Glad you are checking this out. You are correct in both cases. The chart on my lathe broke into pieces so I attempted to copy on an Excel spread sheet. I normally don't use the advance per revolution data so haven't paid attention to it. This was printed on an 8.5 x 11 sheet then reduced in size at a commercial copy/printing business to near the size found on the lathe. That in turn was laminated in plastic and pinned on the lathe.Also, there seems to be something amiss with the equivalent longitudinal feeds. For example, 16 TPI should be 0.0625 IPT or inches per spindle revolution. Not .008 inches per spindle revolution.
I wish I could help more and will if something else shows up. After thinking about Wa5cab's comment about the cutting feed distance per revolution of the spindle he is correct 1/16 is 0.0625 but my lathe has a rack and pinion under the front way and a set of gears in the apron that can power the pinion by a clutch assembly. The threads are dependent on engagement of the half nuts. If your lathe is like mine there is a plunger type knob that in the in position engages the cross feed lead screw and the outer position powers the carriage travel pinion. The half nuts can only be engaged with the plunger in mid (neutral) position. I will check tomorrow on the rack and pinion travel distance per spindle revolution and compare it to the chart to see if I can determine the gear ratio involved with the rack and pinion.I am the person that asked for a picture of a threading chart in a different post, so thanks for posting the spreadsheet. I am getting pretty close to having it all figured out between your spreadsheet and a couple of pictures from this site and other places. A really clear picture would help finish it all up. Thanks!
I am sorry about letting this thing get out of hand. What I found today was that the leadscrew turns 6.9444 time slower when cutting stock such as making a shaft (called long feeds on the chart) than when threading. The difference is in the gearing in the apron. I arrived at this number by measuring the carriage travel distance per spindle revolution then comparing that to 1/thread pitch. Most of the numbers were close if not right on. Several discrepancies were found due to what I think was rounding off. Nothing exceeded 5/10000 so I think the decimal numbers are usable. As I recall I copied the numbers without any calculation. I appreciate your time and efforts concerning this information.rock_breaker,
In the top row of your chart, shouldn't the 4th one from the left be 5.5 instead of 505 TPI? If so, I will correct it, convert the XLS to a PDF, and put the PDF in Downloads.