Of all the very many watchmakers lathes pulled from cupboards and hiding places in basements, one of the most common must be by the German maker Wolf Jahn, a manufacturer founded in 1887 and always associated with very high-quality engineering. Of all the better-known watchmaker's lathe the Wolf,Jahn is the hardest to find literature for - and almost impossible to date an individual machine - except very generally. Lathes were Catalogued by numbers and letters e.g. "A", "AA", "AAA", "B"", "C", "D", "E", "F", "FF", etc. with the types being further categorized by the particular type of headstock and compound slide rest fitted and the stand and drive system employed - of which there was wide choice. However, the system was not perfect and many of the smaller types - being built up from a choice of components, could not be given a specific model designation. Although the majority the Wolf Jahn watchmaker's lathes encountered by the writer have been of the conventional light 6 mm collet, 50 mm centre height "Geneva" pattern (with a bar-bed lathe) and the heavier WW types in 50 and 70 mm centres (Models "A" and "AA"), the firm also made a wide range of  precision bench lathes in both plain-turning (Models "C", "D", "DD") and screwcutting versions (Model "LL") together with a number of finely-made and interesting  milling machines. Like their German competitors G,Boley, Lorch and Leinen, they also produced numerous specialised watch and clock-making tools and equipment for factories turning out such goods.
A once well-known distributor of tools for watchmakers was Hirst Brothers & Co. Ltd. of Oldham, Manchester and Birmingham. In their earlier catalogues, lathes by Wolf Jahn were branded as "Roscoe" when of the lighter "Geneva" type and "Lancaster" when of the heavier American WW design. Unlike other companies, Hirst Bros. did not try to disguise these facts but stated them clearly in print.
If you have a Wolf Jahn machine tool, or can assist with copies of company sales or technical literature the writer would be pleased to hear from you..

Probably a Wolf Jahn Model LL, and typical of the very high quality toolmaker's lathes made during the years spanning the 19th and 20th centuries, this lathe of approximately 4" x 30" has all the features required of a decently-specified machine: detachable gap bed, backgear, screwcutting through a tumble-reverse mechanism, compound slide-rest and a decent-sized hole through the headstock spindle.
While this model used a conventional flat-topped bed with angled sides a similar backgeared and screwcutting model was offered with a bed that more closely resembled those used on traditional plain-turning precision lathes.
The lathe shown above would also have been available as a plain-turning bench model without the screwcutting and backgear - rather on the lines of the very similar and contemporary Lorch Schmidt model.

The crank-handle feed-screw levers are typical of the period, as is a lack of micrometer dials with users at the time becoming skilled at using inside and outside callipers of various kinds to transfer measurements from a steel ruler to the workpiece. Although the top-slide screw is left exposed on the left-hand side of the top slide, the lathe may well have been originally equipped with a sheet steel cover to protect the cross slide screw.

The headstock spindle was glass-hard and ran in hardened, ground and lapped steel bearings. Although some makers did fit very narrow, finely-made ribbed cast-iron backgear guards to their lathes those shown above may well have been added by a precious owner.

An extension to the back of the headstock-end bed leg provided a platform to accommodate a countershaft unit. At a time when most of these machines would have been driven from an already-installed overhead line-shaft system the idea of making provision for a self-contained drive was relatively new. Note, just visible below the chuck, the two screws that acted to locate the bed's detachable gap section

This Wolf Jahn lathe, like many in its class, has been fitted with traditional "chase screwcutting" where a sliding bar, supported in an extension to the rear of the headstock casting, carried a 5-start threaded follower that engaged with a "master thread" carried on the end of the headstock spindle.  At the other end of the bar was a toolholder carrying an appropriately-profiled tool that generated a copy of the master thread on the workpiece. On the Wolf Jahn an adjustable stop kept the bar level and also limited its travel.
While this system produced absolutely accurate threads, and was especially suited to delicate operations on thin-wall tubes used to construct such items as microscopes, the length of thread that could be cut, and the number of threads per inch or mm, depended upon the availability of the appropriate thread master.
A very simple form of this screwcutting mechanism can be seen on the Goodell-Pratt  whilst similar arrangements, differing only in the detail of their construction and versatility, can be seen on the pages devoted to the precision lathe American makers:  Pratt & Whitney,  Ames,  Potter, Waltham Machine Works and Wade.

Component parts of the Wolf Jahn chase-screwcutting attachment. Whilst some precision bench lathes could be adapted to this form of screwcutting without modification (e.g. by mounting the mechanism in a T slot that ran down the back of the bed) on some makes a different headstock and other components were required.