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Are fat blobby welds inferior, other than aesthetically?

Here's three examples, one's a BSO, one's a decent/good Trek and one's an expensive Felt downhill full-suspension bike.

BSO welds welds on a better-quality bike welds on Felt downhill bike

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    There are a bunch of layers to this question, and it would help to know if you were asking about MIG (blobby/ugly looking, controversial and not commonly seen on bikes due to some technical parts of its nature) versus TIG (neater, how most welded al and steel frames are made), messy versus neat TIG joints, the different appearance between al and steel TIG joints, etc. – Nathan Knutson Apr 3 '17 at 20:54
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    Generally speaking, "blobby" welds are considered inferior. In addition to looking ugly and "sloppy", a weld that lacks uniformity will tend to concentrate stresses inappropriately and be weaker and more failure-prone than a smoother weld. – Daniel R Hicks Apr 4 '17 at 0:35
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    Conversely, a smooth and pretty weld is considered the mark of a craftsman. Ideally an invisible or flush weld means the lowest airflow disruption too. – Criggie Apr 4 '17 at 1:34
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    Welding what? Mass-produced aluminium welds seem to be blobbier than equivalently priced mass-produced steel welds, for example. – David Richerby Apr 4 '17 at 8:43
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    Welds of the pictured quality, while not ideal, are generally OK. If you can see a "joint" -- the appearance that the welding was stopped and restarted -- between two adjacent blobs then that's not good. – Daniel R Hicks Apr 4 '17 at 12:09
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Assuming good penetration, a “thick” weld also functions as a fillet reinforcing the joinder. The “swirly” look is OK as long as the welding puddle is continuous. In many instances a “stitch weld” is more fatigue resistant than a continuous bead by limiting stress risers in the weld.

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No, from the perspective of a bike owner/user, there's nothing inherently wrong with fat blobby welds. While the quality of individual welds can vary, they're not automatically bad simply because they're fat and blobby, and can be perfectly fine.

Some other considerations (pointed out by people with specific knowledge of welding and frames -- i.e., not me -- in comments and in other answers):

  1. A good weld is continuous. A visible line where the weld stops and starts again can indicate an inferior weld.
  2. There is such thing as too much blobbiness, which can lead to unwanted concentration of stress in the weld.
  3. Conversely, a proper zig-zag or stitch weld can prevent stress concentrations (per @TomO's answer).
  4. A thick weld can reinforce the joint (per @TomO's answer).

 

See also: Aluminum frame quality - how much variation can there be and how to tell?

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