.
Cams and Camshaft
All-important, the cams that actuated the tool slides and accessories were turned by a single camshaft-like assembly mounted at the back of the bed and parallel to it - with the powered drive originating from worm-and-wheel gearing inside the cabinet that turned a train of compounded changewheels connected to a 4-step round-rope pulley. The drive then passed up the back of the machine to a similar pulley at the top connected to a second set of worm-and-wheel gears - with a hand drive provided by a capstan handle at the front. The camshaft was rigidly held in three bearing blocks, two of which were integral with the bed with the third easily removable to ease the chore of changing cams. At the headstock end of the camshaft two cams were responsible for opening and closing the spindle collet and, at the other, cams for the side-tools. On the end of the camshaft was a face-cam, the action of which caused the headstock (fastened to a hardened steel block on its underside) to be moved forwards and backwards through the action of an adjustable lever. Because the action of the various cams was interdependent, it was necessary that they be very accurately made and the sliding cam followers required sharp edges (roller tappets were only possible on the screw-head-slotting apparatus) The "sharp-edge" requirement was necessary because any radius on the follower would have been transmitted to the workpiece where, instead of a clean edge, a bevel would have been formed. As a result of this requirement - and to improve longevity - the cams and their followers were usually hardened. Whilst a selection of ready-made cams was available - and the factory would pre-make them for specific jobs - the best could be got from the machine only by the operator (or "setter") calculating and them making a particular form for each job. To assist in this matter Petermann offered a variety of cam-cutting machines to speed up an otherwise laborious process and the comprehensive operator's manuals all contained (often in dedicated supplements) detailed instructions for cam design and manufacture.

A number of Petermann P7 Automatics in a Swiss factory. The lathes on the right are all equipped with Robotbar automatic stock-loading units

Drive System
Older type of Swiss-Auto from all makers were driven by flat belts from overhead line shafting but, by the end of the 1920s, most makers of professional machine tools, including Petermann, were fitting self-contained drives with built-in motors and countershafts or speed-change gearboxes. However, even when provided with an integral drive unit, the complexity of the Swiss-Auto (especially in the confined area of the headstock) somewhat restrained the designers of the smaller models in their ambitions to provide a decent range of spindle speeds. In Petermann's case the problem was solved on the No. 0 by passing the drive through a simple gearbox fitted with "pick-off" wheels that the operator could change himself. Although the speed range was limited, because all work was small - and automatically completed - only a narrow range of higher revolutions was required (a maximum of 12,000 r.p.m was needed on some models with a range from 3000 to 8000 being common) and the system worked commendable well and with great reliability.
Working
Fitted with an automatic bar feed - Petermann's term for this was the
Robotbar - it was usual to run these lathes unattended for very long periods, the only requirement being to keep the bar-stock hopper topped up (as in the picture above).
Shown below is a now rare No. 0 set up for screwcutting and with a screw-head slotting attachment mounted (the slide-like assembly rising from in front of the headstock spindle). When turning steel on these lathes it was especially important that a continual flow of coolant (provided by a geared-driven pump) flooded over the tools: this cooled them (so limiting expansion and consequent changes in the turned dimensions), washed away swarf and extending tool life. Although not as essential when turning brass, it was common to keep the flow running to give the additional benefit of an improved surface finish..
Accessories and Attachments
One important advantage of the Swiss Auto was the ease with the machine could be adapted to mount ancillary equipment, typical and popular examples being single, double and triple-drilling units, thread-cutting attachment, drilling and thread-tapping accessories and a device to slot the heads of tiny screws. All these units were provided with a separate and comprehensive, well-illustrated instruction manual of the highest quality. As an example of what could be accomplished on the 5-tool model P-7, it was possible to manufacture a complex
regulator key of out of bar stock by fitting four turning tools, one parting-off tool, a vertical milling spindle in tool position 4, a stopping device on the headstock spindle to keep it stationary whilst milling, a wire camping device for holding the material during the return movement of the spindle with the collet opened--and a chip separating device. Thus set and fed with bar, the machine would turn out thousands of components without any intervention save to change tooling as it wore. The screw-head slotting device was similarly interesting and its method of operation typical of the complex manipulations necessary to accomplish this sort of work. After parting off, the partially-finished screw was supported in a tiny tube on the end of a swivelling arm; the arm brought the screw in front of a circular saw (driven from a belt at the rear of the machine) but with a little spring-loaded brass pressure sheet with a slot in its front (just wide enough to allow the saw blade through) imposed between saw and screw. The effect was to push the screw firmly onto its seat and allow the slot to be made. After this action, the arm moved backwards, a rod pushed the screw out of its holding tube and the finished part tumbled down a brass slide into a hopper. Two cams were used, one to move the arm forwards and backwards and the other (a face cam) to give a swivelling action - the end position of which was adjustable using stop-screws. As the operation was always identical, the cams were made as one unit and, being highly stressed and prone to wear by an especially long (swivelling) arm, the tappets (followers) were fitted with rollers..

The rare No. 0 Petermann Swiss-Auto. This lathe is fitted for screw-head slotting and screwcutting

In addition to the screw-head slotting attachment, screwcutting this Petermann also has a side-mounted cut-off tool slide

A view down onto the worm-and-wheel driven camshaft. This was held in three bearing blocks--two part of the bed with the third removable to ease cam changes. To the left of the bronze worm wheel can be seen the mechanism that opened and closed the spindle collets and, to its right, the cams for moving cutting tools and driving accessories.

A closer view of the collet opening and closing mechanism

The cam arrangement for the headstock spindle sliding movement. A peg, on the end of an arm, was made to run against the periphery of a disc formed with cut-outs in its face and mounted on the end of the camshaft. As the peg was caused to rise and fall by the uneven face of the disc, its movement was conveyed by the arm to a block, carried in an adjustable slot and from there to bear against the end face of the headstock. The headstock casting was fastened to a hardened block on its underside.

A view into the headstock showing the two small levers used to open and close a collet by pressing it onto its seat over an internal tube

Drive from an upper shaft passed through pick-off gears (top right) to a lower shaft fitted with worm-and-wheel gearing that, in turn, drove a set of changewheels connected to a pulley on the back of the stand used to drive the camshaft.

Drive to the camshaft originated from enclosed worm-and-wheel gearing inside the cabinet that turned a train of compounded changewheels connected to a 4-step round-rope pulley on the outside of the stand. The drive then passed up the back of the machine to a similar pulley at the top connected to a second set of worm-and-wheel gears.

Rear of the machine: drive to the camshaft was by 4-step pulley and round  belt. To the right can be seen the auxiliary drive up to a screwcutting attachment.

A fast-and-loose pulley arrangement (left) allowed the spindle to be stopped and started at will whilst allowing the motor to keep running. The large capstan wheel at the front was for hand operation of the camshaft