Just dreaming: Aluminum C3 frame. Input?

bigbrother said:
If i were able to fab an aluminium frame, id use 7075 aluminium.
I use 6061 aluminium frames on my rc cars. They bend often. Because of the greater cost, no one offers 7075 frames.
However there are chassis upgrade pieces in 7075 and those are usually half as thick as the t6061 pieces and just as strong.

Sent from my dumb 4g motorolly
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I used to build displays for trade shows - we never used 7075 because it has to be forged, it can't be bent as it's too brittle. I never tried annealing, but if you anneal it, you might as well use 5056.
 
Grampy said:
Ideally the chassis should be a stiff as possible. This design goal is usually expressed in torsional stiffness. The C3 has some severe constraints with the basic body on frame architecture and ladder frame. Aluminum is about 1/3 the weight of steel. Some alloys like 2024 and 7075 can be stronger (higher tensile strengths) than the OE low carbon steel frame material. These stronger alloys come with fabrication and corrosion issues. The larger issue is that aluminum is also only about 1/3 as stiff as steel. To replicate the OE frame in aluminum would produce a very flexable piece. Working with aluminum, if you wanted to keep the same basic design you would have go to larger sized members to regain the stiffness but there is not room to do that in a C3. Simple increases in wall thickness are not efficient and won't save the desired weight. To be successful the aluminum chassis would have to be more three dimensional like a tube frame car or the newer C6/7.

Grampy
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I agree.
I've got the original rolling frame sitting in the corner of the shop, and I take a glance at that thing every time I'm out working on the cars. It seems that a person could take a few liberties regarding the shape of the final product. Larger diameter tubing could be used in several places, as the lowest points on my car seem to be the oil pan and header flanges, not the frame. There's also a few frame bends that don't seem to require that sharp of an angle to clear stuff, and could be moved around a bit. It seems some larger OD tubing and a few extra selective struts/crossmembers/shearplanes could regain some of the stiffness lost from the change of material.
On the stress cycle side, my car is driven on mostly smooth roads and tracks (and certainly less miles per year than an OTR truck), so I think the fatigue issue should hopefully be easily managed.
IIRC, the stock frame weighs about 280-300 pounds. It would be nice to be able to build a substitute in the 200 pound range.
 
I keep thinking the lightest would be to copy a stock-car chassis in aluminum... but I won't know the answer to that question until the Buick build - which may have been delayed again
 
When I strip my 90 frame I will weigh it. I can tell you the rear B pillar metal is pretty heavy as was the A pillar metal.

But I say when the frame is stripped it will be lighter then a C3 frame.
 
bigger might work but 3D is better

The flexability of a simple element is governed by the material and shape. In real simple terms aluminum has 1/3 the stiffness of steel so to stay even the shape must be 3 time stiffer. We get some help here as the stiffness increases with the 4th power of the tube diameter. The main frame members are sorta 4.5 by 4.5 boxes something around a 6 in dia alum tube with little thicker wall would have a moment of inertia about 3 times bigger. The frame is more complex than a simple member and the best solution is to go 3D with a tube frame like SBGs picture.

If you look at Cannondale's alum bicycle frames you can easily see they used large dia tubes to make avery stiff light weight frame.

Back in the 60's there were some very light weight alum space frame sports racing cars called Bobsy's. I think they eventually ran small blocks.

I believe from some of your other posts your objective is to keep the upgrades stealthy so 3D might not be to your liking but try and think how to hide the cage tubes.

Grampy
 
Well, It would be more expensive - but - why not go ALL Out and build a space frame (probably the easiest to design and model) -- out of Carbon Fiber tubes?!!
Now - THAT would really be something!

Sorry, the comments about Cannondale bike frames made me do it.
Cheers - Jim
 
phantomjock said:
Well, It would be more expensive - but - why not go ALL Out and build a space frame (probably the easiest to design and model) -- out of Carbon Fiber tubes?!!
Now - THAT would really be something!

