Pat,
The Atlas 618 that you saw on eBay has an Atlas 10100 MK-II compound slide on it. The 618 originally came with the same compound slide and cross slide as the 101.07301.
For some unknown reason, dating all the way back to the first 9" in 1932, Sears has always ordered different legs on the 9", 12" and 6" that Atlas built for them. The majority of the other parts are the same as whatever Atlas was currently supplying on their 9", 10" or 6".
Yes, your machine is a 6x18 but not a 618. Up until the 10F came out and they changed their model number assignment system, the model numbers were made up from numbers that describe the size of the lathe. Up through the 10D and 10E, all model numbers began with the one or two-digit swing, followed usually by the bed length. So a 1036 would be a 10: with a 36" bed. A 1054 is the same lathe but with a 54" bed. Exceptions were the 918, 612 and 618 where the first digit is the swing and the second digit was the distance between centers. The reason for doing that with the 918 was that the 936 number was already used for the 36" bed compound drive machine. The 918 was the simpler and cheaper utility lathe with no compound drive and no back gears. Why they chose to do it with the 612 and 618 no one knows.
The 618, with Timken bearings and back gears, came out in 1937 (catalog year, probably printed late in 1936). It had the first version countershaft with the bracket swung off of the rear of the headstock. The first 6" lathe that Atlas built for Sears, the 101.07300, came out in 1938. It had a smaller spindle with 3/4"-16 threads, 1MT taper and sleeve bearings. And no back gears. Most of the other parts were the same as on the current 618. The following year, Atlas revised the countershaft on the 618 and started building the 101.07301 for Sears. It now had 1"-8 threads and 2MTspindle taper. Most parts on the 101.07301 are the same as those used on the 618. Exceptions, besides the legs, were the headstock casting, spindle, and spindle thrust bearing, all because of the sleeve bearings. All other parts were the same. Around 1940, Atlas revised the countershaft assembly on the 618 but continued to supply what was the second 618 version on the 101.07301 up through end of production in 1957. A fair number of 101.07301's have had the countershaft assembly replaced with the third version 618 unit. The notable differences between the 2nd and 3rd version countershaft assemblies are that the newer compound bracket is taller and curved, and the pulleys hang down below the bracket, instead of sticking up above it.
