Metric Threadcutting gears for antique South Bend lathe

[bobneumann]

Here's how the spreadsheet works:

1. You need to know the toothcount for your factory stud gear. Mine is 24.
2. You need to be able to read the chart on your QC gearbox, becuase you'll need to know the full list of threads that your lathe is capable of.

Instructions:
1. In field "F1" enter the number of teeth on your factory stud gear.
Example: Single Tumbler Heavy 10 stud gear is 24 teeth.

2. In Fields G3 down to G46 (or farther down as necessary) enter the exact TPI values that your gearbox is capable of
Example: Single-Tumbler Heavy 10 can do 42 unique TPI settings ranging from 4 TPI to 224 TPI
3. For a given metric pitch, visually search in the green "resulting metric pitch" field for the value nearest to the desired metric pitch, then pick the closest match for the replacement stud gears that you have to work with.
Example: For a desired metric pitch of "7", the nearest stud gear/qc setting would be a 33Tooth stud gear with a QC Setting of "5", resulting in a perfectly acceptable metric pitch of 6.985

4. Fill out the chart for all the values for your lathe, selecting for the fewest number of gears that need to be made.
As downloaded, the chart is pre-filled out for a lathe with a 24T stud gear, and a SouthBend single tumbler gearbox.
The best selection of stud gears for that 24T/single tumbler lathe turns out to be 19,26,33,34, and 37 tooth stud gears, which can create all common metric fasteners under about 50mm.