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Old March 30th, 2017, 11:43 AM   #50
I-ROBOT
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Join Date: January 7th, 2007
Location: Hudson, MA
Posts: 391
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To calm everyone's fears:

NO they are not cracks, just minor surface irregularities. Typically they are the result of minute oxidation reactions on the hot surface since it is virtually impossible to shield the weld zone completely just using a conventional TIG torch. I built a trailing shield that attached to the torch for welding the downtube gussets which helped with shielding that large area but you still get some straw and a even a little blue coloring on the welds. That is why all of the TI frames were glass-bead blasted and have that satiny finish. The only way to avoid any oxidation is to weld the part inside of what is known as a "dry box". The air in the dry box is sucked out by a vacuum pump down to negligible levels (which also removes all moisture - hence the term dry box) and then the box is back-filled with pure argon so all traces of reactive gases and moisture are gone and then you leave the part in the box until it is cooled below the reactive temperature (I think for TI that is about 400F)

One of the coolest things about TI welding is that when you complete the weld, the surface is a virtual mirror and you can see yourself in the reflection. As much as I would have liked to leave the mirror-finish welds, we would always have a little discoloration which would spoil the look, so they were bead blasted. You could polish the welds if you chose to and those surface irregularities would disappear.

There was one guy who worked at Merlin for a while who polished his entire frame and it was absolutely blinding out in the sun. Think it took him about a month to do it.

If it makes you feel better, you could perform a liquid penetrant examination of the welds and you would find that the irregularities do not extend more that a few millionths deep and do not hold enough penetrant to reveal any rejectable indications.

Hope this helps
Scott
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