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【十一】
GA Lathe Model 212
Beautifully made, the little George Adams 21/2" centre height precision lathe has been a machine sought after by generations of amateur machinists - especially clockmakers - keen to get their hands on a genuinely high-quality product (though it must be said that the design quirks, present on nearly all George Adams's products, were present on this version too). Also found badged as the R.Kelly of Manchester & Liverpool, the lathe was almost certainly inspired by German Wolf Jahn practice with very small marks - usually saying just "Germany" in tiny letters - sometimes being found stamped on various parts using that company's recognisable style. In addition the accessories also confirm such a connection, being constructed in an identical way and directly interchangeable with the Wolf Jahn originals. Normally sold in plain-turning form, the 21/2" could also be fitted with two types of screwcutting arrangement: the first, using a straight shaft direct from changewheels to the top slide was at odds with the normal practice of using a keyed and universally jointed shaft; the second consisted of a proper bed-mounted leadscrew - in which latter form it is particularly rare. Made for several decades, from approximately 1900 until the mid 1930s, it had a bed of typically English/German pattern, being flat on top with the location for headstock, carriage and tailstock formed by vertical flat shears between the two ways. An unusual feature was the mounting of the bed feet - they were simply bolted to rather ugly-looking lugs formed at each end of the casting. However, being finely machines on both top and bottom surfaces - and located on the machined underside of the bed - the feet did add slightly to the bed's stiffness.
Like all "Precision" George Adams lathes, the headstock of the 21/2" followed the well-established pattern for a high-quality "Bench Lathe*" of having bearings made from opposed , hardened steel cones that closed down on similar hard cones fastened to or formed as part of the spindle. Provided a supply of clean oil was maintained, this type of bearing proved capable of almost infinite life - some American lathes (by Stark and Wade) having successfully absorbed over fifty years of commercial use without failure. The headstock spindle (or mandrel as it was then called) accepted a hardened, tapered insert that took standard 8 mm collets. This insert can, incidentally, be hard to see, being a very close fit within the 7/8" diameter, 20 t.p.i nose, and must be removed if use of the full spindle bore is required.
Designed to be driven by a round leather rope - or "gut" in popular contemporary parlance - the 3-step cast-iron pulley was locked to the spindle was a somewhat over-engineered (though delightful) collet-like method where the smaller end of the pulley was turned parallel for a short distance and slotted with four equally-spaced slits; a large clamping ring was slipped over the slotted section and tightened by four screws until it closed down onto the spindle - the arrangement can clearly be seen in the pictures below.
Equally neat, though not unique - it also being employed by Rivett - was the method of securing the "balanced" ball-ended handles on the very long-travel compound slide rest; a long screw, with its slotted head moulded so as to blend in with the end of the ball, passed right down the stem of the cross piece to engage with the end of the feed screw. The design of the compound slide assembly was unusual, and incorporated some weaknesses; the feed screws were 25 t.p.i. with brass micrometer dials, finished, on early examples, with a double rim and traditional "rope" knurls, engraved with divisions of 0.002". The slide rest changed over the years with some being in proportion to the rest of the machine (with the expected lengths of travel) while other were noticeably different with considerably longer cross slides and more modern-looking micrometer dials. Unfortunately the top slide - which on all models had at least a useful 3 inches of movement - had no degree marking for its swivel settings; and, equally disappointing for a quality lathe (though in line with later Schaublin practice), was the use of a long horizontal slot in the tailstock casting to act as a clamp for locking the (short) No. 1 Morse-taper barrel. The danger of the casting being over tightened, and broken off, was mitigated against (to some extent), by the provision of two adjustable stop screws that passed through the slot - one at each side of the clamping screw; the general arrangement of the tailstock slit can be seen in the third picture below.
An unusually wide variety of accessories was available for the lathe enabling it to be used for grinding, screwcutting, precision sawing, milling and light production work.
Original colours used on George Adams lathes included plum red and emerald green.
*Including: American Watch Tool Company, Arrow, B.C.Ames, Bausch & Lomb, Benson, Boley, Bottum, Boxford, B.W.C., Carstens, Cataract, Cromwell, Crystal Lakes, CVA, Derbyshire, Elgin, Hardinge, Hjorth, Juvenia, Karger, Leinen, Levin, Lorch, Mikron, W.H.Nichols, Potter, Pratt & Whitney, Rambold, Rebmann, Remington, Rivett, Saupe, Schaublin, See (FSB), Sloan & Chace, Smart & Brown, T & L.M., U.N.D., Van Norman, Wade, Waltham Machine Works, Weisser, Wolf Jahn and (though now very rare), Frederick Pearce, Ballou & Whitcombe, Sawyer Watch Tool Co., Engineering Appliances, Fenn-Sadler and the "Cosa Corporation of New York.."
The standard GA 21/2 plain-turning lathe.
Screwcutting attachment driving through a straight shaft to the top slide - an arrangement at odds with the normal practice of using a keyed and universally jointed shaft
The maker's lever-action toolpost grinding attachment fitted neatly into the cross-slide T slot. The unit was very well built and incorporated a oil-bath gearbox to increase the wheel speed. Driven from an extension of the lathe countershaft the gearing allowed a work piece in the chuck to run at a modest 350 rpm whilst the grinding spindle rotated in the opposite direction at up to 12,000 rpm.
