NOTICE
The threading dial cannot be used when cut- ting metric threads. Once the half nut has been engaged, it must remain engaged throughout the threading process.
Half Nut Lever - This lever compresses and releases the half nut that engages the leadscrew. See Figure 16. The lever is only engaged while turning threads in stock. A lockout device fea- tured in the lever mechanism engages when the feed selector is used.
NOTICE
Do not simultaneously engage the feed lever and the threading lever. Doing so will damage the lathe.
Dial
Lever 
Figure 16. Threading dial and half nut lever.
Threading Dial Indicator - The indicator tells you when to engage the half nut to begin the threading process. See Figure 16.
The Threading Dial Indicator has 8 lines and four numbers printed on the dial. An indicator mark is positioned near the rim of the dial. The dial is mounted on a shaft that has a worm gear mount- ed at its opposite end.
These rest in a housing that pivots so that the gear can be engaged or disengaged. An Allen® head cap screw is located on the side of the housing. Loosen this screw to change the posi- tioning of this housing.
When engaged, the dial will turn when the spin- dle is turning. If the dial does not turn, readjust the housing.
When the half nut is engaged the dial stops turn- ing. By carefully engaging the half nut as the appropriate line or number passes by the indica- tor mark, a thread can be established and the lead maintained through the multiple passes that are required to cut a thread to the finished depth.
The chart listed in Figure 16b shows a system for using the threading dial indicator while cutting inch threads.
Example:
To cut 11 threads per inch engage the half nut when the 1 or the 3 is on the indicator mark. Determine the length of the thread to be cut. Make a cut along the part and disengage the half nut. Return the carriage to the beginning of the cut. Watch the dial and when the 1 or the 3 comes around to the indicator mark engage the half nut. Repeat this process until the desired depth of cut has been achieved.
16b. Dial indicator chart.
G4002/3 Gear Head Lathes |