Introduced during 1941, the SV-120 was produced as both the plain-turning but backgeared Model 120-TO - and the very much more complex backgeared, screwcutting and infinitely variable-speed Type 120-VM. This was the fourth screwcutting lathe to be offered by Schaublin and followed the pre-WW2 102 mm centre height Model 102-VM and Models 130-VM and 150-VM. Production ran until at least 1966 with the numbers built thought to be less than two thousand - not unsurprising considering the very high price..
With a centre height of 120 mm (4.7 inches) and a between-centres capacity of at first 500 mm (20 inches) but later 600 mm, the SV-120 was intended for toolroom use and had a bed arranged in a manner similar to that employed on the 102-VM - the front wall being extended to carry a V-way and at the back a rectangular way on which the carriage ran - but (unlike the 102-VM) with the bevelled-sided top altered so that the tailstock ran on its own flat and V way. In a similar fashion there was a rear "saddle" joined to that at the front by a section beneath the bed (that carried the leadscrew clasp nuts) so forming a rigid cage around the bed.
Fitted with a 1 : 5.3 ratio (oil-bath) backgear, the plain-turning models had a 2-speed motor that drove the spindle directly using a 3-step flat-belt cone pulley; sixteen speeds were provided with 75, 120, 150, 185, 240, 360, 750 and 1500 r.p.m. available in backgear and 380, 600, 750, 760, 920, 1200, 1500 and 1850 r.p.m. in direct drive. However, these speeds appear to have varied a little over the years (and would have changed in any case with 50 Hz and 50 Hz motors) with some examples being marked with 80 r.p.m. as the bottom speed and 2000 r.p.m. on top; however, owners report that the real bottom speed was closer to 60 and the highest just over 2000.To change the belt-driven speeds a typical Schaublin belt shifter mechanism was employed: a foot pedal lifting the motor and the combination of a knee-operated push rod (set between the stand plinths) and a 3-position hand lever (protruding from the front face of the stand) being used to flick the belt across to the next higher or lower speed.
One unusual feature of the SV-120-VM was a continuously-variable speed drive system working through the same headstock hearing as the plain model and available with either three or one-phase 2-speed 1.5/2.7 h.p. motors running at 715/1410 r.p.m. on late models and 750/1500 r.p.m. on earlier. The variable-speed unit was interesting (and resembled that used on some early primitive "cyclecars") where a friction disc was made to rub against a conical face with the ratio being changed by altering the radial position of the contact point. Needless to say, the Schaublin unit was beautifully constructed , worked smoothly and with the face friction material lasting several years before replacement was required. Drive to the headstock spindle was by a very wide, flat belt that ran over a single pulley supported at each side in its own ball races; with the drive transmitted from pulley to spindle through a peg all effects of belt pull were thus removed and the spindle had to take only those loads imposed by the cutting process. Spindle speeds spanned approximately 50 to 1750 r.p.m. and were altered by a large handwheel on the front of the stand in combination with a backgear lever on the headstock with another - connected to a control rod - on the apron. To select the required speed the large wheel was turned until the desired reading appeared on a dial immediately above it; at the side of the dial a conversion chart indicated the correct setting for the two levers.
Power sliding and surfacing feeds were separate from the screwcutting mechanism and driven by V-belt to a power-shaft set along the front of the bed - the pulleys being contained within a housing, covered by a hinge-open cover on the front face of the headstock. Feed rates were selected, on early machines, by a headstock mounted lever - later changed for a dial that carried red and green segments indicating the rates together with a central push-pull button that gave neutral when set centrally, a fast range when pushed in: 0.13, 0.20, 0.32 and 0.5 mm/min and slow when pulled out: 0.025, 0.040, 0.060 and 0.095 mm/min. Power cross-feed rates were set at half those of the sliding: 0.012, 0.02, 0.03, 0.05, 0.06, 0.10, 0.16 and 0.25 mm/min. However, on early examples of the lathe the range of feeds was much more limited: 0.025 to 0.172 mm/min longitudinally and 0.010 to 0.068 mm/min across. On all versions a lever on top of the feeds' box was used to reverse the drive - it could be moved safely at any speed with its middle position acting as a neutral and, by swapping over the drive and driven pulleys in the box beneath it, the rate of feed halved.
Taking W25 collets, the 25 mm bore headstock spindle has been found with a straight-through bore machined to fit W25 collets and without a Morse tapered section - though this was lsietd in some catalogue specifications. A quick-action, lever-operated collet closer was available and the spindle nose came with a flared, screw-on shield that kept swarf out when using collets.
Spindle bearings were of the highest quality, with that at the front being a double-row, cylindrical roller type (usually an SKF NN 3011-K-SP) and at the rear two ball bearings of the "magneto type" (SKF 7208-C15).
Screwcutting was by a set of 24 changewheels through a tumble-reverse mechanism (with, unusually, two separate arms to carry the gear) and a massive leadscrew set down the centre line of the bed that was grasped not by conventional double clasp nuts but a single half-nut that covered a sector of about 120 degrees. Leadscrew end thrust was taken at the tailstock end by apposing adjustable taper bearings and a bronze half-bushing beneath the spindle nose. The clasp nut arm pivoted at the back side of the carriage on a big wrist pin, but at the apron it simply sat on an eccentric and slid between guides. A separate oiling system was provided for the leadscrew, this being by a spring-loaded plunger with a rubber roller on its upper end riding in an oil bath in the clasp nut arm. So long as the oil level was kept topped up, this roller turned in the oil bath and "wiped" the leadscrew with lubricant - the system being reported by owners to work perfectly well.  Metric pitches available varied from 0.25 to 7 mm and English from 60 down to 4 t.p.i. Module pitches from 0.25 to 4 could also be generated.
Using a typically Schaublin arrangement, the compound slide rest featured a full-length cross slide - with two rear-mounted plain rectangular slots with threaded holes in the bottom for attaching accessories - and a long-travel, 2-T-slot top slide that, because it had plenty of clearance, was able to be fitted with an unusually large micrometer dial.
Although of limited capacity, the 120-VM was very heavily built - it weighed in excess of 850 kg - and was mounted (like the plain model) on a massively-built, rectangular-form, cast-iron cabinet with integral chip tray, the complete transmission assembly and neat, built-in electrical equipment..