Sorry, the comments about Cannondale bike frames made me do it.
Cheers - Jim
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aluminum has one advantage over carbon fiber that ends the analysis, IMO.... with an aluminum frame, what is bent can be bent back. With carbon fiber - what is broke stays broke. I know, I'm on my 3rd carbon fiber bike in 5 years for that very reason.
 
SuperBuickGuy said:
phantomjock said:
Well, It would be more expensive - but - why not go ALL Out and build a space frame (probably the easiest to design and model) -- out of Carbon Fiber tubes?!!
Now - THAT would really be something!

Sorry, the comments about Cannondale bike frames made me do it.
Cheers - Jim
Click to expand...

aluminum has one advantage over carbon fiber that ends the analysis, IMO.... with an aluminum frame, what is bent can be bent back. With carbon fiber - what is broke stays broke. I know, I'm on my 3rd carbon fiber bike in 5 years for that very reason.
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OLDE TYME motor head demands all sorts of PIX and information please, just for shits and giggles....THAT is interesting stuffs man......new thread ......:loveletter::stirpot::cool:
 
Finished putting in the new aluminum brackets for the under radiator crossmember, and took a look over the car for any additional items to swap out for lighter replacements. A couple items caught my eye. The crossmember behind the batwing seems to be a lightly loaded item that could be swapped out for an aluminum piece. I should have done that years ago when I was working on the suspension swap, but I didn't know how to weld aluminum at the time, and the suspension swap was going slow enough anyways. I'm now trying to figure out if it's worth just replacing the crossmember, or cutting out the whole rear of the frame behind the batwing and making a bolt-on replacement, similar to the C4 part.
 
You know, that'd be a really smart thing for me to do right now - the major advantage (IMO) would be that I could better fit the sway bar.... I'm thinking cut at the differential mount and replace that entire area.... good idea man :thumbs:
 
I'm going to say the c4 frame without "a" & "b" pillars out weighs a c3 frame. I cut my frame apart today and each section in front of the doors and then cut in half in the back are incredibly heavy. Took a dolly to move each section put it that way.

I will weigh the sections tomorrow but a rough guess at the full frame weight would be around 400lbs. With the a & b pillars probably 500lbs.

here is where I am at now on cutting it up, contrary to what everyone I talked to the rear suspension doesn't flop around without the dogbones attached to anything.

framechop005_zpsaff1ffe3.jpg
 
Okay, I weighed each frame rail. Each weighs right about 125lbs, the rear aluminum bumper tank support weighs another 38lbs. No idea how much the front frame rail section weighs yet though.

These weights are without the metal floor pan or riser, and without the a & b pillar.

I would venture to say a complete bare C4 frame would weigh about 400-500lbs
 
Well, this thread has gotten a few cobwebs since the last activity, but I still haven't lost interest in the subject. I picked up some rectangular aluminum tubing last week to make a replacement transmission crossmember (and possibly to replace the rear crossmember behind the batwing). IIRC the stock steel transmission crossmember weighs 22 pounds. I drilled several holes in it years ago, but only got it down to 20 pounds. I'm going to fabricate a new crossmember in an effort to lose a few vehicle pounds (although this particular weight loss will be a little "less efficient" due to the low and centered position in the car).
I have no idea how much weight the present crossmember holds so I might jack up/support the transmission with the jack sitting on a scale to get an indication of the load, then put in a fudge factor to simulate the car bottoming out in a dip in the road or track. After welding up the new crossmember I can make a test stand and load the crossmember with some weights and measure the deflection with a dial indicator. I'm not sure what non-zero deflection amount is acceptable, but I feel better if I at least have some idea of the stiffness of the part. If my thinking is way off please set me straight.
 
