email: tony@lathes.co.uk
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"American" Pacemaker Lathes
The American Tool Works

Manuals & Parts Lists are available for these lathes

Although styled very distinctively in an amusing 1940s "Streamlined" way, the American Pacemaker lathes of 14-inch, 16-inch, 20-inch Medium Duty and 20-inch Heavy Duty, were no joke, but manufactured by the American Tool Works Company of Cincinnati, Ohio, USA to the very highest standards. All were very substantial machines; extremely well made, they boasted a specification that showed close regard had been paid to the needs of turners trying to extract the last ounce of performance from their machine. By the late 1940s cuttings tools and technology were developing rapidly and a need grew for even more rigid machine tools to take advantage of these improvements. After all, if the fellow in the works down the road could shift twice as much metal as you in a given time, with a better surface finish as well, it was pretty obvious who was going to go out of business first.
Made from a cast-iron mixture containing 40% steel scrap and other ingredients, which produced a semi-steel of approximately 40,000 pounds tensile strength, the bed had detachable V-ways, of solid tool-steel, hardened to approximately 60 Rockwell C, and ground to gauge tolerances for interchangeability with replacement units. After hardening, the metallurgical structure of the Vees was stabilised by cold treatment at minus 108 Fahrenheit for an eight-hour period to prevent twisting or warping. Four Vees were provided for the carriage and tailstock guides, the two inner Vees being dropped below the outer to provide a greater swing without the need to increase the thickness f the carriage bridge. An adjustable gib strip was positioned underneath the rearmost slide - and simple keeper plates at the front. In the maker's opinion, an all-V-way type bed was easier to keep clean and, consequently, offered greater resistance to wear than a flat one. It also, they claimed, wore more evenly than one using a combination of a Vees and flats  - but these were not conclusions shared by every machine-tool engineer, nor backed by rigorous research. The carriage ways were positively lubricated by a "one- shot", hand-operated oiling system built into the apron. One unusual refinement, found on some models, was a saddle fitted with hardened wiper plates; these were honed to fit the bed ways and so ensure that swarf was completely swept away and prevented from getting under the slide. 
A total of twenty-seven spindle speeds was offered as standard, in geometric progression, that divided into three ranges - low, intermediate and high. The low and intermediate ranges were driven through hardened spur gears, whilst the high-speed set was transmitted by wide-faced, 20-degree helical gears. All gears were finish-ground, except the large, slow-speed spindle gear on the 20-inch lathe that, owing to its size, was beyond the capacity of the maker's Pratt & Whitney gear-tooth grinders. Instead, this gear was finished on a "Michigan" cross-axis gear-lapping machine. If a customer wished to save money, or had no need of so many speeds, he could specify an 18 or even 9-speed headstock - with each available in low, medium or high-speed versions. The low-speed version hade a range from 15 to 1000 rpm, the medium from 23 to 1500 rpm and the high-speed from 30 to 2000 r.p.m. - the latter extraordinary fast for a large lathe. Stopping and starting a large machine tool effectively is always difficult and the Pacemaker was designed to make this as simple and reliable as possible. Mounted just inboard of the main drive pulley was a multi-plate clutch and powerful, multi-disc brake unit. These were contained within their own lubrication enclosure, each having hardened plates made from saw-blade steel running on ball and taper-roller bearings.
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Made from a hammered, high-tensile alloy-steel forging, the spindle rotated in large Timken Zero Precision Taper-Roller Bearings (of great expense) at the front and middle - and was allowed to "float" in a ball-race bearing at the rear.  In this type of spindle mounting the front and centre bearings were "opposed" to absorb spindle thrusts in either direction - and so eliminate the necessity for a thrust bearing, or thrust washers. The centre bearing also helped by supplying a rigid support for the spindle midway between the front and rear bearings - and so reduced deflection under the heaviest cutting loads. Lubrication was provided by a pump that forced filtered oil directly to the bearings and, conducted to the right places by a network of pipes, sprayed it onto the transmission gears, starting clutch and brake mechanism. Cleverly, although the oil supply was carried in the base of the headstock, it was positioned beneath the gear line to prevent churning and heating of the oil at high speeds. Both flow and level indicators were provided on the front of the headstock. Fitted with the then popular "American Long Nose key-drive taper the spindle nose was an L1 size for the three ordinary models and an L2 for the 20-inch Heavy Duty. However, a "Cam-lock" type could be supplied, if preferred by the customer. The removal of a small plate at the rear of the headstock gave access to a convenient means for adjusting the bearings. With the plate off a shaft was exposed which, when rotated, actuated a worm and worm wheel that in turn moved an adjusting collar. One turn of the adjusting shaft, which was self-locking, supplied a 0.001" adjustment to the bearings. The ease with which this could be done led the makers to suggest that the lathe operator himself could be encouraged to keep his spindle bearings in proper adjustment - an idea that might have gained acceptance if the chap doing the job knew what he is about. Unfortunately, if Fred "The Monkey Wrench" Johnson, the factory know-all turned up, the result might not have been quite that intended. The direction of the carriage movement could be reversed, without stopping the lathe or having to reverse the direction of rotation of the feed rod, by a lever operating a double bevel within the apron. Operation of the headstock clutch and spindle brake could also be controlled from the apron - as well as from the headstock.
