Lincoln Electric LTW1 - Manual (Page 11)

10 LEARNING TO WELD 10
3. The Contact Tip to Work Distance (CTWD)
The Contact Tip to Work Distance (CTWD) is the
distance from the end of the contact tip to the work.
See Figure 18.
Once the arc has been established, maintaining
the correct CTWD becomes extremely important.
The CTWD should be approximately 3/8 to 1/2 inch
(10 to 12 mm) long.
The easiest way to tell whether the CTWD is the
correct length is by listening to its sound. The cor-
rect CTWD has a distinctive
“ crackling ” sound, very
much like eggs frying in a pan. A long CTWD has a
hollow, blowing or hissing sound. If the CTWD is
too short, you may stick the contact tip or nozzle to
the weld puddle and/or fuse the wire to the contact
tip.
FIGURE 18
4. The Correct Welding Speed
The important thing to watch while welding is the
puddle of molten metal right behind the arc. See
Figure 19. Do not watch the arc itself. It is the
appearance of the puddle and the ridge where the
molten Puddle solidifies that indicates correct weld-
ing speed. The ridge should be approximately 3/8
”
(10 mm) behind the wire electrode.
Most beginners tend to weld too fast, resulting in a
thin, uneven,
“ wormy ” looking bead. They are not
watching the molten metal.
FIGURE 19
Helpful Hints
1. For general welding, it is not necessary to weave
the arc, neither forward or backward nor sideways.
Weld along at a steady pace. You will find it easier.
2. When welding on thin plate, you will find that you
will have to increase the welding speed or else
burn through, whereas when welding on heavy
plate, it is necessary to go more slowly in order to
get good penetration.
3. When welding sheet metal 16 gauge (1.5 mm) and
lighter, heat buildup may cause part warpage and
burn through. One way to eliminate these problems
is to use the back-stepping method illustrated in
Figure 15.
Practice
The best way of getting practice in the four skills that
enable you to maintain:
1. Correct welding position.
2. Correct way to strike an arc.
3. Correct Contact Tip to Work Distance.
4. Correct welding speed is to perform the following
exercise. Refer to Figure 16. Use PROCESS
GUIDELINES in the Instruction Manual and
Application Guide on the inside of wire feed section
door for selection of welding wire, shielding gas,
wire feed speed, voltage, and for range of metal
thicknesses that can be welded.
1. Position face shield to protect face and eyes.
2. Learn to strike an arc by positioning the gun over
the joint and touching the wire to the work.
3. Press gun trigger, hold gun so contact tip to work
distance Is about 3/8 to 1/2 inch (10 to 12 mm) and
the gun is at proper angle.
Contact Tip
Wire Electrode
CTWD
Molten puddle
Base metal
Push Technique
Weld metal ridge