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      email: tony@lathes.co.uk
      Home   Machine Tool Archive   Machine-tools Sale & Wanted
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      OKUMA Type LS Precision Lathe
      - also built as the Dong Yang -

      Headstock   Carriage   Screwcutting Gearbox & Drive   Tailstock

      A Manual and Data Pack is available for the
      Okuma LS Lathe together with other Okuma literature

      Although the Okuma  company, based in the Okuma Machinery Works in Nagoya, Japan, has made a wide variety of products over the years - including automobiles, looms, spinning mules and even cigarette packaging equipment - it is better known for machine tools and today concentrates on a range of advanced CNC lathes and machining centres. One of its most popular and widely-sold conventional lathe of the 20th century was the "Type LS Productive", this model being  typical of the company's range of high-quality, precision lathes. It was available with swings of 450 and 540 mm (17.7 and 21.3 inches) and with between centres' capacities of 880, 1250 and 1500 mm (34.6, 49.2 and 59 inches). Notable for its very deep, rigid bed, clean lines and superb detailing, the LS also had a number pf thoughtful design features to aid the operator in the production of high-quality work. It is sometimes found with "Dong Yang" badges from a maker based in Seoul, Korea - though if the copy was officially sanctioned by Okuma is not known.
      Made from a high-tensile, close-grained semi-steel cast-iron, the bed carried inverted-V-ways that were high-frequency-induction hardened (and ground) and featured a very wide front way with a deep inside angle (as probably first used on the American Wade precision lathe) to both spread wear and aid the absorption of tool thrust. Although not quite meeting the rule-of-thumb that says that the bed of a toolroom lathe should be as wide as the centre height, at 390 mm it came very close. As the bed ways met the headstock the pair for the tailstock stopped short, forming a slight gap to slightly increase the maximum diameter capacity.
      Although a very substantial, one-piece cast-iron cabinet base was used, this had an inadequately-sized tool-storage compartment in the right-hand leg. While the coolant pump was accommodated neatly within the base of the machine, and drew its supply from a cast-in tank, the standard-fit chip tray had to be removed from the rear of the machine, thus limiting the number of places within a workshop where it could be positioned. The whole assembly was levelled by jacking screws housed in six of the stand's eight mounting pads.
      A particularly massive and rigid iron casting, the headstock was formed as a closed box with the minimum of flex-inducing openings in its sides and ends; it was fastened to the bed by a total of nine bolts, with two adjusting screws for alignment. It held spindles that were all of heat-treated, alloy-steel running on ball or roller bearings with the tooth flanks of the gears case hardened and ground; a proper lubrication system was fitted with a built-in oil pump to circulate filtered oil around both the headstock and screwcutting gearbox. To encourage regular maintenance, sight-glass oil-flow indicators were fitted (to let the operator know that the system was functioning correctly), and both the oil tank and filter were mounted under the left-hand transmission covers to allowed immediate and unobstructed access .
      Continued below:

