Every welder should know how to read and understand weld symbols on blueprints. Not only does this ensure that a project is assembled and completed properly, but it allows for increased quality and the completion of projects in a shorter period of time.
Why do something twice when you can do it right the first time?
Depending on where and how you learned to weld, you might be unfamiliar with the meaning of some or all welding symbols. If you’ve ever looked at a blueprint and just felt absolutely lost, don’t worry. Welding blueprints can look scary and more intimidating or complex than they actually are.
This guide will help you have a better understanding of the fundamentals of welding blueprints.
Covering everything from what the symbols and letters mean to interpreting reference notes and more—pretty soon you’ll be able to read a welding blueprint like a seasoned pro!
How to Read Welding Symbols
When you look at a welding blueprint, you’ll see three different perspectives. The front, top, and ride-side of the piece you’re working on. This is to help you understand what needs to be completed with a near 3-dimensional view of the project.
You’ll also notice several different symbols and letters next to the sketch of the project. These are used to help the welder identify what type of work needs to be completed.
Basic Welding Symbols
First, let’s start with the basics of a welding symbol. Welding symbols follow a specific structure to communicate the direction and type of weld that must be completed.
On every welding symbol, you’ll see an arrowhead that directs you to the location of the weld. This arrow is called a leader line and is drawn at a 45-degree angle pointing upwards or downwards to the weld joint.
The one end of a leader line is connected to a horizontal line known as the reference line. At the center of the reference line, you’ll notice either parallel lines or a geometric shape. This information is used to indicate the type of weld that needs to be completed.
On some blueprints, you may notice a tail at the end of a reference line. The tail can have several forks (or smaller lines) diverging off from it in different directions. Much like the lines and shapes on the reference line, the tail is also used to convey important information that the welder needs to know about the project.
The placement of welding symbols next to the reference line is very important. Particularly if the symbol is drawn above or below the reference line. If the weld symbol is drawn below the reference line, the weld should be completed on the side of the joint the arrow is pointing at. If the weld symbol is drawn above the reference, the weld needs to be completed on the opposite side of the joint that the arrow is pointing at.
Sometimes, you may see a weld symbol drawn above and below the reference line. In cases like this, multiple welds need to be completed on both sides of the joint.
When it comes to the welding symbols, many different shapes can be used. If you’re just starting and haven’t memorized these geometric shapes yet, don’t be afraid to print out a chart you can keep on hand to reference as your work.
Many welders (even experienced ones) will keep a chart taped to their machines so it can be referenced as needed.
What the Letters on Welding Symbols Mean
You won’t find just shapes, numbers, and lines on a welding blueprint; you’ll also see different letters. As with shapes and lines, these letters are used to communicate important information. Welding symbol letters tell you different things, like the length of the bead of the weld or the root opening.
Here is a brief list of what these letters mean. Again, if you’re just learning to read welding blueprints, don’t be afraid to keep a copy of this cheat sheet near your welding machine.
A – Angle of the Countersink
C – Chipping finish
F – Finish symbol
G – Grinding finish
L – Length of the weld bead
M – Type of machining finish
N – The number of spot welds or projection welds required
P – Pitch of welds
R – Root opening or depth of the filling
S – Depth of preparation required
T – Specification process
Welding Symbols – Dimensions and Angles
Welding blueprints are loaded with helpful information needed to complete a project.
Angles and dimensions are used to communicate the proper length, width, depth, and opening of a weld. Reading a welding blueprint is actually quite simple if you can decipher the angles and dimensions next to welding symbols.
The width or diameter of a weld is noted on the left side of a weld symbol. It is written down as a fraction of an inch. ¼ for instance, means the width of a weld should be a quarter inch.
The length of the weld is also expressed in inches. This number is noted on the right side of the welding symbol. As an example, let’s say the blueprint is instructing you to complete a quarter-inch wide weld that is 4 inches long. The blueprint would have ¼, then the type of weld symbol next to it, and then a 4 to the right of the symbol.
If you need to complete welds on both sides of a joint, a symbol will appear on both sides of the reference line. Where those symbols are located on the line is also important to note.
If the symbols are in line and mirror each other on both sides of the reference line, the welds should as well. However, if the symbols do not mirror each other, this tells you that the welds should be offset.
