Alternative Charts for 8x14/9x30 Lathe
Threading and Power Feed Gears

Version 7 1/13/06
- got rid of lots of combos that did not work

Notes:
- The idea here was to find configurations such that
  the fewest number of gear changes are needed to
  switch from one to another. Emphasis is placed on
  standard choices for the inner gears. 
- The lathe includes just one of each gear size, but
  extra gears are readily available. Thus these charts
  call for 2 of some gears (as noted). 
- This was done using a small Perl program to search
  for candidate gear arrangements (code available). 
- Only 5-gear configurations were searched. This keeps
  the setup the same all the time. 
- The focus was on replacing only 2 to 3 outer gears,
  leaving Ti and Mi the same, and B too if possible. 
- Multiple banjos can be kept in the base configuration
  for inch threading, metric threading, and power feed
  modes. At some cost, this allows for faster switching.
- Metric gear configurations are chosen from among those
  with minimum deviation per revolution. 
- As noted below, the program also keeps the combined
  size of the two outer gears larger than that of the 
  two inner gears. This should avoid problems with 
  meshing. 
- Some of these are oddball sizes that you most likely
  won't run into, but I calculated some extras for
  completeness. 
- NOTE WELL: most of these configurations have not been
  tried and there may be problems with some of them
  meshing properly with each other or with the idler gear.
  If you find any to be in error or pose problems, or
  simply find a configuration that you think is better,
  please pass this information on to alan@yahoo.com.


Ti = top inside
To = top outside
Mi = middle inside
Mo = middle outside
B = bottom

note: To + Mo > Ti + Mi

R   = Ti/40 * Mo/To * B/Mi
TPI = 12 * R


Inch Chart (9-80)

emphasizes changing of To and Mo
this one has fewer dups
does not do low range
standardized on Ti=72, Mi=45, B=75
missing values means no 5-gear solution found


TPI	Ti	To	Mi	Mo	B	dups
-------------------------------------------------------
9	72	90	60*	45	50*
10      72	90	60*	50	50*	50
11	72	90	72*	66	50*	72
12      72	90	45	30	75
14      72	90	45	35	75
15      72	90	60*	50	75
16      72	90	45	40	75
18      72	80	45	40	75
20      72	90	45	50	75
22	72	90	72	66	100	72
24      72	90	45	60	75
25	72	72	45	50	75	72
27      72	80	45	60	75
28      72	90	45	70	75
30      72	72	45	60	75	72
32      72	90	45	80	75
33	72	72	45	66	75	72
34	72	72	45	68	75	72
35	72	72	45	70	75	72
36	72	80	45	80	75	80
40      72	72	45	80	75	72
42      72	60	45	70	75
45	72	72	45	90	75
48	72	60	45	80	75
50	72	72	45	100	75	72
54	72	60	45	90	75
56	72	48	45	80	70*
60	72	48	45	80	75
64	72	45	45	80	75	45
72	72	40	45	80	75
80	72	45	45	100	75	45


Metric Chart

standardized on Ti=72, Mi=45, B=75
some solutions are very inaccurate

pitch	Ti	To	Mi	Mo	B	dups
-------------------------------------------------------
.4	72	50	45	90	75
.5	72	50	45	70	75	
.6	72	60	45	70	75
.7	72	80	45	80	75	80
.75	72	70	45	66	75
.8	72	80	45	70	75
.9	72	90	45	70	75
1	72	70	45	50	75
1.25	72	90	45	50	75   
1.5	72	90	45	40	75
1.75	72	90	45	35	75	
2	72	90	45	30	75
2.5	72	100	45	30	75



To make a gear hob for lathes with metric gears of 
diametral pitch of 25.4, the tooth spacing is pi mm,
and the following combination approximates this:

3.14...	40	72	68	66	50


Power Feed ratios

Ratio	Ti	To	Mi	Mo	B	note
-------------------------------------------------------
16:1	75	35	30	90	100	std .005
17:1	80	30	35	90	100	no dups
20:1	80	30	30	90	100	2 @ 30
25:1	100	30	30	90	100	2 @ 100
32:1	80	25	25	100	100	2 @ 100,25
36:1	90	25	25	100	100	2 @ 100,25