Joe,
The Craftsman (Atlas) 12" machines were built from sometime in 1936 through 06 March 1981. Up to a date in either 1957 or 1958 (no one seems to have a 1958 Craftsman Power Tools catalog to settle the year), the ways were 3/8" thick and the nameplates are on the rear of the bed toward the right (tailstock) end. From that date until end of production in 1981 the ways are 1/2" thick and the nameplates are on the right end of the bed below the ways. And also from that date, Atlas (or Clausing) also sold the same machines with Atlas badges and model numbers.
The only way I know of to approximately date a babit bearing headstock model (absent the original sales paperwork) is by comparison to photos and specs in the late 1930's and early 1940's catalogs. Timken bearing equipped models that still have their original bearings have a date engraved on the bearings. The date is actually the bearing inspection date but can be assumed to be within a month or two of the machine finish date. The 1/2" bed models have a casting date cast into the rear face of the bed casting. However, on my Atlas 3996 (made 1980), the date cannot be read.
If the nameplate is missing, the model can be roughly determined by comparing the machine's characteristics to those listed or shown in photographs in the catalogs. For example (assuming of course that the machine hasn't been modified or upgraded since production), power cross-feed or not, bed thickness, headstock casting shape, lead-screw diameter, bearing type, tailstock part number, belt and gear cover shape, etc.
Very early machines were sold incomplete with some of what today we would assume would be present available as extra cost options, such as the carriage, lead screw and carriage drive gearing and other components, belt guards, etc. No one seems to know what model numbers those machines carry.
From 1936 or 37 to 1951, there were 12 models sold relatively complete that I know of. However, two or sometimes three models would be available in a given year. So the model number sequence from 101.07360 to 101.07403 is not strictly chronological. And to add further confusion, the model number up through 101.07403 does not specify the bed length. For that, you had to refer back to the Sears catalog number. From 1951 on, the model number also specifies the bed length (except for the 101.07403 which remained in production through 1957).
There is a QCGB first produced 1951 that will fit all 12 early models. And a later one that only fits the 1/2" bed machines. Many of the parts in the two models are the same but the main castings are not. The two can be identified from photographs by the shape of the handles on the selector levers (if the handles are original to the box).
Robert D.
