I'm building a cage for my 1977 Datsun 280z. I plan on building the main parts of the cage from 1.625 X 0.083" 4130 tubing. Do I need to go to a slightly thicker walled tubing so around the bends, the thinnest part of the tubing is still 0.083" wall thickness?

I'm thinking I might have to source sometime around 0.095" wall thickness if that is the case.

Regards,
Justin

 

You base the material specs off of what it is when you buy it. So yes, you just use 1.625" x .083". As long as you have a good bender the reduction in wall thickness is very minimal.

 

Do I have to worry about mill variances on 4130? I've read that mill variance can be between 2-4 thousandths on DOM tubing.

Regards,
Justin

 

You can determine wall thinning by using this formula. This formula only applies to non pressure assisted rotary draw benders though. (jd2, jd3, ercolina, rmd, etc)

WT – (( OSR – CLR ) / OSR x WT ) = RWT

where “WT” is the starting wall thickness, “OSR” is the outside radius, “CLR” is the centerline radius, and “RWT” is the thickness of the wall after being reduced by bending.

For example, in a 1.625” TOD x .083” WT x 6” CLR tube bend, the calculation for the target post-bend wall thickness is .083 – (( 6.81 – 6 ) / 6.81 x .083) = .073 for a 6" CLR. So the outside wall of the bend will be .073" in with an ideal machine setup.

Same #s, 4" CLR, outside wall will be reduced to 0.069".

Mill variance with DOM tube is usually tighter then +/- .003.

 

I just want to make sure that I wont be shooting myself in the foot with getting the cage certified. I've just reread some of the rules and it seems they sonic test the straight sections of the tubing. So as long as the tubing I order is over .083" I'll be golden.

Regards,
Justin

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">I just want to make sure that I wont be shooting myself in the foot with getting the cage certified. I've just reread some of the rules and it seems they sonic test the straight sections of the tubing. So as long as the tubing I order is over .083" I'll be golden.

Regards,
Justin</TD></TR></TABLE>

The NHRA is a joke at certifying cages. Most sanctioning bodies are for that matter... I've seen the SCCA pass cages that weren't welded all the way around on top of the main hoop and I've seen them pass cages that were made of .065" wall material when it should have .095" and the owner of the car died later in a car wreck. The NHRA passes some of the most backwoods half-assed welding ever.

Maybe they should hire competent techs. No, that's crazy talk.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by david@didrace.com &raquo;</TD></TR><TR><TD CLASS="quote">

The NHRA is a joke at certifying cages. Most sanctioning bodies are for that matter... I've seen the SCCA pass cages that weren't welded all the way around on top of the main hoop and I've seen them pass cages that were made of .065" wall material when it should have .095" and the owner of the car died later in a car wreck. The NHRA passes some of the most backwoods half-assed welding ever.

Maybe they should hire competent techs. No, that's crazy talk.</TD></TR></TABLE>

Let alone the beads of silicone sealant that we all know have been passed as weld beads... Just add paint!
OP, you should be fine.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by david@didrace.com &raquo;</TD></TR><TR><TD CLASS="quote">

The NHRA is a joke at certifying cages. Most sanctioning bodies are for that matter... I've seen the SCCA pass cages that weren't welded all the way around on top of the main hoop and I've seen them pass cages that were made of .065" wall material when it should have .095" and the owner of the car died later in a car wreck. The NHRA passes some of the most backwoods half-assed welding ever.

Maybe they should hire competent techs. No, that's crazy talk.</TD></TR></TABLE>

I agree. Iv seen so many cages where I am suprised as to how they passed. Iv seen bars missing, unwelded bars, inccorect OD bars, welding which i would call welding...

 

Our local NHRA guy is very picky for a tech guy.
He must have turned about 5 guys away last time I went.
He hits pretty hard on fitment. If the weld is wide, he assumes a bad gap, and won't tech it.
He seemed pretty fair.
Then you get the guys who want you to do things that aren't even in the rulebook...That's when you hand him a current copy, ask to see it in writing.

I've seen some ridiculous welds on the road cars I marshall for though, it's scary.

 

Does the 4130 tubing need to be seamless?

Regards,
Justin

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">Does the 4130 tubing need to be seamless?

Regards,
Justin</TD></TR></TABLE>

Yes, I haven't seen any rules for roll cages where the materials haven't been seamless (DOM).

 

Cool, I was just double checking. I purchased 100ft of 1-5/8" X 0.083" 4130 seamless tubing for $400 delivered. Is that a pretty good price? $4/ft?

Regards,
Justin

 

Yup, around here last time I ordered some it was $6.5/ft picked up.