di Marcantonio Varinelli
Milano - via Mont Video 21"
- this high-class, precision plain-turning lathe is the only known example of its genre manufactured in Italy. Looking remarkably like a German Karger (even the neat countershaft with its single central bearing and pulleys overhung at each side is of the Karger type), nothing is known of the claimed maker, OMPP - the writer never having encountered a machine by them before. Allowing for the Italian reputation for innovate engineering, one can be sure that they would have made other types as well so the possibility is that other way well be discovered.
Although this type of "bench precision lathe" was first made in 1862 by the American Stark Company, the design (in this particularly elegant, vintage form)), persisted into the 1940s with the example shown below - if the suspiciously-large feed-screw micrometer dials are original - most likely to have been manufactured between 1930 and 1945. Of around 100 mm centre height and accepting perhaps 500 mm between centres, the OMMP was absolutely typical of its type, with a very deep, heavy and rigid bed that carried a plain bearing headstock with flat inside and outside faces. The compound slide rest had the usually very long-travel top slide - the only way of obtaining a long cut on a lathe without a means of traversing the whole carriage - and a tailstock with the casting cut away in the centre to reveal ruler-engraved lines on the long-travel spindle.
Probably available as an option, the lathe was fitted with chase screwcutting of the "sliding-spindle type", this using a rotating multi-threaded "star" master thread - each with six different pitches machined into their periphery - carried on a plate that could be elevated by a lever to engage with a matching thread on the end of the headstock spindle.
Instead of the threading tool being made to move along the job as with an ordinary chase-type screwcutting arrangement, the headstock spindle was arranged to slide forwards and backwards in its bearings, the cutting tool remained stationary. Widely used on ornamental turning lathes in the 1800s, in more recent times the system was adopted by such German firms as Lorch ,Wolf Jahn and Auerbach and the Schaublin from Switzerland; the smallest model known to have incorporate it being the 50 mm centre height Wolf Jahn Model AA. The arrangement was also a feature of most "Swiss-Auto" mass-production lathes, often used for the manufacture of tiny parts - and is still in widespread use today on such machines, though these are now (of course) fitted with CNC controls. The last conventional plain lathe on which it appears to have been available was a version of the Schaublin 102, this being available into 21st century.
Designed originally for use by optical instrument makers, who needed a short but very accurate thread, a disadvantage of the "chase" system was the need to keep in stock a range of master threads and their matching, spindle-mounted followers. However, with the limited range of thread pitches required this was not unduly expensive and usually included in the set (to allow the manufacture chuck backplates and other work-holding units) would have been one coarse-pitch pair with the same thread used on the lathe's headstock spindle nose.
If you have a OMMP lathe, the writer would be delighted to hear from you.
Se hai un tornio OMMP o qualsiasi altra documentazione su di esso, lo scrittore sarÓ lieto di avere tue notizie