Frame Tubing Rollers?

[fritts]

I really wasn't sure where to put this post so mods please move it if this isn't the right place. I would like to understand how the long radius frame tubing is being rolled? The tubes I am talking about would be similar to the two main frame tubes on the Atom or even the SLR. Are there vendors that can supply cnc bent long radius tubes to specs? If possible could we get a list of who has these type of capabilities? I am working on my own miata suspension geometry based Exo and am trying to figure out how I could get the long radius frame tubes bent accurately. I have fiddled around with using plywood forms and my oxy torch but figured that with the CNC rollers available someone had to be doing this tubes in a better way.

[JonW]

I never did an exhaustive search for a vendor with a CNC roll bender. I would rather make my own tool and roll my own (just like the '70s). It cost me about $130 IIRC to make my bender. It bent 2" dia, 16 ga, DOM.

You can buy a manual bender from Eastwood. Google (Tubing Roller). They are about $1000 last time I looked. They come with 1, 1.5, and 2" rollers.

[fritts]

Where did you get your rollers and what did you do for your bearings and adjustment screw?

[JonW]

I first turned three oak rollers. After the top one failed, I turned a new aluminum top roller from billet. Needle bearings were from recycle yard at $.50 per pound.

See: http://www.locostusa.com/forums/viewtopic.php?t=1503

There's another Atom "tribute" build there also.

[fritts]

Looks like Harbor just came out with one.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=99736

[FIAROADSTER]

Ariels are the only car I know of that use a compound curve as part of the main frame. Some cars use curved elements to hang body skins on (Cobras for instance), but they are not really structural. You just don’t see this in a Birdcage or a Mercedes Gullwing. There must be a reason for this.
Why use a tube that is technically difficult to form (expensive) and more difficult to place (multiple arcs) when straight tubing with common bends is stronger and cheaper? Tube frame dune buggies have been using the exoskeleton for decades. They have proven the design in extreme off road races. It works. Nothing but straight tubes and simple bends. The concept behind exocars and buggies is the same. They differ in suspension and engines and purpose, but that’s just details. The concept is the same.
Is it just because that’s the way Ariel did it? Style maybe?
Seems like imitation in this case is poor engineering
Rick

[fritts]

I would like to imitate the frame to a degree. It has a sort of elegance to it that separates it from the average "dune buggy". Style is always part of a form whether you like it or not. Poor engineering, I think that's a bit harsh as this vehicle for me is not going to be a track only vehicle where all out might matter.

[Karlo]

Looks like Harbor just came out with one.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=99736



it is amazing how inexpensive that tool is!!

[#Rotor]

those curved tubes.... looks only.... that is all they are there for.

It is structurally not a good idea to use bent or curved tubes in a frame, unless it somehow forms a safety aspect of the frame, such as a kind of crumple zone, of sorts.

I have mine CNC'd by a place, 2mm gauge and 60.3 mm in diameter, it's a bit of a problem doing that by hand.... :)

[JonW]

Is it just because that’s the way Ariel did it? Style maybe?
Seems like imitation in this case is poor engineering
Rick[/QUOTE]

Although I haven't done the FEA (I leave most engineering at the office), I believe the curved tubes offer, relative to side impact forces: increased strength (arch-shape) and crush space. Besides, compared to a Lotus 7 clone (1" sq. 0.065") design, the 2" dia x 0.065" wall DOM tubes are greatly oversized. It's the styling.

Sounds like you won't be building one or buying one then?

[Exonut]

That Harbor Freight tube roller won't do much good for building an Atom-type frame. It's capacity is only 1.25" and even with a set of custom rollers it looks like 1.5" is the max. It surely won't fit the 2.25" tubes of the Atom. It also has only one driven roller which could cause some touble. Every other commercially available tube roller I've seen has two driven rollers.

[bolus]

those curved tubes.... looks only.... that is all they are there for.

But the two major crashes we have seen the passengers survived.

The Dutch crash the Atom went sideways into a telephone pole at a high rate of speed. The frame absorbed the crash and the drivers leg was broken though this was right at the site of impact. (I cant report pics of this but it is in the clubroom on the atom site)

Then the other was was the head on crash into the brick wall. I'm no structural engineer but these look like they held up well

[#Rotor]

damn that picture is painful to look at...

In my efforts to become wise, with regards to building space-frames, I was forced to turn to the locost lotus guys, they where unfortunately to only ones friendly enough and willing enough to share their knowledge, some of them, respected engineers and all, had some convincing arguments against using curved tubes in a frame, where the main aim is to save weight and gain rigidity.

Those 4 main tubes being curved, forced their diameter and gauge to be extremely over-engineered, just to be rigid enough for normal use, and in so doing the safety aspect of the frame got a very welcome and completely unintentional boost.

I can assure you Mr. Smart did not choose them for rigidity or safety... only for esthetics and visual effect. the rest was all winning the lottery.... :)

[bolus]

just saying, they may have not been designed for the best support but these unofficial crash tests show they worked out pretty good regardless

We have this discussion on the atom forum a lot. At some point you have to give up some safety to drive one of these cars because there is no way to make them 100% safe. You can over engineer all the safety you want in them but you are still going to be in trouble if you hit a brick wall at 100mph.

[#Rotor]

I fully agree... and at the end of the day, being in a doorless roll-cage.... worth all the air-bags you can fit....

I always say that if it's a man's time to go, he can be in a tank, it won't help him one single bit...

[fritts]

those curved tubes.... looks only.... that is all they are there for.

It is structurally not a good idea to use bent or curved tubes in a frame, unless it somehow forms a safety aspect of the frame, such as a kind of crumple zone, of sorts.

I have mine CNC'd by a place, 2mm gauge and 60.3 mm in diameter, it's a bit of a problem doing that by hand.... :)

Who is your source for bending?

[#Rotor]

it's a local company "Indent Manufacturing"

[cheapracer]

Try your local goverment public works department, most likely they have/know contractors to do handrails, streetlamps, public park stuff etc. which sometimes are curved in long radius.

[cheapracer]

How my local Chinese Guys do it, maybe you can draw some ideas from their machine.

Ugly but it works (the machine not the operator).

[Karlo]

No frills but in the end it works :thumb2: