All purveyors of old machinery stories are welcome here, embellishment is encouraged!!
I believe you are describing changes to the apron and saddle in the lathe series revisions.
The "Orginal Series" or as I call it the "O'brien Series", listed in the parts and catalogs as the
"O" Series was first designed by the "O'brien Twins" (note the "Twins" logo on the big S brass tags) after several years of revisions and started production in 1906 as the South Bend Machine Co. Through the years with design improvements South Bend separated the "O" series into, what they called internally, Group 1, 2 and 3. Without their later revised Serial Number system (started in 1947) and the major revision unit code tracking system (stared in 1930/31) that made it a daunting task to track models, revisions and catalog numbers by manual entry. After 30 (Group 1, 2, 3
years, the "O" series needed some major revisions and with the depression causing devastation, they forged ahead to complete the improvements. Their revisions were completed in a build unit or assembly, like you see in the later parts manuals. Headstocks, apron, saddles and so on...
Here is the old system of recording the serial number ship date an info in the leger books, keep in mind they were all "O" series lathes.
This is hand copied typed card from the old ledge book for an O series 9-inch Junior like yours.
The sale date is the approximant time period that the unit code system was started and the Serial Number card system listing unit code info and much more was started.
And this is the time frame of the basic card system in place, showing mostly unit codes number 1, which is first design (they later added a revision number to these unit codes, like H101, headstock 1st design, first revision or 102, first design, 2nd revision. when a major casting change was made the design number changed...H201,H 202.
South Bend and the twins were very good at organization, improvement, and cost analysis.
The made design changes on the smaller lathes first to save on casting and machining costs.
When they had completed a unit design change, they then worked up the sizes to complete a new series of lathes. The first new letter series lathes were the N Series, starting production in 1931. The Series N had a new ("N") double wall apron and saddle with tapered gibbs.
On this card, you can see the design changes (7) stacking up on the Headstock and other unit codes. Note the 1934 ship date, this lathe was built in 1932, depression related no doubt.
And the question on the modern shifter apron. That apron was introduced in 1934 on the Next Series "R" (Revised Apron), it did not however have tapered gibbs when first introduced.
They had been working on this series for 3 years also and it would replace the N series apron eventually.
Here is a rare lathe, that proves this, a 1931 Series R with the new apron.
In the mid to later 30's the new saddle casting with tapered gibbs were added to all Series. When the new saddle and new apron with other improvements were completed across all sizes, they introduced this completed change over as the Series T lathe (Tapered Gibbs).
Here is an interesting card, a Series R, 9-inch, that was returned to South Bend from consignment, rebuilt as a Series T lathe and shipped out again for the war effort no doubt.
http://www.wswells.com/sn/sn_cards/sc_72157.pdf
The last of the Letter Series Lathe is the Series S (Speed lathe) all prior improvements plus a new headstock and other goodies. it lasted until they closed the plant, if you include the rebuild shop. The oldest Series S lathe I've recorded is 1938 date, SN 86353. It would have had 100's on the unit codes, that would be cool to see, and if the owner of this lathe is reading, I'll pay for your card for you if you want it.
This one is newer, and shows revision numbers, maybe they replaced the wooden holders for headstock spindle oilers...LOL...BEFORE they released the Heavy Ten.
Ok, I hope you enjoyed this long-winded post with excerpts from my unfinished, unpublished book!..haha