A  well-thought-out, strongly-made machine, the Clausing horizontal miller had a stiffly-braced, one-piece cast iron column that carried twin, solid-steel bars to act as the horizontal arbor support. The alloy-steel spindle, with a hardened 30 A.S.A. (International) taper nose, ran in lubricated-for life 3.5" diameter Timken taper roller bearings and carried a helical, lathe-like "backgear" assembly (running in an oil bath) that multiplied the torque available by approximately 6 and provided a slip-free, high-torque drive to the slower speeds. Clausing guaranteed a better than a one-half thousandth of an inch run-out on the spindle that was bored through 21/32" and used a 21/32" x 13 t.p.i draw bar. A choice of three arbor diameters was offered: 7/8", 1" and 1-1/4"
An expanding-and-contracting infinitely-variable speed pulley drive system was fitted (driven by a 1.5 hp single or three-phase motor) with the rotary speed selector (which operated a hydraulic change mechanism) marked off to show 12 speeds from 52 to 280 in "backgear" and 360 to 2000 rpm in direct belt drive. The final drive from the top variable-speed pulley shaft to the spindle was by 3 V belts - a better solution than using two where any slight difference in their length could have caused catastrophic vibrations to be set up.
Ground-finished, the 26.125" x 6.76" table was provided 3 T slots and had a longitudinal travel of 17.25",  a traverse of 5" and  a vertical movement of 14".  Like the maker's  8530 vertical miller a hand-operated fast table feed was fitted; the unit consisted of a gearbox hung from the end of the table with a feed handle permanently attached to a lower shaft that connected directly into the reduction gearing. With the handle pushed in the feed screw was driven at a 1:1 ratio but when pulled out a "high-speed" 4 : 1 drive was engaged where one turn of the handle rotated the feed screw through 4 turns to re-position the table very much more quickly.
A well designed optional power feed attachment was also available; this reduced the longitudinal travel to 15.375" but gave 12 rates of power feed from 0.44" through 0.62", 0.85", 1.06", 1.32", 1.86", 2.55", 3.18", 3.96", 5.58", 7.65" to 9.54" per minute with automatic knock-off and protection by an overload clutch; feed rates were changed by rotary selectors on the side of a column-mounted table-feed gearbox that drove, though a universal shaft, to a reversing and engagement gearbox fastened to the knee underneath the table.  A rotary dial on the reversing box selected left or right movement whilst a lever enabled the drive to be flicked in and out of mesh. The table feed screws were ground finished, ran through ball races in the supporting end brackets and were fitted with large, satin-chrome finished micrometer dials.
Four models were offered:
No. 8541 1-phase main motor, power table feed
No. 8551 1-phase main motor, hand table feed
No. 8540 3-phase main motor, power table feed
No. 8550 3-phase main motor, hand table feed.
Approximate dimensions were: width 59" (including table travel), depth (with guard clearance) 46" and height 56"..
One rare model was the 8513, a factory special that used the popular Bridge Type M head in place of the regular Clausing unit..

The alloy-steel spindle ran in lubricated-for life 3.5" diameter Timken taper roller bearings and carried a helical-gear, lathe-like "backgear" assembly (running in an oil bath) that multiplied the torque available by approximately 6 times and provided slip-free slow speeds. 

The hydraulic pipe connecting the speed-change knob and the actuator on the end of the motor's expanding and contracting pulley can be clearly seen in this illustration.

The drive from the table feed gearbox was taken by a universally-jointed shaft to a reversing gearbox fastened to the knee underneath the table. A rotary dial selected left or right movement whilst a lever engaged and disengaged the drive.