ChampCar Tech Desk

The tech desk is used to ask technical questions and is not to be used as a post race tech line or to phish for how others built their cars.
Please reference the BCCR as most questions submitted to the TechDesk can be answered by reading the BCCR.
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2020-02-27 - Roll Cage Welds

Are welds that have been sanded to blend in with some of the cage profile are considered acceptable? Something like in the attached images.

Example Image 1 Example image 2

1. Grinding cannot result in a reduction in the diameter of the tube of more than .050". That would be 25% of the wall thickness (.095 * 2 = .200, .050 would be 1/4). This means the tube better be 1.70" or greater for a 1.75" cage.
2. Grinding marks need to be dressed down with higher grit paper to remove visible scratches\gouges. It needs to look like the rest of the tube in smoothness, otherwise, you have left stress risers that can cause it to fail.

You need to maintain the added cross-section of a weld. That means I expect the weld joint to have some bead height greater than the rest of the tube. 1/16 or maybe 1/8" or more over the base 1.75" diameter. Do not grind the welds flush with the tube to look good. If you booger up a weld you can grind it down and build it back up with a hotter weld (turn the machine up one heat setting, which you most likely needed to do the first time anyway), but it should look like a wider version of a good weld with properly added cross-section that is "burned in" at the edge of the weld bead, not a convex sharp edge that looks like you put a twinkie on a table.

The welds shown in the example images don't look like they had good penetration.
If one weld fails the whole cage fails. Those ground down welds most likely need to redone unless they meet the thoughts above.
If you want to be sure contact tech and send pictures of all the welds.

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