CHANGING GEARS FOR SCREW CUTTING
The lead screw is driven via a gear train and a gear on the spindle. The gear ratio will determine the rotational speed of the lead screw with relation to
the spindle, i.e., one turn of the spindle will turn the lead screw an amount determined by the gear ratio.
By setting the gears to a known ratio, we can therefore produce threads of a known size, and as the lead screw supplied produces Imperial threads,
the known values will be in Threads Per Inch (TPI).
As previously mentioned, the actual thread produced will be totally dependent upon the profile of the cutting tool. It is not within the scope of this
manual to provide detailed information regarding types of cutting tool, cutting speeds and working with various types of material etc, and it is strongly
advised that you consult appropriate handbooks or seek advice from a qualified person.
The chart below shows the thread sizes that may be cut using the gear
configuration shown in the corresponding columns.
NOTE: The factory setup for the lathe provides for normal turning
using the power or auto feed, and the gear configuration is as follows:
Gear A 20T; Gear B 80T; Gear C 20T, Gear D 80T.
In order to change
the gears, ensure the
machine is switched
OFF and disconnected
from the wall outlet.
Remove the gear train
cover which is secured
with two socket head
screws.
Gear A may be
considered as the
driver, and gear D
as the driven gear.
When a simple gear
train is configured, as
illustrated in fig. 9, gear
B acts as an idler and
its size is therefore irrelevant – any convenient gear will
suffice to connect A and D. This is denoted by a blank space in the
column in the gear chart.
The positions of the shafts carrying gears A and D are fixed;
therefore, all adjustments are carried out on the shaft carrying gears
B and C and the adjuster “A”, shown in fig. 9.
1. Unscrew the hex socket head screws securing gears A and D,
followed by the screw securing gears B and C.
2. To allow the gears B and C to disengage completely and to
provide for easier reassembly, unscrew the nut securing the
shaft carrying B and C and the nut securing the adjuster A.
3. Remove the gears, taking care to retain the small keys on each
shaft, and replace with those necessary to produce your screw
thread. They may be mounted either way round. The number of
teeth on each gear is clearly marked. Replace the securing
screws, ensuring the flat washer bears up against the gear hub
in each case.
NOTE: If a compound gear train is required (B), ensure the spacer,
which is keyed to the shaft carrying gear D, is located on the shaft
BEFORE the gear, in order to align gear D with gear C.
4. Proceed to move the shaft carrying B and C and the adjuster
“A” so that all gears mesh correctly, then tighten the adjuster
securing nuts. This may take one or two attempts, but make
sure there is as little backlash as possible without being
over-tight (turn the spindle by hand to test for backlash).
Replace the cover and secure with the two hex socket head bolts.
Threads
Gear
Per Inch
A
B
C
D
12
40
30
13
40
65
60
30
14
40
35
16
40
40
18
40
45
19
40
50
60
57
20
40
50
22
40
55
24
40
60
26
40
65
28
20
35
32
20
40
36
20
45
38
20
50
60
57
40
20
50
44
20
55
48
20
60
52
20
65
Examples:
1. Fig. A
To cut 12 TPI, use
40T in position A,
30T in position D
and any convenient
gear in position B to
connect A and D.
GEAR CHART FOR CUTTING IMPERIAL THREADS
9
Spindle
A
B/C
D
2. Ref. Fig. B
To cut 13 TPI, use
40T in position A,
65T in position B
60T in position C
30T in position D
10
Fig. A
Fig. B
