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Liebert & Gürtler DLZ-300 Lathe

Manufactured from the late 1950s onwards in what used to be communist-controlled East Germany, the DLZ-300 came from a maker of specialist lathes, Liebert & Gürtler, a company  established in 1919 and still trading today Rasoma. The firm's range of lathes was huge, and included some spectacularly large examples; however, the type shown here (developed from a previous Model the FD-150) was of more modest proportions, weighing 1260 kg and with a centre height of 150 mm and taking just 600 mm between it's No, 5 Morse headstock centre and No. 3 Morse tailstock. Of pleasing proportions and built to DIN 8605, a specification for toolroom machines( werkzeugmachergenauigkeit), the lathe had a V and flat-way bed some 242 mm wide - this falling just short of that needed for the common classification of a true toolroom lathe where the bed width should be at least equal to the swing. However, this was still a very robust structure with walls of a considerable depth braced by diagonal ribbing and further strengthened by being bolted to a massive cast-iron stand.
Bored through 30 mm clear, the spindle ran in a large, adjustable bronze bearing at the front and a precision roller bearing at the rear - end thrust being taken by precision ball races mounted at each side of the front bearing. Fitted with a 68 x 6 mm pitch threaded nose (to DIN 800 specification), the spindle was driven by 4 V-belts from a 3.5 kW squirrel cage motor flange mounted to a splash-lubricated gearbox suspended on threaded rods and held within the left-hand end of the base. As with other lathes using this arrangement, the aim was to limit the effects of gear thrash on the surface finish of turned work. In order to relieve the spindle of the effects of belt pull, the V-pulley ran in its own bearings and, to help the maintenance department, the belts could be changed without having to dismantle the headstock, in the words of the maker: "
innerhalb von wenigen Minuten" (within a few minutes). In addition to the remote speed-change gearbox, the lathe was fitted with a low-speed "backgear" assembly inside the headstock - the design enabling the 6 highest speeds to be transmitted directly to the spindle and the 6 lower though torque amplifying gearing. It is believed that the makers offered three speed ranges, although only two were listed in the official specification; the first was described as "standard" with direct drive by belt giving 265, 375, 530, 750 1050 and 1500 r.p.m. and through backgear of 33, 47, 67, 95, 132 and 190 r.p.m. the second employed faster speeds with a high-range of 365, 530, 750, 1050, 1500 and 2100 r.p.m. and a low of 47, 67, 95, 132, 190 and 265 r.p.m. All gears in the drive system were made from a suitable grade of alloy steel with case-hardened and ground flanks. Lubrication was automatic, using a geared pump mounted on the speed-change gearbox and drawing oil from a remote tank; from there it was directed through pipework equipped with labyrinth and magnetic filters to the headstock, screwcutting and feeds gearbox and changewheel housing.
Control of the spindle was by a third-rod system, with the control handle pivoting from the right-hand face of the apron and so moving with it. Lifting and lowering the lever activated a 24-volt D.C. electromagnetic double-disc clutch-cum-brake unit fitted to the headstock input shaft; the  braking effect was activated by selecting reverse when running forwards, the acceleration in this direction being arranged at 1 : 2 and so able to being even heavy workpieces to a swift halt.
Carriage feeds could be by either a simplified feeds gearbox (listed as the Model V) or, as more commonly found on this lathe, a full screwcutting and feeds gearbox (the Model G). The full gearbox provided, via a  6 mm pitch leadscrew and without the need to change or dismount any changewheels, metric threads from 0.5 to 7 mm, Whitworth from 28 to 4 t.p.i. and diametral from 28 to 4 t.p.i. If module pitches were required these could be obtained by the substitution of two changewheels when the range generated ran from 0.5 to 7.  On both models an extra-fine feed attachment could be fitted, this consisting of a detachable V-belt drive from the headstock down to the screwcutting and feeds gearbox, with the normal gear drive able to be disengaged. Amongst the various options offered was a changewheel marked to assist with the generation of multi-start threads. Instead of the traditional Norton-type sliding-selector-with-plunger-engagement of feeds and pitches, the DKZ used a combination of a dial and rotary lever - the former having three windows, one each for threads and longitudinal and traverse feeds. Turning the dial to the required pitch gave a letter reading (A, B, C, D, E and F) that allowed a ball-type control lever to be set in the correct position. In addition, a mechanism was incorporated in the drive, selected by a single lever, to give pitches up to 8 times coarser or 5 times finer than standard (the readings on the selector dial then having to be either multiplied by 8 or divided by 5). Power sliding and surfacing feed rates were arranged in what the makers described as "Normal" and "Fine" ranges, the longitudinal in the former being from 0.07 to 1.1 mm/rev and from 0.008 to 0.12 mm/rev in the latter. As expected, the cross feed was arranged with a much slower set of rates: from 0.016 to 0.22 mm/rev in "Normal" and from 0.002 to 0.024 mm/rev in "Fine". Provided with each lathe as part of the standard equipment was a set of changewheels (36, 45, 87 and 90t) to extend the threading and feed ranges.
With all its shafts supported at both ends, the apron was of the enclosed box type with an oil bath in its base. Selection of sliding and surfacing feeds was by a single lever with engagement - in both directions - by a second lever that controlled a built-in spur-gear mechanism. To enable turning up to a shoulder, or against a bed stop, an overload clutch was fitted with its release load adjustable from the outside.
Of convention arrangement with decently wide V-edged slideways, the compound slide assembly was equipped with tapered grip strips.
Able to be set over for the turning of slight tapers the front of the tailstock was canted forwards sufficient to allow the barrel to reach over the cross slide and so permit the turning of very short pieces between centres.
If any reader has a Liebert and Gürtler machine tool the writer would be interested to hear from you.

Liebert & Gürtler DLZ-300 - developed from the earlier FD 150

Liebert & Gürtler DLZ-300 shown with the standard clamp toolpost but equipped with the optional rear toolpost and taper-turning attachment

Threading and power sliding and surfacing controls of the Model G with a full screwcutting and feeds gearbox

Power-feed controls on the Model V

The changewheel drive could incorporate, at extra cost, a gear marked to assist with the generation of multi-start threads

Drive came from a 3.5 kW motor flange mounted to a splash-lubricated gearbox held within the cabinet base suspended on threaded rods

View of the headstock with its top cover removed

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Liebert & Gürtler DLZ-300 Lathe