Holbrook Model B No. 8 Toolroom Lathe 4" centre height and 20" between centres.
Shown fitted to the optional polished-oak cabinet stand, itself mounted on a cast-iron base, this beautifully made Holbrook lathe had detail touches that bore a passing resemblance to certain features of the superb American Rivett 608 precision toolroom lathe.
The stand, besides mounting a push-button starter and a lever switch for the two-speed electric motor, was able to incorporate an optional, self-contained, ball-bearing overhead drive to power grinding and milling spindles held in the toolpost - the lathe is shown with a grinding head so mounted.
The substantial bed of the No. 8 Toolroom lathe (it was considerably deeper than the lathe's centre height) was machined from an aged casting and the whole of the outer surfaces, in the manner of Rivett lathes, was milled and then ground to provide a superb finish. A single rear V way located the headstock and another, at the front of the bed, the carriage.
The two-speed motor and clutch drive, together with the 6.8 to 1 ratio backgear provided a range of 12 speeds spanning 43 to 1340 rpm. The hardened and ground spindle was bored 7/8" but both it, and the tailstock barrel, carried inadequate No. 1 Morse tapers. A set of draw-in collets, with a maximum capacity of 5/8", was provided with the lathe - as was a hand-operated, headstock-mounted brake to slow the spindle from high speeds.
The spindle, with a 1.75" BSF thread (British Standard Fine) was lapped to its tool-steel cone bearings that had both internal and external tapers - and included a simple method of adjustment for wear. The front bearing had a double-step taper with one part, set at 45 degrees, designed to take spindle end thrust in in one direction - whist the back of the bearing took the thrust in the opposite direction. By using this method of construction the makers claimed to limit the effects that temperature changes, caused by heavy-duty turning, had on the spindle's length. A conventional, rear-mounted backgear was fitted and the spindle bull-wheel ringed with 60 indexing holes.
The quick-change screwcutting gearbox, with nickel-chrome gears, provided 27 different threads and feeds - its drive from the headstock passing first through an oil-immersed gearbox that could engage or disengage the feed. Beneath the gearbox was a lever to operate the reverse for feeds and screwcutting; the large spur-type reversing gears were built into the bottom of the gearbox, ran in an oil bath and could be operated whilst the lathe was running at spindle speeds of up to 125 rpm.
Translation gears were provided to cut metric and BA threads and the leadscrew, which could be engaged and disengaged by a sliding gear where it passed into the gearbox, was used only for generating threads, a separate shaft, carrying automatic knock-off stops, being used to transmit power to the doubled-walled apron. The leadscrews were corrected against a master thread, that itself had been certified by the National Physical Laboratory as accurate to within plus or minus 0.0001 over any one foot length, at 68 F.
The heavily constructed apron was doubled walled with all its shafts fully supported on double bushes. The phosphor-bronze split clasp nut for screwcutting was also closely supported between the walls, instead of being overhung from the inner wall as was (as still is) common practice. The power sliding and surfacing feeds were engaged by friction cones, each with its own control and the threads and feeds selector was also apron mounted. The trip for the automatic apron-feed stops was provided with a micrometer adjustment marked in one-thousandths of an inch; rotating the dial gave an axial movement to a long sleeve that covered the stop rod and projected from each side of the apron; sliding clamps on the stop rod allowed a coarse setting of the disengage point to be made first. A dial thread indicator was neatly built into the apron and protruded through its front face.
The compound slide rest was fitted with rather small zeroing micrometer dials whilst the top slide, which could be swivelled through 360 degrees, reflected precision plain-turning practice by having an unusually long travel; T slots were formed in each of the apron wings.
Supplied with the lathe was a fast and loose, two-speed, , ball-bearing, wall-mount countershaft unit with foot-operated belt shifter, an 8" diameter T-slotted faceplate, fixed and travelling steadies and a hand Tee rest. Although no chucks were supplied, 9 collets from 1/8" to 5/8", mounted on a neat circular oak stand, were - together with a collet draw bar and a headstock spindle adapter sleeve.
The lathe was 4 feet 6 inches long, 1 foot 5 inches wide and weighed 440 lbs.
The lathe was later fitted with a geared headstock and variable-speed drive - with a rev counter mounted on a post fastened to the back of the stand. Details of this rare machine unknown and if you have one the writer would be pleased to hear about it.