A Carstens-Swisten Model D.G. with the Chase Screwcutting Attachment. Unlike more sophisticated systems the operator's handle (at the left-hand end of the bed) not only applied the cut but also simultaneously engaged the Master Thread on the end of the headstock spindle.

The "Carstens-Swisten" 5.125" centre height precision plain-turning bench lathe was of conventional design for its type and, apart from a taper screwcutting facility, enjoyed no significant features that could be described as novel. Its construction also followed well-established principles for its class and it was built from the "highest grade tested material, absolute interchangeability, guaranteed accuracy to limits by Professor Dr. Schlesinger for highest grade precision lathe."
The flat top, beveled-edged 29-inch long bed was, if not properly hardened, made in a chilled cast iron for which the makers claimed an unusual toughness; the ways were ground, as one would have expected in a machine of this quality, to "limit gauges" and the back of the bed was provided with a full-length T slot into which could be mounted a detachable screwcutting attachment of the classic and very accurate "chase" type.
The headstock spindle was of "finest steel", case hardened and ground (on the bearing surfaces only) and ran in large phosphor-bronze alloy bearings that were adjustable against a hardened steel thrust ring and locking collars; the whole assembly was designed to require the minimum of attention over many years of high-speed use; the maker also offered, at no additional cost, the option of taper roller bearings. The spindle could accept draw-in collets or, being threaded at the end, ordinary screw-on chucks and faceplates. Whilst many precision bench lathes had "reversed" headstock pulleys (with the smallest diameter against the all-important right-hand bearing so that more metal could surround it) on the Swisten the pulley was arranged in the ordinary way with the smallest diameter to the left.
The compound slide rest had a long-travel top slide that could be rotated through 45 degrees in either direction and both micrometer dials were of the zeroing kind and graduated in 1/1000" intervals. The feed screws were claimed to be "large" (but of unspecified diameter and pitch) and of what the maker called "trapexoidal" (sic) and probably Acme form. The screw and their nuts were (unlike those on many other precision lathes) completely covered against the effects of swarf and the inevitable grit from the grinding operations that lathes of this type - their owners determined to make the most of their expensive accuracy - were often called upon to perform. The rear of the cross slide was machined to accept a parting-off toolholder.
A bed-mounted hand rest was also provided and equipped with both long and short of T rests.
As part of the specification the makers also boasted of their "pressure-gun" lubrication points - where the injected oil would not only have been more likely to reach its intended destination but also to have forced out any foreign bodies trapped between the surfaces.
A chase-type screwcutting attachment, described and illustrated at the bottom of the page, was amongst the lathe's accessories - unfortunately the manufacturer's publicity department neglected to include a list of these in the machine's sales literature.
The lathe came complete with: a draw-in collet tube together with collet-mounted male and female headstock centres and a spindle-thread protection nut; a catchplate of the dangerous type where the drive-pin slot was open to the outside; a compound slide rest and a separate bed-mounted hand-rest with two lengths of T; a pressure oil gun, tool tray, test chart, male and female tailstock centres, the necessary spanners and a single-speed countershaft with ring-oiled bearings.
The tailstock was fitted with a No. 1 "short" Morse taper "through barrel" that was always, no matter how far extended in either direction, always fully supported within the casting; both an engraved barrel and a micrometer collar were fitted to indicate travel..

The Carstens-Swisten lathe, like many in its class, could be fitted with traditional "chase screwcutting" - in this case of a relatively simple construction - where a T slot, which ran down the back of the bed, held supports that carried a horizontal sliding shaft to which was attached, on the top of vertical arm, a screw-adjustable toolholder capable of mounting special single-point thread-chasing tools. Above the shaft at the headstock end of the lathe, and held between the arms of a clevis pin, was a "Follower" that engaged under spring pressure with a threaded steel hob (or "Master Thread") fitted over the end of the headstock spindle. The Swisten "Follower" was unusual in being a phosphor bronze "star" that carried 5 different pitches of thread, so reducing the number of followers needed and the frequency with which they had to be changed.
Besides being able to cut parallel threads the unit was also cleverly arranged so that short tapered threads could be generated. The mechanism for this appears to have been: the slotted arms of the clevis, the spring loading of the follower and the fitting of an adjustable two-part "guide plate" (to the left-hand end of the bed) against which a hardened screwed rod bore. With the spring pushing the follower against the spindle-mounted hob, lowering the engagement handle started the screwcutting process and the sliding shaft was driven along the bed; as it moved so the hardened pin was made to bear against the guide plate - though how the guide plate was set to the required angle is not clear - and the arm was moved backwards causing the cutting tool to move away from the workpiece. The angle of the taper was, of course, limited to the degree that the guide plate could be set over from parallel.
Whilst this system produced absolutely accurate threads, and was especially suited to delicate operations such as the thin-wall tubes used to construct such items as microscopes and telescopes, the length of thread that could be cut, and the number of threads per inch or mm that could be generated, depended upon the availability of an appropriate Master. Other disadvantages of the system as fitted to the Swisten were the lack of any changewheels to increase the number of threads that could be generated and the lack of a backgear for the essential slow-speed running required for screwcutting on a lathe of this type..
Similar chase-screwcutting arrangements can be seen on many of the pages devoted to the American makers Goodell-Pratt, Wade, Ames, Waltham, Pratt & Whitney, Potter, Rivett, Cataract, Elgin and Hardinge.

The Chase screwcutting attachment mounted on the back of the lathe bed. A flat spring steel blade was screwed to the back of the lever clamp to press the "Follower" (held in a sliding holder) against the "Master Thread".

Single-point thread chaser

"Belt-point" thread chaser

On the left the spindle-mounted steel hob - available in a variety of thread pitches. On the right the rotating bronze "Star Follower" with five different pitches in one compact unit.

Internal thread chaser

An indistinct logo from the bed foot of a Swisten lathe.