First shown in the All-models catalog for 1931/1932, Atlas drill presses were eventually to be branded - as were many of the company's other products - as "Craftsman" and "Dunlap" for sale by Sears. The drills were introduced as a range of three models: from a light, plain-bearings type, the No. 40 for amateur use, to a pair of better-specified, heavier and greater capacity versions, the Nos. 50 and 60. The latter, more expensive pair - intended for use in small engineering shops and industrial and automobile repair workshops - had spindles and pulleys supported in easily-changed ball races that could be run continuously at high-speed. Between their introduction and 1940, Atlas drills - like the company's lathes - enjoyed a steady stream of modifications that made them heavier, more rigid and with better thought-out speed ranges. Despite years of hard use and neglect, a surprising number of these drills presses survive in good working order and, correctly set up, run smoothly and quietly - in contrast to the horrify noises and vibrations than emanate from many of today's equivalents, those cheap and nasty ones made in the Far East.
The first Atlas drills all shared one common feature: a relatively light head casting that socketed onto, or around, a steel column with the other end in the form of a fork bored to accept the quill and front pulley. Instead of being enclosed within the head, the quill (the element that held the rotating spindle) was completely open, the makers proclaiming an advantage for this skeletal construction by claiming: "Atlas Open Head provides utmost in accessibility for lubrication and adjustment". That may have been so, but it did absolutely nothing for rigidity…
At $13.95 minus a motor, the least expensive offering was 65 lb Model 40; this had a 1.5-inch diameter ground-steel tubular column upon which sat a cast-iron head holding a 5/8" diameter spindle. With 3" of travel, and guided by a single keyway, the spindle was held inside a quill assembly and ran in plain "Oilless" bronze bearings. From the beginning, 4-step V-pulleys in Zamak were employed on all models - that at the front on the Model 40 being covered by a cast-iron guard and its mounting shaft turning in the same type of plain bearing as used for the spindle. Drive came from a motor fastened either to a plate at the back of the head, or with the drill's foot plate swivelled to the rear, bolted to that and with a pair of jockey pulleys used to turn the drive through 90°. Ingeniously, the head-mount motor was carried on a platform that could be raised and lowered: hence, while the four normal speeds were obtained by swapping the belt between pulleys with the plate in its middle position, by raising and lowering it a further set of four combinations could be achieved. The result (using a 1725 r.p.m. motor) was a range of 8 speeds that spanned a rather fast but useful 1000 to 3000 r.p.m.  The foot-mounted drive - a very old-fashioned arrangement, even for 1931 - was intended (presumably) to allow an impecunious amateur the opportunity to use one motor, with additional pulleys and shafts, to drive a variety of other machines mounted together on one bench.
Just 7.5" x 7.5", the table could be swivelled through 360° and had locking points in the horizontal and left and right 90° positions. The maximum clearance from table to chuck jaws was 9 inches - this being the absolute maximum as, very oddly, there was no flat machined surface on the foot, just an opening with the sides rails slotted to take the optional motor mount. The Model 40 was to morph first into the Model 41 and the, finally, the Model 42, in which guise it survived (price at $18) until 1941 - but did not reappear after WW2.
A rather better engineered job, (at $22.45 without a motor), was the 85 lb Model 50. Constructed along the same basic lines of the Model 40, this drill was made more suitable for commercial use by both the spindle and front V-pulley running in ball races. The ground-finished steel column was 17/8" in diameter and carried a 8" x 9" table able to be swivelled through 360° - locking points being provided in the horizontal and left and right 90° positions. The maximum clearance from table to chuck jaws was a much more useful 11" and, as the base was machined flat, an additional 4.5" of clearance was available to accommodate taller jobs. With its motor carried on a plate that could be adjusted in and out to set the belt tension, the 4-step Zamak pulleys - in combination with the raising and lowering mechanism of the drive unit - gave nine speeds that ranged from 600 to 4000 r.p.m. Also available was a version fitted with jockey pulleys that allowed a bench-mounted motor to be used - though in this case, as the drill's mounting foot was machined and intended to be used in the conventional forwards pointing position, it had to be bolted to the bench itself.
Top of the Atlas drill range for 1931 to 1932 was the $28.75, 105 lb bench-mount Model 60 - and its otherwise identical partner, the 155 lb floor-standing Model 70. Equipped with a 2.75-inch diameter, ground steel column, each model carried a 10" x 10" table that, as on all other Atlas drills, could to be swivelled through 360° with locking points provided in the horizontal and left and right 90° positions. Although the head used the same rather light construction of the cheaper versions (and with the same vertically adjusted motor mount), the design was beefed up and the front pulley carried in two ball races rather than just one. Fitted with a standard 0.3 h.p. 1725 r.p.m. motor, nine speeds were available, these spanning 600 to 4000 r.p.m. Oddly, even this most expensive version could be had with jockey pulleys for drive from a bench-mounted motor - though sales of this type must, surely, have been insignificant.
As with their lathes, Atlas offered a range of accessories, the first catalog listing the expected sets of drill bits, router and countersink cutters, two machine vises, a mortising attachment, a drum sander, and a "shaping" attachment. The latter, consisting of an auxiliary table and fittings, an adjustable shaper fence, spring steel hold-downs (and various cutters) could be employed with head in either the normal position or - making it much like a conventional wood "shaper" - inverted on the column with the spindle end protruding through the centre of the table.
The following links show how the drills developed during the 1930s until, by 1940s, almost the final form had been reached - the Models 63 and 73 with these looking almost modern and available with a much safer, fully enclosed head.  The range of accessories was also expanded with additional items including the clever "HI-LO" speed attachment, a quick-change belt release mechanism, tapping units, tap holders, foot-lever control, oil-pan tables, coolant equipment, full enclosure safety belt guards, light unit, column support collars, a Universal Compound Table with built-in vice, Morse taper spindles, a vernier engraved depth stop, a drill-grinding attachment and, for the 60 and 70 Series (and later, larger models), a screw-feed head and table positioning system and a radial-arm assemble to cantilever the head out from the column. One very unusual accessory, the Oscillating Sander Attachment, was to make a single appearance in the catalog for 1941

1933/36 Models 41, 51, 61 and 71   
1937/38 Models 42, 52, 62 and 72   
1939 Models 42, 52, 63 and 73   
1940s Models 42, 52, 63 and 73
1950s Models 1020, 1040, 10,25, 1045, 1400, 1410, 1405, 1415, 1060, 1080, 1065, 1085, 1420, 1430, 1425 and 1435

What year is my drill? Links to the pages above and a close study of the illustrations will give you a close idea. However, old stock would almost certainly have been sold on into the following year (or even years) - and newer versions could well have been on the market before the catalogs were issued. Hence, to avoid the wrath of the pedants, a drill is best dated from its appearance in the catalog, not when it was sold. e.g. A 1939 Model might well have survived with its original invoice dated 1941, but it's still a 1939 type….