Smithy Midas 1220 XL - Manual (Page 76)

15.3 Using a center gauge, set the threading tool at exactly dead center on the workpiece.
Cutting Right Hand Threads
Now you are ready to cut right-hand threads, First, advance the tool so it just touches
the workpiece and turn the compound calibration back to zero. Then, using the
compound feed, feed in the tool 0.002”. Next, turn on the lathe and engage the half-nut
lever by carefully turning it one-quarter turn to the right. Do not force it, and do no
disengage I until you are completely done.
It is best to take a light, scratch cut first without using cutting fluid. After the tool runs
the desired length, turn off the lathe and back the tool out of the work. Then reverse the
motor to return the tool to the starting position. Using a screw-pitch gauge, check the
thread pitch. The benefit of taking the light cuts is that you can correct any mistakes you
might have made.
It’s time to take the real cut now, so apply the appropriate cutting fluid to the workpiece.
Feed the cross slide in 0.005-0.020” for the first run, depending on the pitch of the thread
you have to cut. If you are cutting a coarse thread, start by taking a few heavy cuts.
Reduce the cut depth for each run until it is about 0.002” at the final run. Zero the
cross-feed calibration and make the second cut.
Continue this process until the tool is within 0.010” of the finished depth. Brush the
threads regularly to remove chips. After the second cut, check the thread fit using a ring
gauge, a standard nut or mating part, or a screw-thread micrometer. It is best to leave
the workpiece in the chuck and not to remove it for testing.
After returning the workpiece to the setup, continue taking 0.00-0.002” cuts, checking the
fit between cuts. When you thread the nut, it should go on easily but without end play.
When you have the desired fit, chamfer the end of the thread (that is, take 45 degree cut
off the end) to protect it from damage, Figure 15.4.
Workpiece
Toolbit
Center
Gauge
15-3
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Midas 1220 XL Operator’s Manual