Fillet welding can have so many confusing terms, leaving most amateurs confused. One especially confusing terminology in fillet welding is throat thickness and how it pertains to fillet welding. If you’re just getting started with fillet welding, you may want to ask: what is actual throat thickness?
The actual throat thickness is a measure of the distance between the foot and the face of the weld. It is usually the main way to decide if a fillet weld is concave, convex, or miter.
In this article, you’ll learn what throat thickness means, and how it relates to fillet welding. You’ll also learn how to determine the actual throat thickness for a fillet weld to get the desired results with your works.
What’s a Fillet Weld?
Throat thickness is a terminology common to fillet welders. To understand what throat thickness means, you’ll need a basic understanding of fillet welding, at the very least.
A fillet weld refers to any welding job that lets you join two pieces of metal at a right angle or perpendicular to themselves. After completing an ideal fillet weld, the result will be in the shape of a T, and in some cases, L.
The fillet weld is an excellent alternative to a butt weld, but instead of joining things end to end alone, fillet welds mostly join metals to be one T or L-shaped.
While it’s easier for amateurs to describe fillet welds as either T-shaped or L-shaped, that will be regarded as unprofessional in the standard welding world. There are better ways to describe different weld shapes, most of which have been adopted as the industry standard.
There is the miter fillet weld, the concave fillet weld, and the convex fillet weld. These are the industry standard names used to describe the different types of fillet welds and most professionals stick to using these.
A miter fillet weld is usually in the shape of a right-angled triangle due to the cross-sectional nature of the weld. Concave fillet welds are similar to miter fillets, but instead of being completely flat, they bend inwards to give a concave shape.
Convex fillets are also similar to their concave counterparts, but they bend outwards to earn the convex name. These fillets have different applications, and one isn’t in any direct competition with another.
While a layman can differentiate between these types of fillets using their bend direction, professionals measure it using the throat thickness. You can easily tell the difference between convex and concave fillet welds by measuring the throat thickness with respect to a miter fillet weld.
In the next section, you’ll learn what throat thickness is actually, and how you can tell the differences between these fillet welds using throat thickness.
What Is Actual Throat Thickness?
At this point, you should already know that throat thickness is an important value that determines the quality of a weld. However, there is still much more to know about what throat thickness actually means.
Throat thickness, also known as throat size, is a measure of the approximate distance from the face of a weld to the root of the weld. While that sounds simple, it’s pretty impossible to comprehend if you don’t know what the face or the root of a fillet weld means.
In a fillet weld, the face of the weld refers to the diagonal between the two toes of a fillet weld, while the root is the base metal of the fillet weld. The throat thickness of a weld simply refers to the distance between these two points.
To have a passably solid job, you must ensure that the throat thickness is the same value as the thickness of the metal you’re welding, at the very least. The degree of the thickness is what differentiates a concave from a convex fillet weld.
The actual throat thickness, also known as the effective throat thickness should be at least 3mm for any weld. The value of the maximum throat thickness is usually expressed as 0.7t, where the t stands for the thickness of the plate of your weld.
It’s usually difficult to measure the throat thickness of your weld precisely. However, the next section will help you determine this with some precision, helping you create fillet welds without craters and other faults.
How to Calculate Actual Throat Thickness
Having a good idea of what throat thickness means is pretty useless if you can’t calculate the idea value that it should be for your particular weld. While the welding field isn’t known for complex calculations, finding the throat thickness of a weld is notoriously difficult.
Part of this difficulty is associated with the fact that there are many throat thickness values. In this case, we’re focusing on actual throat thickness, which is somewhat different from theoretical throat thickness.
To get the value of the actual throat thickness, you may have to find the leg length. Then, you can calculate the value of your weld’s throat thickness using the actual leg length value.
With equal leg lengths, the value of the throat thickness will be akin to the hypotenuse when both of these lengths form a right angle. When calculating, you can represent the leg length with Z, while the throat thickness is usually represented with an “a”.
Most fillet welds have equal leg lengths, which negates the need to have two different values for them. If your leg lengths are unequal, you’ll have very different values from the quoted samples.
The relationship between the throat thickness and the leg length is that the leg length is the product of the square root of two and the throat size. Since you already know the leg length, you can calculate the value of the throat size by reversing this equation.
Finally, the formula for calculating the throat thickness will be the leg length divided by the square root of two. If you want a quick value without much hassle, you can use 1.41 as the value of the square root of two.
