Smithy Midas 1220 XL, Operator'S Manual

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Gear Ratios
The lathe lets you use various indicated gear combinations to cut the desired number of
threads per inch (tpi), or the metric equivalent, or to advance the tool at a specified
amount each revolution (feed rate expressed as inches per revolution (ipr))
The Midas 1220 XL has a pick-gear gearbox (Figure 5.2); gears are picked and placed to
change the gear ratios. The gearbox mechanism determines the leadscrew's rotation rate
in relation to the spindle's for threading, turning and facing. To change the thread pitch
(tpi), replace the gears per Table 7.2.
Table 7.2 Gear Ratios
Threads Per Inch Metric Pitches
1 2 A B C D
.003 .006 30 60 27 63
30 15 70 32 40 45
28 14 70 32 40 42
26 13 70 32 40 39
24 12 70 32 40 36
22 11 70 32 40 33
20 10 70 32 40 30
18 9 70 27 45 36
16 8 70 27 45 32
14 7 60 27 60 32
12 6 70 27 60 32
A
B
C
D
E
MM
Speeds Gear Position Speeds Gear Position
1 2 A B C D
0.50 1.00 49 32 42 56
0.60 49 32 45 50
0.70 49 32 42 40
0.75 1.50 63 32 42 48
0.80 49 50 60 32
1.75 49 48 63 32
1.00 2.00 63 32 49 42
1.25 2.50 60 32 49 32
1.50 3.00 63 32 56 32
7-3
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