Tubing wall thickness tolerance clarification

[UCIrvine FSAE]

The rules state that the main roll hoop must be at least 0.095 inches thick for a 1 inch OD tube. Our team bought 13 gauge tubing, which according to our research, should be 0.095 inches thick, but when we measured the wall thickness it was actually 0.090. We contacted the manufacturer, who said that their tolerancing meets ASME standards. We are wondering if, in light of the fact that our tubing meets ASME standards for 13 gauge, 0.095 thick tubing, would it be acceptable to use for our main roll hoop even though it is undersize, or do we have to find a source of more accurate tubing and buy more?

[UCIrvine FSAE]

The rules state that the main roll hoop must be at least 0.095 inches thick for a 1 inch OD tube. Our team bought 13 gauge tubing, which according to our research, should be 0.095 inches thick, but when we measured the wall thickness it was actually 0.090. We contacted the manufacturer, who said that their tolerancing meets ASME standards. We are wondering if, in light of the fact that our tubing meets ASME standards for 13 gauge, 0.095 thick tubing, would it be acceptable to use for our main roll hoop even though it is undersize, or do we have to find a source of more accurate tubing and buy more?

[Hector]

Once again, email the rules committee.

No answer you get here will be official, and if we say "yes" and you get to comp and find out the answer is "no", you're screwed.

[ibanezplayer]

Roll-hoop wall thicknesses are checked at comp. You'd have a tough time getting by with that, especially for something so critical.

[D Collins Jr]

You're a clever guy, you can probably figure this out. I'll give you a hint though, paint has mass, and volume. That probably means that it adds some thickness too.

[ibanezplayer]

All hoops are now tested with ultrasonic testers, the scrutineers could tell you exactly how thick your wall is, as well as your coatings inside and out.

@ D Colllins Jr: as a FSAE/FS competitor you represent your entire school, the faculty, and your sponsors. I can't believe a member of the Sooner team would advise someone to do something so devious. What you say could impact potential sponsorships, or future employment.

[D Collins Jr]

@ibanez: You're quite right. It was irresponsible of me to make such a foolish post under a public profile. I should have done what many before me have done and created a secondary user name to post under for this purpose. This is far from the worst thing that has been posted on these forums wrt professionalism, respectfulness, legality, etc.

Now that that is out of the way, what ibanez says is true, the tech inspectors do use ultra sonic gauges to check tubing thicknesses. This means that all your tubes must be within spec. However, i can say without a shadow of a doubt, that the .095" wt tubing that is on our roll hoops measures at over .1" thick at competition every year.

Obviously, the best solution is to call the fine folks at Wicks Aircraft (or another aircraft tubing supplier) and get your hands on some genuine, 4130, 1" x .095" tube. But at this point, it becomes a decision for someone else to make, since it isn't my team.

[fixitmattman]

The minium tubing spec is 1x.095, but that's a NOMINAL dimension tube spec. As you're finding between rolling tolerances, concentricity, etc. you don't always get a perfect wall thickness every time. I've had several cars with FSAE and BAJA which were a few thousandths under (within published spec) and passed tech just fine at comp. This includes the use of the ultra sonic testers as well. But as usualy, if there's any doubt it's best to check with the rules comittee to get an official clarification.

As for the paint idea, these guys aren't idiots. They know all the same tricks we do and probably half the rules in the book are from things they did in the past. They know what to look for.