How to weld a mild steel roll cage

[Laiky]

how do they check the wall thickness?

[dabar39]

how do they check the wall thickness?

Drill a small hole and use a depth gauge, at least all the tracks that have checked my cages have done it this way. Dave

[diverbill45]

Pro70, ......... There's quite a few different organizations that run different events and most of them have their own rules, so it does make it kinda hard to keep up with all of them. I'm in the planning stages of building a car for the Reno to Vegas run (haven't made up my mind to do it yet, just thinking about it) and they have a different rulebook than the Baja 1000 bunch. I might add that each year some of these rules change, so you have to keep up on everything, each year. I know it's a PITA, but it's for our own safety, and I might add, with this country being the sue capital of the world, each racing organization is just trying to keep these suits to a minimum, when and if this happens to arise.

The weekend circle track here, in the town where I live, even has their own set of rules, which leaves a lot to be desired. I've seen quite a few guys get bumped at the inspection, because of this one little item. I heard a few of them say "The rule book says that the min. wall is .xxx and that's what I put in." Some of them just don't understand what happens when you start bending tubing.

I just wanted to pass this info along, because after going to all the trouble and expense of building a roll cage, it would be a shame to have to cut it all apart because of not knowing exactly what is required.

[Vicegrip]

The groups I design and build to conform to all rule on the wall thickness of the tubing that is used not so much the thickness after forming. The wall thickness inspections holes for the groups I build to (Road racing, no drag or circle) are drilled in straight sections of the main hoop and other major tubes. Most groups, SCCA is a good example, have rules about how tight a bend can be in order to maintain the integrity of the tubing. I would think that the tube wall thickness rules take the elongation and compression of the tubing in bends into consideration.

Geometric design plays a great role in the performance of a cage. You can make a cage that uses lots of thicker than called for tubing it will still not be a good cage if poorly designed. I see plenty of cages that have extra tubing that does little and areas that should have has a little more but do not. Things like tube shapes that should make an “X” or “Y” or "V" only intersecting near each other rather than directly opposing each other in self reinforcing nodes. Some builders use square shapes when triangles could have been used. I love triangles, they are the key to geometric rigidity and strength. You can make something strong and stiff by making it massive via Material strength or you can do the same by making it smart via Geometric strength. An “A” is stronger than an “E” so to speak.

[Craig in Denver]

Drill a small hole and use a depth gauge, at least all the tracks that have checked my cages have done it this way. Dave

How do you drill a hole in a tube and measure wall thickness? I'm picturing a depth mic (which would cover the hole), and it would read to the far wall; not just the .134". AND, how big a hole do they drill?

Thanks, Craig

[pro70z28]

The gauge has a hook on the end. You stick the hook in the h o l e and then pull back until the "barb" of the hook contacts the inside of the tube.
NHRA / IHRA use sonic meters. Little grease on the sensor to get good contact and hold it to the tube. Care has to be taken to calibrate the meter correctly to get an accurate reading. They always check the straight sections of the tube also. And, bends can only be so many degrees in certain places.

[Craig in Denver]

A hook!

pro70; Thanks.

[Vicegrip]

The gauge has a hook on the end. You stick the hook in the h o l e and then pull back until the "barb" of the hook contacts the inside of the tube.
NHRA / IHRA use sonic meters. Little grease on the sensor to get good contact and hold it to the tube. Care has to be taken to calibrate the meter correctly to get an accurate reading. They always check the straight sections of the tube also. And, bends can only be so many degrees in certain places.

The hook method might result in inaccurate measurements as it can measure drill hole flash. I scrut for a car club racing league and the standard method is to use a drill and a digital verner caliper. We measure the tube diameter and note the size in the log book. Then I drill a hole, make sure there is no flash at the hole and measure through the hole from outside surface to inside of the tubes far side. Now I zero the digital caliper and directly remake the diameter measurement. This produces the tube wall thickness in the caliper and no math needed. Sounds complicated but it takes about 1 min and is dead on when done right.

[Craig in Denver]

Vicegrip:
I wondered about the inside burr. And, I understood your explanation; that scares me.
It was the 'no math needed' that caught my eye and made me figure it out.

Thanks, Craig

[chrisgay@sbcglo]

The hook method might result in inaccurate measurements as it can measure drill hole flash. I scrut for a car club racing league and the standard method is to use a drill and a digital verner caliper. We measure the tube diameter and note the size in the log book. Then I drill a hole, make sure there is no flash at the hole and measure through the hole from outside surface to inside of the tubes far side. Now I zero the digital caliper and directly remake the diameter measurement. This produces the tube wall thickness in the caliper and no math needed. Sounds complicated but it takes about 1 min and is dead on when done right.

Why a digital caliper?