Pay attention to the numbers written next to the symbols. Just because welds need to be made on both sides of the joint, the width and length of those welds may differ. Remember, numbers and symbols drawn below the reference line indicate what needs to be done on the side of the joint the arrow is pointed at. Numbers and symbols written above the reference line indicate the work to be done on the opposite side of the joint.
One final thing to note here is a flag you might see on some blueprints. If you notice a flag at the intersection of the reference line and leader line, do not complete this weld inside your shop. The flag is used to indicate that this weld needs to be completed in the field.
Common Types of Weld Symbols
Each type of weld has its own symbol, which is drawn near the center of the reference line. These symbols can appear on one or both sides of the reference depending on the project and what welds need to be completed.
Fillet welds are used to make lap joints, corner joints, and T joints. This symbol often appears as a right-angle or isosceles triangle. The perpendicular leg is always drawn on the left side of the symbol regardless of the position of the symbol above or below the reference line.
A groove weld is often used to make edge-to-edge joints. It can also be used for corner joints, T joints, and joints between curved and flat pieces. There are many different kinds of groove welds that each have their own unique symbol to represent them. The different types of groove welds include:
- Square Groove Welds
This type of weld has either a tight fit or slight separation between the edges. Square groove welds are drawn as two vertical lines next to each other. If there is a fraction in between the lines, it indicates how separated the edges should be.
- V-Groove Welds
With this weld, the edge of each piece is chamfered to create the groove. The weld symbol is drawn as a v with the angle of the edge indicated in the center of the v.
- Bevel Groove Welds
A bevel groove weld is used when the edge of one piece is chamfered, and the other is left square. This symbol looks similar to a right angle triangle with a missing side. The arrow points toward the side that is chamfered, and a number in degrees indicates the bevel of the edge.
- U-Groove Welds
A u-groove weld can be used when the edges of both pieces have a concave shave. This weld symbol is drawn as a semicircle with the open end facing away from the joint.
- J-Groove Welds
A J-groove weld can be used when the edge of one piece has a concave shape while the other piece is left with a square edge. This symbol is drawn as a vertical line on the left with a quarter circle line intersecting it on the right side.
- Flare-V Groove Welds
A Flare-v groove weld is used to join two rounded or curved pieces together. The symbol is drawn as two-quarter circles next to each other. The intended depth of the weld itself will be written to the left side of the symbol with the weld depth next to it in parenthesis.
- Flare Bevel Groove Weld
A flare bevel groove weld is commonly used to join flat and round pieces of metal together. This type of welding joint is drawn as a vertical line perpendicular to the reference line. On the right side of the vertical line is a quarter circle with the open end facing away from the vertical line.
- Plug and Slot Welds
Plug and slot welds can be used to join overlapping pieces. This type of weld is drawn as a rectangle that is wider than it is tall on either side of the reference line.
Welding Blueprint References and Notes
When you’re reading a welding blueprint, there will be a lot of important information to read and understand. With so much information on the blueprint, certain details may only be listed in one place if they are to be followed throughout the entire welding portion of the project.
There are generally two ways this information is noted so that it’s easier to read the blueprint.
Symbols Without References
If a certain specification or process needs to be followed, this information is placed next to the tail of the reference line.
In some circumstances, those specifications may be the same for multiple welds. When that happens, you may start to see just symbols and no references next to the tail.
Blueprints will be written like this and have symbols without any specification when either:
- A note similar to this is written on the blueprint: “Unless otherwise noted, all welds should be completed following the instructions listed with specification #…”
- The welding procedure that should be followed is conveyed elsewhere on other process sheets or through in-shop instruction from a supervisor.
Sometimes there may be general notes written on the blueprint. These notes are used to convey information that relates to the majority of the welds and doesn’t need to be repeated over and over on every reference line. Most general notes will look something like this:
- “Unless stated otherwise, ensure all fillet welds are ¼ in. (0.635 cm) wide.”
- “Unless stated otherwise, the root opening for any groove weld should be 3/16 in. (0.481 cm) in size.”
Understanding Welding Symbols and Blueprints
As you can see, a lot of information can be conveyed in a tiny welding symbol on a blueprint. But, once you start to understand what the different shapes and numbers mean, they aren’t as intimidating to follow.
Learning how to properly read welding symbols and blueprints is a foundational skill that every welder needs to learn. If you want to learn more about reading blueprints and further develop your welding knowledge and skills, you should consider joining Welder101.
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