By the late 1940s cuttings tools and technology were developing rapidly and a need grew for rigid machine tools to take advantage of these improvements. If the fellow in the works down the road could shift twice as much metal in a given time as you, with a better surface finish as well, it was pretty obvious who was going to go out of business first.
The headstock of the  "American" Pacemaker lathe had twenty-seven spindle speeds, in geometric progression, which could be divided into three ranges - a low,  intermediate and high. The low and intermediate ranges were secured through hardened spur gears, while the high-speed range was transmitted by wide-faced, 20 degree helical gears. All gears were finish ground, except the large, slow-speed spindle gear on the 20" lathe which, owing to its size, was beyond the capacity of the maker's Pratt & Whitney gear tooth grinders. Instead this gear was finished lapped on a "Michigan" Cross Axis gear-lapping machine.
The customer could specify 27 or, at a saving in cost, 18-speed and 9-speed headstocks - and each type was available in Low, Medium or High-speed versions. The Low-speed specification ranged from 15 to 1000 rpm, the Medium from 23 to 1500 rpm and the High-speed from 30 to 2000 rpm.
Just inboard of the main drive pulley, and mounted externally to the headstock in their own unit, were a multi-plate clutch and a powerful, multi-plate brake, each having hardened plates made from saw-blade steel running on ball and taper-roller bearings and lubricated by a pumped oil supply.

The spindle was a hammered, high-tensile alloy-steel forging which rotated in large Timken Zero Precision Taper-Roller Bearings at its front and at its centre - 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 eliminated the necessity for a thrust bearing, or thrust washers at the end of the spindle. 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.
On the Pacemaker the removal of a small plate at the rear of the head gave access to a convenient means for adjusting the Timken spindle bearings. With the plate off a shaft was exposed which, when rotated, actuated a worm and worm wheel which 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 could be encouraged to keep his spindle bearings in proper adjustment - which would have been fine if the chap doing the job knew what he is about, but if Fred "Monkey Wrench" Johnson, the factory know-all turned up, the result might not have been quite that intended ………….
The spindle nose was fitted with the (by then) popular "standard key-drive taper nose", in an L1 size for the 14" , 16" and 20" lathes and an L2 for the 20" Heavy Duty. A cam-lock type of nose could be supplied if preferred by the customer.

A stripped headstock casting showing the oil pipes though which the entire assembly was lubricated by filtered, pumped oil forced directly to the bearings, and sprayed onto the transmission gears, starting clutch and brake mechanism. The oil supply was carried in the base of the headstock, below the gear line to prevent churning and heating of the oil by the gears at high speeds. Flow and level indicators were provided on the front of the headstock.