Threading Change Gears, Precision Matthews PM-1228VF-LB Lathe by wt808

Last crawled date: 3 years, 1 month ago

36-, 39-, and 40-tooth gears that provide additional Imperial and Metric threading capabilities for the Precision Matthews PM-1228VF-LB Lathe. These gears should also fit the Grizzly G0773 lathe/mill and Sieg SC10 lathe.
The PM-1228 comes with 5 gears (30, 35, 49, 50, and 60T) that can be installed at the position marked "G" on the label/manual diagram, and a 56T gear that can be installed in place of the 86T gear.
The 36T gear installed at G provides the following threading capabilities.
Imperial (36, 91, and 90T gears meshed in line, tpi):

Lever A B C
1 60* 30* 15*
4 40 20 10
Metric (36T meshed with 91T, 90T meshed with 86T gear, mm):

Lever A B
1 0.4* 0.8*
2 0.45* 0.9*
4 0.6
The 40T gear installed at G provides the following threading capabilities.
Imperial (40, 91, and 90T gears meshed in line, tpi):

Lever A B C
1 54* 27*
2 48 24 12
3 42* 21*
4 36 18 9
5 30* 15*
Metric (40T meshed with 91T, 90T meshed with 86T gear, mm):

Lever A B C
2 0.5 1 2
5 0.8*
The 39T gear installed at G plus the 56T gear in place of the 86T gear provides the following threading capabilities. Before turning on the lathe, verify that there is no interference between arm 857 and gear 855. There should be roughly 1-2mm of space between them so that the gear rotates freely.
Imperial (39T meshed with 91T, 90T meshed with 56T gear, tpi):

Lever A B C
1 90* 45*
2 80* 40 20
3 70* 35*
4 60* 30* 15*
5 50* 25*
Notes:
A 27T gear at G would provide 80tpi and 0.3mm, but the gear is too small and there is not enough material around the keyway. The 39T gear combination can produce an 80tpi thread.
Installing the 30T gear at G plus the 56T gear in place of the 86T gear would provide the following threading capabilities, but this combination is not possible because arm 857 interferes with gear 855. The 39T is the smallest usable gear without interference.
Imperial (30T meshed with 91T, 90T meshed with 56T gear, tpi):
Lever A B C
1 117*
2 104* 52* 26
3 91*
4 78* 39*
5 65*
Values noted with an asterisk (*) are threads not previously available using the factory-supplied change gears.