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Thu Mar 06, 2014 10:06 am

I'm going to be designing a basic tube frame/rail chassis for a solidworks class that I'm in now, and I'm curious what the common diameter and wall thickness for these type of frames. I'd like to make the model actually using pipe instead of making it a solid model, because I'm going to need to provide weight.

Also, what kind of steel tube is commonly used? Is it just an A500 steel?

Thanks in advance
Jameson

Thu Mar 06, 2014 10:17 am

A lot of people subscribe to using something like .095 th wall DOM tubing in the 1.5 inch category for main chassis components, and some bracing can be in smaller diameters (1 inch) when used in straight linear loading.... For actual roll cage assemblies (hoops and braces) .120 wall DOM is better!

Be careful in describing product, because tubing is not pipe and pipe is not tubing.....

Tubing is measured in OD and pipe is measured in ID....

Your weight will be in pounds per foot of material so you just need to total of feet of material in build.... Weights should be part of tubing specifications....

Dale

Thu Mar 06, 2014 1:53 pm

Most of ours is T45 in 1-3/4" diameter, 0.08" or 0.096" wall thickness. Odd bit of 1.5" dia 0.08WT here and there

Thu Mar 06, 2014 3:07 pm

Here we are not building race cars, just play cars and use .120 and .095 wall 1 1/2" ERW and it has worked great. Also some .120 and .095 by 1" for some braces. Our metal supply house sell them in 20' pieces. To step up to DOM is quite a bit more money here.

Ed

Thu Mar 06, 2014 11:00 pm

Dale M. wrote: A lot of people subscribe to using something like .095 th wall DOM tubing in the 1.5 inch category for main chassis components, and some bracing can be in smaller diameters (1 inch) when used in straight linear loading.... For actual roll cage assemblies (hoops and braces) .120 wall DOM is better!

Be careful in describing product, because tubing is not pipe and pipe is not tubing.....

Tubing is measured in OD and pipe is measured in ID....

Your weight will be in pounds per foot of material so you just need to total of feet of material in build.... Weights should be part of tubing specifications....

Dale

Once I make the model and assign the material, Solidworks will calculate weight.

Thanks for the tips everyone. This will never get past a basic solidworks model. But hopefully once I hit college in the fall and I get more fluent in modelling programs, I'll start making full models with suspension components and the works.

-Jameson

Fri Mar 07, 2014 12:59 am

Island Bumpkin wrote: I'm going to be designing a basic tube frame/rail chassis for a solidworks class that I'm in now, and I'm curious what the common diameter and wall thickness for these type of frames. I'd like to make the model actually using pipe instead of making it a solid model, because I'm going to need to provide weight.

Also, what kind of steel tube is commonly used? Is it just an A500 steel?

Thanks in advance
Jameson

I've never built a VW baja, but I have built a handful of SAE bajas in school. 4130 is the most popular tubing used in our competition, but we also use some 1020 DOM. Most mild steel tubing I've found are ASTM A-513 Type1/2/5, with 1 and 2 being ERW and 5 being DOM. Also there are some videos on youtube that are useful for making the weldment profiles you need to apply to your 3D sketch. Also I'll make the point that if you're not welding on heavy duty tabs or such, a larger diameter thinner wall tubing is usually stronger and heavier. We use only only 0.065 and 0.035 tubing in our cars in 1.25", 1", and 0.75", and it's actually lighter and stiffer/stronger than our old 0.120/0.095/0.065 frames made out of primarily 1". It's something to think about that I don't think gets must consideration in the VW world because I think people are afraid of dents from the thin tubing. 0.065 is pretty hard to dent without trying, but all bets are off for the 0.035 we use!

Mon Mar 10, 2014 6:13 pm

Also occurred to me as I'm starting the design, I have zero reference for dimensions. Anybody have just some basic dimension? If I can get a pan size and shape worked out, I can figure out the rest.

Tue Mar 11, 2014 7:56 am

Here is dimensions of standard beetle pan.... Length is probably ok for light "sand rail".... But it also gives you some usable dimension for rear suspension and so on.... Keep in mind the "front axle" center line dimension is not exactly correct, its actually center line of front beams and "axle center line" is actually behind front beam by about 10-12 inches because of way spindles are mounted on trailing arms....

Also the 14.5 dimension is typical "cut lines" for shortened pan for FG tub buggy...

Dale

Tue Mar 11, 2014 8:42 am

Thanks for that.

I started on something with a 112 inch wheelbase last night. Began working on the front end, which will be set up for A-arms. Got a decent start, but the first vertical offset I made was too tall. Going to have to go back and make it a little shorter.