Fitted with heat-treated gears, the double-walled apron had all shafts supported at both ends. The handwheel-operated gears that drove against the bed rack all ran on roller races, a design that helped to give the massive carriage a particularly easy and free-running feel, especially when chasing threads and attempting delicate work with a hand-driven traverse. The control levers for power sliding and surfacing feeds were on American Monarch (and English CVA) lines, with a powerful spring engaging a cone clutch on the power sliding and what the makers described as a "Safety angular tooth" on the cross feed. Both could be disengaged instantly by the cam action of the control lever, even when fully stressed under very heavy cuts. Should the feeds have been overload, the friction clutch on the longitudinal feed eased the drive whilst the cross-feed mechanism was designed to automatically disengage. The apron internals (and the bed and cross-slide ways) were lubricated by a plunger-type pump, one stroke of which provided enough oil for a whole day's working.
Designed to provide a long and reliable life thee cross-feed screw was hardened, fitted with ball thrust bearings, had a nut of the "compensating" type, adjustable for wear and the elimination of backlash and was equipped with an automatic oiling system. The direct-reading micrometer dials were of a reasonably large size, made in stainless steel and fitted with adjustable friction collars. Both slide gib strips were of the full-length taper type. adjustable from both ends. A rarely-fitted sophistication on any make was the provision of a "micrometer ball threading stop" as standard equipment on all Pacemaker lathes. At the end of each threading pass, the tool could be instantly withdrawn clear of the job (by up to three revolutions of the cross-feed screw) and the carriage wound back to its starting point. The tool could then be reset to its precise, original depth, and any additional cut put on before the screwcutting restarted. The device was mounted directly above the apron traverse handwheel, on a raised rectangular boss, and functioned in both forward and reverse directions. It could also, very handily, be used for both external and internal chasing operations or employed as a positive, single-diameter stop for duplicating diameters.
Of entirely conventional design, and supplied with a convenient one-shot lubrication system operated by a plunger, the screwcutting gearbox could generate 48 standard threads on the ordinary models and 60 on the 20-inch HD - without having to dismount or add any gears to the quadrant arm. Extra gears were available to cut metric, diametral and modular pitches and two special sets available to generate pitched of finer and coarser pitch than standard. The one useful thread missing from all the charts was 19 t.p.i. Used only to generate threads, the leadscrew was driven by a gear on power shaft that could be slid into and out of mesh by a small lever positioned where the shafts entered the gearbox on its right-hand side. The direction of the carriage movement could be reversed by a lever, operating a double bevel within the apron, without stopping the lathe or having to reverse the direction of rotation of the feed rod. Especially useful on the long-bed versions, it was also possible to control the spindle clutch brake from the apron as well as from the headstock.
A superbly designed and executed taper attachment was offered either as a plain version, with hardened steel guideways, or as a ball-bearing, anti-friction type. The plain-bearing version was essentially the same sturdy design as the anti-friction type, except that the Meehanite slides operated on hardened and ground steel ways with full-length Meehanite taper gibs for quick and easy adjustment. The makers claimed that this combination of materials reduced friction to a level that was almost the same as that of the anti-friction type - in which case the extra expense of the latter would not seem to have been justified.
The Ball Bearing Type was equipped with twenty-four permanently sealed anti-friction bearings - which could be adjusted for wear. Hardened and ground steel surfaces or "ways" were supplied for the anti-friction bearings, both in the sliding shoe and the bottom slide. These surfaces were extremely hard and kept clean by Duprene wipers, whilst all exposed surfaces were fitted with neat dirt guards..

The Electrical Switch Gear was mounted on the gearbox .

5-step V belt drive and screwcutting drive.

Ball-bearing Taper Turning Unit with some guards removed

The four bed Vs of the American Pacemaker

Compound slide rest

Headstock Bearing Adjustment Assembly

Apron mounted Longitudinal Feed Clutch and Lever Assembly

Headstock Input Pulley and Brake and Clutch Assembly

Rapid-feed assembly - fitted to the back of the bed

Rapid-feed assembly - end elevation

email: tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools Sale & Wanted
Machine Tool Manuals   Catalogues   Belts   Books  Accessories

"American" Pacemaker Lathes
The American Tool Works

Manuals & Parts Lists are available for these lathes