The module of elasticity on alu is around 70000N/mm2 and for steel it is approx 210000N/mm2. This means that the alu crossmember will flex alot more compared to the steel unit. You would have to increase it's dimension basically 3 times to get the same stiffnes.
You probably already knows this and that is why you are set on testing the design. It will be interesting to see how stiff you can make it, perhaps with a smart design you can get there!

Regards, Daniel
 
JeffP1167 said:
I think you would find much what I did when I considered using the frame from my C4. For one it's wheel base is 1.8 inches shorter, Then the frame rail area under the doors is about 3.5 inches wider then a C3 frame.

however I wonder if the frame rails were moved in, then do a 1.8 inch stretch & trim and reinforce the A & B pillar areas if a C4 frame could fit under a C3 body.

The C4 frame has the same basic shape as a C3 frame but seems to be much stronger. As for weight I am not sure of the rolling C4 frame.
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The C4 frame is thicker than the C2/C3 frame and galvanized. Dave McLellan's book says that they had to come up with some rather novel methods of welding to build them.
 
My only comment is that aluminum tends to shatter like glass when subjected to vibration stresses, happened on one of my fab up jobs on a FI sender unit on a Volvo engine boat, years ago....went steel instead to solve the problem....

then later on, the '72 here developed a stress crack in the a/c comp bracket....missing bolt on the pass side head, got it TIG'd and then put on a L bracket to the front manifold bolt.....

I"d be PAIR A NOID over an aluminum chassis.....


:tth::crutches:
 
I just watched "dream cars, how it's made" - look at that show, specifically, the Jaguar one for ideas on how to make it happen....
 
think outside the square

I'm just embarking on a project I'm calling 'project C36', codenamed "The Hammer".

This involves starting with a salvage C6 Z06, stripping all the body panels off, and retro fitting a heavily modified '68-'69 convertible body ontop of the Z06 platform.
Yes, it's a big job, yes also this approach would not be possible if you crave a standard body, but it is doable.

I saw this as an opportunity to give the C3 a more contemporary design twist in our endeavours to get the C3 body to work with the C6 frame.

Our goal is to end up with a modern supercar driving experience with a hottrodded C3 body.

We've just got started, but progressing well. Just finished a similar project using a C2 coupe body ontop of a '03 C5 Z06. Check out if you wish on www.prodigy-z06.com

If you really want a modern car driving experience with contemporary / classic lines, it's an approach I'd recomend, and not yet seen tackled by anyone else.

Something to ponder????
 
aussieross01 said:
I'm just embarking on a project I'm calling 'project C36', codenamed "The Hammer".

This involves starting with a salvage C6 Z06, stripping all the body panels off, and retro fitting a heavily modified '68-'69 convertible body ontop of the Z06 platform.
Yes, it's a big job, yes also this approach would not be possible if you crave a standard body, but it is doable.

I saw this as an opportunity to give the C3 a more contemporary design twist in our endeavours to get the C3 body to work with the C6 frame.

Our goal is to end up with a modern supercar driving experience with a hottrodded C3 body.

We've just got started, but progressing well. Just finished a similar project using a C2 coupe body ontop of a '03 C5 Z06. Check out if you wish on www.prodigy-z06.com

If you really want a modern car driving experience with contemporary / classic lines, it's an approach I'd recomend, and not yet seen tackled by anyone else.

Something to ponder????
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I'm very interested in what you're doing on this latest project, and would like to see pictures as you progress, but unfortunately the basic premise here won't work for my application. I do a lot of track days with my car (so I enjoy having a modern suspension) and as I've mentioned before I like the stock lines of a C3. Hence I am (self) restricted to making chassis and weight improvements that are invisible to the casual glance. If I make significant changes to the bodywork it then starts to look like a modified/race car, and modified/race car speed and performance is expected by the competitors. I've found it's a lot more "amusing" when competitors scratch their head wondering why my stock looking antique is either keeping up with them in their newer cars, or making them work to pass me.

Good luck with your project, and I look forward to seeing pictures of it.
 
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