-Jameson

Tue Mar 11, 2014 11:51 am

I have an engineer friend who built a mockup cage for his 510 using PVC tubing. The stuff bends OK with a good heat gun and patience. Folks who saw it and didn't understand his plan were pretty upset. The steel cage is wonderfully done and fits much better than average.
The SCCA rules more or less say under 2000#, .095 wall and over 2000#, .120 wall. It's more complicated, but this is a good rule for this question I think. ERW has fallen out of favor because it tends to split along the weld and make very bad bayonet like things. DOM doesn't. CrMo tubing really needs a full heat treatment in an oven after welding and that is beyond most of us, so it is not the place to begin either.
Dennis

Wed Mar 12, 2014 10:15 am

Weight per foot: OD -wall x wall x 10.68

Fri Mar 14, 2014 10:39 pm

DHale_510 wrote: I have an engineer friend who built a mockup cage for his 510 using PVC tubing. The stuff bends OK with a good heat gun and patience. Folks who saw it and didn't understand his plan were pretty upset. The steel cage is wonderfully done and fits much better than average.
The SCCA rules more or less say under 2000#, .095 wall and over 2000#, .120 wall. It's more complicated, but this is a good rule for this question I think. ERW has fallen out of favor because it tends to split along the weld and make very bad bayonet like things. DOM doesn't. CrMo tubing really needs a full heat treatment in an oven after welding and that is beyond most of us, so it is not the place to begin either.
Dennis

Dennis, I'm gonna have to disagree with you about the ERW tubing. There are a lot of rumors about it splitting and such.

I started working as an SCCA Tech Inspector in 1963. I switched to Offroad race Tech in 1973 working at the 1st SCORE race. With SCCA, it was my job to analyze race cars after crashes and write up a damage report in the log book for the car. After 50 years of Inspecting race cars, and having sat in on the discussions to write between my father and Mickey Thompson in our dining room to write the SCORE rule book, that same father having been instrumental in getting the SAE College Baja program going; and professionally fabricating race cars of many types, many of which have been quite successful in their type of racing, for 30years...I feel pretty well qualified to state that in all of that, I have NEVER seen an ERW tube in the roll cage or chassis of a race car or play buggy or any other sort of vehicle fail in the manner you describe.

I HAVE seen a LOT of fatigue crack failures in 4130 chassis. I HAVE had a customer's car I was maintaining collapse the bottom rails of that chassis upon banging it on the ground and then finding it was made of .049 wall 4130.

If I were writing rules for an offroad race organization now, I would be more inclined to agree with NASCAR and ban 4130 tube than to agree with Bill Savage and ban ERW.

To get back to the original poster's questions...the standard material over the decades in building VW-based offroad buggy frames and Baja Bug roll cages has by the vast majority been 1.5" OD x 0.095" wall 1010 alloy CREW tube. Many designs have included 1" x .065 wall "truss lacing" of the same material.

Over the past 50 years of offroad racing, it has proven to be safer than going to bed at night. If you doubt that...Ask how many racers have died from crashing their race cars vs how many of them have died in a bed! People playing often get hurt and/or die due to issues such as improper belts and not wearing them, no helmets, chassis and roll cages built without certain members such as a diagonal behind the driver, etc. But I have NOT seen the tubing fail as you describe in play cars either.

My own personal preference in cage and chassis material is DOM. But my own championship winning offroad race buggy and my own Baja Bug are both built with ERW.

In an offroad car frame or cage, 4130 is "Bling".

Sat Mar 15, 2014 9:04 am

All of my 7 or 8 cages are ERW "old school" stuff and your real world experience is great to know. I have "tested a couple of them" and had no splitting troubles either.
I hate it when I am caught out on junk science from the media and the overpaid experts. SCCA might as well be Global Warming fools.
Mostly, free advice means be careful on both ends, hence my repeating the "gospel according to SCCA" nonsense. Sorry.
Dennis

Sat Mar 15, 2014 5:50 pm

I have, they don't split on the seam, they split down the side in the HAZ, it's very rare but in the right circumstances it car happen, we had a competitor impaled by part of his own cage because of it back when our supplementary regs allowed it to keep costs down, that was hastily withdrawn and all cars need to be hydraulic-spec tube, CDS or better now.

Sat Mar 15, 2014 10:03 pm

Hmmm....

Hydraulic spec tube is not intended for structural use and is often quite maleable. eg it bends EZ. That's not what I would recommend for a roll over protective structure. English ERW may be different from that sold in the US. It's good for chassis and roll bar material to have some maleability, so it is less brittle than 4130, but too maleable is not good either.

I was just a couple of hours ago looking at some old photos from my SCCA Tech days of a roll bar sheared off a Formula Ford, a snapped roll bar in another Formula car and cockpit area structure failure in a frontal crashed D/Sports Racer. My wife had found them in the family photos. The Formula Ford reminded me that while oven brazing offers surprisingly high tensile strength (like 80,000psi, similar to 4130) in a joint, the shear strength and tear strength are not so impressive. And the photos show snap failures of 4130 in all 3 cars in chassis and roll bar structure.

We ARE wandering a ways away from the subject of the original post.

Sun Mar 16, 2014 1:36 am

I know our T45 spec is a bit better for both bending and welding than your 4130, but we've had a lot of big impacts with dozen of T45 cages, and I've never had one crack or snap.

I've seen a lot of cars made out of hydraulic pipe crack, but that's usually because where the T45 has enough elasticity to spring back from an impact, the hydraulic tube just bends a little and fatigues over the years - same as ERW would.
I know you say hydraulic tube is quite malliable, but over here it's still a lot stronger than ERW in terms of yeild strength, so it still makes a better cage than ERW ever would.