George Adams geared Toolpost Grinder - an expensive accessory at over half the price of the basic lathe.
GA 21/2F Precision Manufacturing Lathe. The Model F was supplied with a capstan unit mounted on the tailstock and a double-toolholder cross slide for forming and parting-off work.
The headstock was specially constructed to accept collets of a much greater-than-standard capacity - 11/16" in the nose and 9/16" pass-through - however, to achieve this within the confines of a 2.5" centre height and transmit enough power to make the enterprise worthwhile, the large-bore spindle had to run in such massive bearings that only a single wide pulley could be accommodated between them.
The Capstan tailstock that could be fitted to all GA 21/2 lathes. The barrel had a hole of unspecified taper into which a single tool could be inserted. A rotating stop provided an accurate depth location for each rotation of the handle - with the tool being automatically ejected at the end of the stroke.
The simple Forming and Parting Single Slide that attached to the cross slide of the compound rest.
The long-travel tool slides of the George Adams 21/2" Precision. Note, on this example, the raiser block under the headstock to increase capacity and the spacer at the front of the cross slide to increase its travel.
GA 21/2 plain-turning lathe on the maker's very light treadle and flywheel stand
With the compound slide rest fitted
GA车床型号212
造型精美的小乔治·亚当斯21/2“中心高精密车床已经成为业余机械师,特别是钟表匠们追捧的机器,热衷于获得真正的高品质产品(尽管必须说设计怪癖,几乎所有乔治·亚当斯的产品都出现在这个版本上)还发现了曼彻斯特和利物浦的R.Kelly,这个车床几乎可以肯定受到德国人Wolf Jahn练习的启发,这个练习的分数很小 - 通常是说只是“德国”,用小写字母表示 - 有时在公司的可识别的风格上印在不同的部件上,此外,配件也确认了这种连接,以相同的方式构造,可直接与Wolf Jahn原件互换。在翻转的形式下,21/2“也可以安装两种类型的螺纹切削装置:第一种是使用直接从换向轮到上滑块的直线轴这与正常使用键和万向节轴的做法不一致;第二个包括一个合适的床铺导螺杆 - 后者形式特别少见。从大约1900年到20世纪30年代中期,制造了几十年,它有一个典型的英式/德国模式的床,顶部平坦的头部,车厢和尾座由两个垂直平板剪刀形成的位置。一个不寻常的特征是床脚的安装 - 它们被简单地栓在铸件两端形成的相当难看的凸耳上。然而,在顶部和底部表面上的精密机器上 - 位于床的加工底面上 - 脚确实增加了床的刚度。
像所有的“精密”乔治·亚当斯车床一样,21/2“的车头架跟随着高质量的”台式车床*“的成熟模式,该车型的轴承由相对的硬锥体固定在主轴上或作为主轴的一部分,只要维持清洁的润滑油供应,这种轴承的使用寿命几乎是无限的 - 一些美国车床(斯塔克和韦德)成功吸收了五十多年的商业用途, (或称之为心轴)接受了一个硬化的,带有标准8 mm夹头的锥形刀片,顺便说一下,这个刀片很难被看到,在7/8“直径内非常紧密, 20 tpi的机头,如果需要使用完整的主轴孔,则必须拆除。
被设计成由圆形皮绳(或者流行的当代说法中的“肠”)驱动的3步铸铁皮带轮被锁定在主轴上是一种有些过度设计(尽管令人愉快)的夹头式方法,滑轮平行转动一小段距离,并开有四个等间隔的狭缝;一个大的夹紧环滑过开槽部分并用四个螺钉拧紧,直到它关闭到主轴上 - 下面的图片中可以清楚地看到布置。
同样整洁,虽然不是独特的 - 它也被Rivett雇用 - 是在长途旅行的复合滑轨上固定“平衡的”球头柄的方法;一个长螺钉,其开槽头部模制成与球的端部相融合,沿着横杆的杆向下穿过,与进给螺杆的端部接合。复合滑轨组件的设计是不寻常的,并纳入一些弱点;进给螺杆是25t.p.i.用黄铜千分表制成,在早期的例子中,用一个双圈和传统的“绳索”滚花,刻有0.002“的分度。多年来滑动休息改变了一些与机器的其余部分成比例预期的旅行长度),而其他显着不同的是相当长的交叉滑梯和更现代的千分表,但不幸的是,所有型号的滑梯至少有一个3英寸的运动,没有旋转设置的标记;同样令人失望的是,一台优质车床(尽管符合后来的Schaublin实践)是在尾座铸件上使用一个长的水平槽作为锁定(短)1号莫尔斯锥筒的夹具。铸件过紧和断裂的危险通过提供两个可调节的止动螺钉(在夹紧螺钉的两侧各一个)来减轻(在某种程度上)在下面的第三幅图中可以看到尾座缝隙的大小。
车床的配件种类非常多,可用于磨削,螺纹切削,精密锯切,铣削和轻型制造等工作。
乔治亚当斯车床上使用的原始颜色包括梅红色和翠绿色。
*包括:American Watch Tool公司,Arrow,B.C.Ames,Bausch&Lomb,Benson,Boley,Bott
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