ROLL CAGE DEFORMATION

[vetteracer]

Have started to build the roll cage for the corvette. I used a former I made years ago, and took it to the local exhaust shop, to bend up the "real" one in 44.45mm x .120 wall. One of the bends has deformed the tube to 39.5mm. With CAMS cages I have built before, I have worked on 10% max deformation, ie 44.5 - 4.45 = 40.05. What do scruts and experienced salties regard as the sensible limit. Sorry if this sounds anal, but Rob's 260mph prang post sent a very solid shudder down my skinny spine.
Thanks in advance, Denis

[Rob]

G'day Denis,

I can't answer your question but am curious as to what angle and radius you bent to that caused the tube to deform (for my own info).

In one of my conversations with Bond Rollbars they advised me to not go under 3.5 times the tube diameter for the bend radius or it may well deform. That would equate to 6 1/8" though I have seen commercial dies for 5.5" bends in 1 3/4" tubing suggesting the smaller bend radius is workable.

Cheers,
Rob

[vetteracer]

Hi Rob- it's p---g down right now so will check the angle tomorrow am. It would be 85ish- BUT I did a trial 300mm length, packed with sand blast medium, with ends welded shut, and the same angle bend deformed less than 10% Have cut, packed and welded the main hoop #2, so hopefully will be able to report back tomorrow night- Denis

[vetteracer]

Hi Rob-"sandpacking" worked well. Main hoop is done, and bends have less than 5% distortion. And , after putting my brain in gear, have answered the question in my first post. Have realised that the the reason I reached for the verniers after the first test bend, is that it didn't "look right" I also dug out a CAMS manual which says "...the centreline bend radius must be at least three times the tube diameter...where the tubing is distorted during bending, the ratio of minor to major diameter must be 0.9 or greater..." My tightest bend has a radius of about 6 inches, which obviously is close to the limit. My conclusion? What Mr CAMS said, but try to keep distortion to about 5%- thanks for your interest.

[Rob]

G'day Denis,

Thanks for the extra info, it's all worth taking on board, particularly with my own cage build to commence soon.

Cheers,
Rob