      Continued:
      Dynamically-balanced, the 52 mm (2-inch) bore headstock spindle was made from a high-tensile, alloy-steel forging; it was hardened by a heat-treatment process (giving a reading of 65 to 80 shore along its length), ground finished (including the gear splines) and assembled in a dedicated-for-the-purpose, air-conditioned room. To protect against the ingress of dirt carried in by oil, its bearings were of the grease-sealed, attention-free type. Three bearing were used, all of the specially-selected, super-precision type with double-row cylindrical rollers at each end and a pair of angular-contact type as additional support in the middle. The spindle was bored for a No. 6 Morse taper centre, but normally carried a hardened bushing to reduce this to a No. 4 Morse for regular work; a special "centre push-out bar" was provided by which means the headstock centre, or adaptor sleeve, could be safely removed without recourse to hammering - and the consequential (potential) harm to the spindle's accuracy. The nose was of the Standard American A1-6" type that allowed chucks and faceplates to be bolted very accurately, hard up against the spindle end, as close as possible to the front bearing, and registered there by a short taper. If the time it took to unbolt a spindle fitting was a concern, then an ordinary D1-6" fitting, with its "quick-action" locking pins, was available at extra cost.
      A drip-proof 10 h.p.  (or optionally 7.5 h.p.) motor was housed in the base of the machine and drove via three V-belts (that passed around two jockey pulleys, one of which could be used to set the tension) to a constant-speed layshaft within the headstock. |Twelve speeds were provided, set so as to cover the majority of the jobs that the lathe might be called upon to perform; cleverly, instead of staying within the conventional geometrical progression, the highest and lowest speeds were each removed from the speed immediately next to them by a factor of approximately 2, this giving, in the standard configuration: 35, 63, 85, 120, 160, 210, 290, 390, 525, 730, 970 and 1800 r.p.m. Three other ranges were optional, one slower and two slightly faster; the slowest range was: 23, 42, 55, 78, 105, 140, 200, 260, 350, 485, 650 and 1200 r.p.m. and the two faster: 38, 70, 95, 130, 180, 240, 330, 440, 600, 810, 1100 and 2000 r.p.m. And: 42, 80, 105, 145, 200, 260, 350, 480, 650, 900, 1200 and 2200 r.p.m.
      Spindle speeds were changed by a three-position lever on top of the headstock - this providing High, Low and Neutral positions - together with a simple rotary control on the face of the headstock. The stopping and stating of the spindle was controlled by a third shaft, parallel with the leadscrew and powershaft, and fitted with a lever at the headstock end of the bed and another on the right-hand wall of the apron - a useful safety feature, especially on the long-bed model when the headstock control might have been out of reach.
      Screwcutting and power feeds were arranged from a dual metric-English gearbox, pump-lubricated with a filtered oil supply shared with the headstock; the unit was completely enclosed and contained hardened and ground shafts and gears running on anti-friction bearings. Threads and feeds were driven separately, from a leadscrew and power-shaft respectively, and selected by neat, rotary-movement levers, there being no pull-and-slide controls to wrestle with. Sliding-feed rates varied from 0.05 mm (0.002") to 0.7 mm (0.028" ) which was exactly 1/10 of the threading feed rate produced by same position of the selector positions; the power-cross feed rate was arranged to be exactly half sliding rate. Feed direction was selected by a simple push/pull button on the apron and engaged by a lever operating a quick-action, drop-out worm that gave a disengagement action that was light yet positive, no matter how heavy the cutting load at the point of release. The drop-worm and feed clutch were part of a spring-loaded safety-overload mechanism that could be adjusted (by special spanners included in the tool kit) to set the point at which the feeds tripped out before the drive system was damaged. As a safety feature the push/pull feeds' selector was arranged so that, at the end of a longitudinal feed towards the headstock, pulling the button out to engage power cross feed caused the tool to withdraw outwards towards the operator. A very useful fitting (designed to assist with critical finishing operations, changing from roughing to finishing cuts or on multiple-diameter copy work) was a mechanism to halve the feed rates by operating a control lever on the top of the carriage. The direction of the feeds and threads could be reversed through a tumble-reverse-like mechanism controlled by a single lever, situated under the spindle-speed chart on the face of the headstock. Also fitted as standard to the LS, was an automatic knock-off on the carriage longitudinal feed; this system took advantage of the cast-iron stand where a steel rail, let into the front edge of the chip tray, carried a pair of micrometer-adjustable stops that could be quickly slide into any position desired. The stops not only made for accurate and repeatable boring and turning operations but also as a useful safety device with the operator able to leave a long turning job knowing that, when complete (whether moving towards either the headstock, or tailstock), the cut would finish automatically.
      32 English threads from 4 to 56 per inch, and metric pitches from 0.5 to 7 mm were available with the change from one to the other by a single lever - whilst the changing of a single 72t gear on the changewheel drive allowed Module and DP pitches to be generated. The 32 mm diameter, 30 degree Acme-threaded leadscrew was manufactured from a heat-treated alloy steel and finished to an accuracy of 0.03 mm per 300 mm (pitch error); it was held in super-precision ball bearings in the tailstock-end bracket and incorporated an end-play adjustment.
      Continued below:

      The high-tensile, close-grained semi-steel cast-iron bed carried inverted-V ways, high-frequency-induction hardened (and ground) and featuring a very wide front way with a deep inside angle (as probably first used on the American Wade precision lathe) to both spread wear and aid the absorption of tool thrust; although not quite meeting the rule-of-thumb which says that the bed of a toolroom lathe should be as wide as the centre height, at 390 mm it came very close.

