Arrow Leader Line Reference Line Tail
Arrow Leader Line Reference Line Tail
Arrow Leader Line Reference Line Tail
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Dangling from the middle of the reference line, you'll see a geometric
shape or two parallel lines identifying what type of weld should be
performed on the metal. This is called the weld symbol (not to be
confused with the overall welding symbol ). The three weld symbols you
see in the drawings above represent a square, fillet and V-groove weld,
respectively.
The weld symbol may also be placed above the reference line, rather
than below it. This placement is important. When the weld symbol hangs
below the reference line, it indicates that the weld must be performed on
the "arrow side" of the joint. For example, In the next drawing a fillet
weld is specified on the arrow side. You can see the actual weld in the
second depiction.
Now, if the weld symbol appears on top of the reference line, then the
weld should be made on the opposite side of the joint where the arrow
points. Here's how that will look:
If the weld symbol appears on both sides of the reference line, as shown
below, it specifies that a weld must be performed on both sides of the
joint.
Numerous weld symbols have been devised to represent all the different
weld types used in the trade, as well as any joints that must be cut or
beveled during fit-up. Here are the most common ones to learn:
If you're not familiar with either welds or joints, be sure to check out
those topics in the green menu box located on the top right side of this
page. Even if you are familiar, it still takes time to memorize all these
symbols and what type of welds they represent. Therefore, it's a good
idea to print out or photocopy a chart that contains both the symbols
and drawings of the completed welds. Click here to download a sample
chart or look below right of this column.
In most cases, the weld width (or diameter) is located to the left of the
weld symbol (expressed here in inches), while its length is written to the
right . (As explained in Anatomy of a Weld, the weld's width is the
distance from one leg of the weld to the other.) Often, no length is
indicated, which means the weld should be laid down from the
beginning to the end of the joint, or where there's an abrupt change in
the joint on the base metal.
Dimensions written below the reference line, of course, apply to the joint
on the arrow side, while dimensions written above apply to the joint on
the other side. In the image above, welds are indicated for both sides of
the joint.
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Notice that the weld symbols on either side of the reference line above
are offset, rather than mirroring each other. This means the welds
should be located at staggered spots on either side of the joint, as
shown in the drawing on the right.
A weld symbol may also specify an angle, root opening or root face
dimension. This is common when the base metal to be welded on is
thicker than 1/4 inch. The following example is a symbol and drawing
calling for a V-groove joint:
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Here, the groove weld has dimensions written inside the symbol. The
first is 1/8 , which pertains to a root opening of 1/8 inch. The larger
number below it signifies 45 degrees, which represents the included
angle between the plates. "Included" means the sum of the angles
beveled on each side. So in this example the bevel made on each plate
is 22 1/2, which equals 45 degrees.
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Here are a few other types of instructions you might see on a drawing:
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A curve located above the weld symbol's face specifies that the finished
weld should be either flat, convex or concave. (If you see a straight line,
then it's a flat weld - i.e. flush face.) As shown on the top right, a V-
groove weld symbol with a box above it indicates a backing strip or bar
is required for this joint. The strip or bar must be welded onto the back
side of the joint before the groove weld is performed.
To keep the instructions clear, several reference lines may extend from
the leader line at a parallel trajectory. Each line represents a separate
operation and is performed in order, beginning with the line closest to
the arrow.
As you just saw in the case of the backing strip, the forked tail of the
welding symbol is used to convey details that aren't part of the normal
parameters declared on the reference line. For instance, the engineer or
designer might want the welder to use stick welding (i.e. SMAW), or
another welding process. Or there may be other information to convey:
Of course, when no special instructions are needed, the tail is omitted
from the welding symbol, leaving just the reference line, arrow and
leader line.
Once you master the basics, you'll be ready to absorb the many other
particulars conveyed on shop drawings and blueprints. Among the most
common:
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