Change gear charts for a basic Smithy.  This zip file contains four files:

smithy-change-gears-readme.txt -- this file
smithy-change-gears.pdf        -- PDF rendition of the change gear tables
smithy-change-gears.tex        -- LaTeX file, that makes the PDF file
smithy-changeGears.sci         -- Scilab executable, generates the tables

This is based on a Smithy with a 10 TPI pitch lead screw, and a gear box 
that (apparently!) has a 6:35 or 12:35 ratio from the spindle to its output 
gear teeth.  The thing has a two-speed gear in the spindle box, then a
four gear set that Smithy labels A, B, C and D.  The A and C gears divide
the effective ratio to the leadscrew, while the B and D gears multiply.

To adapt this to a Smithy that uses the same technique with different gears,
change the 'gears' array in the 'allChangeGears' function.  Use the 
'changeGears' function to find the closest fit to a given pitch (in 
inches -- i.e. for 20TPI set pitch to .05).  Use the 'changeGearTable'
function to generate the above LaTeX document.