      Continued:
      In line with the rest of the machine, the carriage assembly also reflected careful thought in its design and construction. Heavily-constructed, the one-piece, double-wall apron held two pumps that drew oil from a sump in the base and distributed it to both the apron mechanism - in which all gears, except the alloy-bronze worm wheel were in high-tensile steel - and the bed and cross-slide ways; one pump one worked automatically whenever the carriage was moved by hand, or under power, while the other, with a plunger action and positioned at the upper right-hand front of the apron, was used to supplement the supply whenever the carriage was stationary on the bed, or prior to starting the machine. A knurled knob was provided to control the volume of oil reaching the slides and a sight class, in the wall of the apron, showed the amount of lubricant left in the reservoir. Because the (very large) carriage hand-traverse wheel was fitted to the left-hand side of the apron, a curved metal guard was fitted to protect the operator's hand from hot turnings; the wheel was fitted with a large, zeroing micrometer dial with which carriage travel could be measured down to 0.001 inches.
      Superbly made and finished, the compound slide assembly had hand-scraped slides and was fitted as standard with a properly constructed, indexing 4-way toolpost machined from an alloy steel forging and turning on a ball-bearing mounted, hardened and ground shaft. Designed to accept 19 mm (0.75") tooling as standard, the unit was capable of accepting cutters up to 25 mm (1") square. The 140 mm (5.5") travel top slide could be rotated 90-degrees in each direction from zero and was locked down by two T-headed socket screws turning in a circular T-slot. Although the flush-mounted socket screws contributed to the neat appearance of the slide, to the annoyance of the operator, before they could be released to swivel the slide, they had to be cleared of swarf (though it would not have been hard to turn up a couple of easily removed blanking plugs). With 270 mm (10.625") of travel the cross-slide was of the full-length type, so spreading wear across the whole length of its ways and making backlash adjustment an easy affair. Both slides used tapered adjustment gibs, with abutment screws at both ends, and each was fitted with a handy locking lever. Both micrometer dials were of a decent size, finely engraved, fitted with a vernier scale that allowed settings down to as little as 0.01 mm (0.0005") on diameter and with that on the cross slide locked by a screw through its end face - so preventinh a change of reading as the assembly was nipped up. Although the cross-feed dial was normally supplied showing the amount taken off the radius of a workpiece, the makers offered, to special order, one where the graduations indicated the reduction in diameter. Both Acme-form cross and top-slide feed-screws were supported at each end in ball bearings and their nuts were adjustable to eliminate backlash. Although the writer is unable to confirm the fact, it seems that machines supplied for the UK market were fitted as standard with what was normally listed as a desirable extra - a hardened cross-feed screw running in an oil bath.

      As the bed ways met the headstock the pair for the tailstock stopped short, forming a slight gap to slightly increase capacity.

      Continued:
      With its Kerry-like angled drive to the barrel, the distinctive tailstock was of box-construction and ran on its own pair of V and flat ways; two clamps were fitted to lock it to the bed - one an ordinary lever-operated, over-centre typee for normal work and the other, for heavy-duty turning, activated by a nut beneath the handwheel. Two rather ingenious features were fitted to the tailstock: the first allowed one-handed repositioning, the second could quickly advance the barrel: the "one-handed" assistance consisted of spring-loaded bakelite rollers mounted within the base; when the bed clamp, or clamps, were released the tailstock rose up slightly on the rollers and could be pushed about by hand with relative ease. The "barrel quick-advance" was operated by a rear-mounted lever that gave a travel about 30 mm (2.2 inches) with a single stroke. The barrel, fitted with a No. 4 Morse taper and a slot to knock out drill tangs, was hardened and ground for its entire length, graduated from 0 to 150 mm at 5 mm intervals (each division representing one turn of the hand wheel) while a micrometer dial on the handwheel read in 0.1 mm (0.05 inches) intervals. The end of the barrel was surrounded by a wiper, clamped within a case and scribed from the edge of the case, to the outside of the barrel casting, was a centre-height line to assist with the setting of cutting tools.
      Although both  different single and multi-colour finishes were also available to special order (though seemingly rarely specified) the lathe was finished as standard in machine-tool grey. Supplied with each lathe were: three V-belts; a set of changewheels for DP and module threading; one  200 mm diameter faceplate, one No. 4 Morse-taper centre; one No. 4 Morse-taper cemented carbide-tipped centre; one No. 6 Morse-taper centre sleeve; one centre push-out bar; one set of levelling washers; one set of electrical spare parts; one set of operating tools in a metal box; a lubricant compound ("metalube") a tin of touch-up paint and a brush; an instruction book and a copy of the final assembly test. The usual extras were offered: coolant equipment with a 0.125 kW pump, hydraulic copying, taper turning, 3 and 4-jaw chucks, 400 mm faceplate, fixed and travelling steadies, chuck guard, quick-change toolpost, extra changewheels for cutting coarse and 11.5 and 27 t.p.i. threads, a hardened, oil-bath lubricated cross-feed screw and a direct-reading (off diameter) cross-feed micrometer dial.
      Approximately 2.355m long in short-bed form and 2.805m as a long bed, weights varied from 2000 kg (4400 lbs) for a short-bed 450 mm swing example to 2300 kg (5060 lbs) for a long bed 500 mm model. The smallest LS (450 mm centre height by 800 mm between-centres) weighed 2150 Kg (4,740 lbs) whilst the largest (540 mm centre height by 1500 mm between centres) turned the scales at 3250 Kg (7,165 lbs)..

      Headstock   Carriage   Screwcutting Gearbox & Drive   Tailstock

      A Manual and Data Pack is available for the Okuma LS Lathe
      together with other Okuma literature


      OKUMA Type LS Precision Lathe
      - also built as the Dong Yang -
      email: tony@lathes.co.uk
      Home   Machine Tool Archive   Machine-tools Sale & Wanted
      Machine Tool Manuals   Catalogues   Belts   Books   Accessories



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