roll cage joint preparation

[eric75]

I was just wondering, how do serious race shops fishmouth tubing for roll cages?

Most of the stuff I do is 1.25" OD x .049 wall, but what about NASCAR, NHRA, SCORE and the other guys with tube sizes up to 3" OD?

I've done it with a die grinder, done it with a hole saw, seen it done with an end mill, seen it done with a nibbler, seen pictures of joints cut with a CNC plasma cutter. But I have never seen anyone fishmouthing the roll hoop for a monster truck. Is it done with jigs and big cutters, or is it done freehand with a grinder?

Any insight you might have would certainly start an interesting discussion thread.
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[ASKANDY]

The 3 ways I do it here is a 90deg notching die for the ironworker and tube notchers like the ones shown here

http://www.mittlerbros.com

Andy

[tomasharvey]

Notched

I use the 'Ol joint jigger tube notcher with a hole saw. I know a few fabricators that still do it free hand with a 4 1/2" grinder and a die grinder. I personally have better things to do than sculpt fish mouths with a grinder!

I spent $250 on the notcher plus the saws. If your tigging the tube the notcher will make your life much easier and the cage/chassis with look awesome. As you know, fit up is No.1 and the notchers make it much easier!

Tom
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[tomasharvey]

Tube

Where are they using 3" tube? I am into drag racing and my car is 2x3 rectangle and 1 3/4" round. I are taking exhaust or fram? Just curious.

Tom

[Gaslight]

I use a 2hp belt sander, with a detail attachment, it burns out a radius in seconds. But it only works where you can bring the part to the tool. I'm not one of the glorious pros described, however.

Here is the link, metal just falls away in front of these machines. They will tailor the radius to your grind requirements.

http://www.beaumontmetalworks.com/kmg-swa.html

[eric75]

When I said 3" I may have been exaggerating a little. A roll cage made from that would not be very practical. The only time I've seen tubing that size is on the decorative "roll bars" that bolt into a truck bed.

That belt sander looks pretty good to me. When I get a workshop of my own and stop using the school's, I will have to get a sander like that.

After trying the joint jigger, I have settled on grinding by hand. Don't know if its the cheap hole saws, the worn out bushings on the tool, or the thin wall 4130, but the results required a lot of time spent grinding anyway. There were lots of burrs and the notch was never centered. The saw did so much walking that the notch would have ft better on a tube .250" larger diameter. Fit was much better by hand. Then again, I was using .049 wall tubing, so the tolerance for gap is less.

For exhaust or any type of pipe welding, I understand that both parts need to be cut so that flow can occur. I've never done it before, but the first tool I'd try for that is a good band saw.
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