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A development of the Mk. 1 Model M, the 4" x 18" Mk. 2 Smart & Brown Model M was introduced during 1948 and improved even further on the original, beautifully-made pre-WW2 German Boley machine - of which full details can be found here.
Sold only on a cast-iron stand, the latter was a one-piece affair with an integral chip tray and the motor-countershaft unit held on a hinged plate beneath the headstock. Electrical equipment was built in - normally comprising a push-button, no-volt-release starter and a reversing switch - with the coolant tank and motor held in back. A narrow door at the front gave access to the over-centre belt-tension release lever - a screwed rod being provided for the final setting.
Running in adjustable, tapered bronze bearings (2" diameter by 2 13/16" long at the front and 1 9/16" x 2 7/32" at the rear), the hardened, nickel-steel spindle was bored through 63/64", fitted with a 1.75" x 8 t.p.i. nose and carried a 3-step flat-belt drive pulley. Fitting directly into the spindle were drawtube-retained collets of the 4A type with a maximum through bore of 3/4" (square 1/2" and hexagon 5/8") - though at extra cost the makers could also provide collets of the step and disc type together with their necessary opening and closing rings. Also available, as an option, was a kit (reference SB.19) to provide a lever-action closer for production work. Interestingly, the collets are almost identical to the Schaublin Type W25 - though the seat in the headstock spindle differed by a couple microns - probably a case of S & B putting the spindle bore "on size" - whereas Schaublin chose to put the collet "on size" and added 5 microns to the spindle bore.
Backgears, at a ratio of 5 : 1, were of the smooth-running helical type, all hardened and ground - the complete assembly giving, when fitted with a 3/4 h.p. 3-phase 960 r.p.m. motor, a range of six spindle speeds: 66, 108 and 183 r.p.m. in backgear and 480, 752 and 1300 r.p.m. in open drive. Equipped with the optional 1 h.p. 1440 r.p.m. motor speeds became 99, 159 and 275 r.p.m in backgear and 720, 1128 and 1950 r.p.m. in open drive.
Screwcutting and power feeds were provided by a set of 14 changewheels, neatly stored in a fitted wooden rack within the stand with room left for extra gears. Running down the centre line of the bed (where it was protected from swarf and dirt) the 1-inch diameter, 6 t.p.i. leadscrew was used only for screwcutting. A separate shaft drove the power sliding and surfacing feeds with a plunger lever, positioned just below the screwcutting chart, selecting between the two and provided with a middle, neutral position. Using just the standard changewheels, a range of English pitches could be generated from 4 to 60 t.p.i. with power sliding feeds ranging from a slow of 0.015" to a maximum of 0.0010" - and power cross feed set from 0.0075" to 0.0005", all rates being per single revolution of the spindle.
Massively constructed, the carriage was equipped with both front and rear aprons, these being joined across the bottom for extra rigidity with the coupling plate used to carry the leadscrew clasp nuts.
Equipped with a No. 2 Morse taper, the spindle in the set-over tailstock had a barrel 1.25" in diameter with a travel of 3.5".
Weighing approximately 0.4 tons, the Model M was priced, in the early 1950s, at a heady £565 : 19s : 0d and occupied a floor space of just under 60 inches long by 24 inches wide - with a height of approximately 48 inches..
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