Steel VS Aluminum for a frame

My engine is aluminum and I started to think about building a Frame out of square aluminum tubing. My Miller wire feed can weld aluminum so it should be within my capability.

I know the first batch of D type Jaguars had an aluminum sub frame but they later went to steel and reduced the weight by something like 22 pounds while making the frame much easier to repair.. On the other hand steel cannot be polished up the way aluminum can and needs to be painted... Plus to really take advantage of steel's strength It probably should be T.I.G. welded which I don't have anymore..

I also want to use some of 3M's adhesive for aluminum. The spec sheet is impressive plus I tried to pull a couple of sheets of aluminum apart that had been glued and the aluminum tore before the joint ever yielded.. Besides since this will be a Vintage tribute car I'd finally get to use up a significant portion of those aluminum rivets I acquired in my Navy Years..

Im sure that there are many thoughts here, but these are my first impressions

• MIG will not get the penetration on aluminum necessary to be structural
• Aluminum is much more expensive
• Aluminum fatigues over time much worse than steel
• Adhesive "feels" like the wrong way to go (I know... modern cars are glued together)
• If you do use aluminum it will need to be a monocoque (for strength), not just a frame.

frenchyd wrote: Plus to really take advantage of steel's strength It probably should be T.I.G. welded which I don't have anymore..

This is not true. A good set-up MIG (that is getting proper heat penetration) will be plenty strong for a car chassis. Almost ALL Locost frames are done with MIG. I have yet to hear of a frame failure when MIG welded properly.

If the "polished" appearance of Aluminum is what attracts you, consider Stainless Steel?(maybe?)

Sounds iffy. Mig+aluminum isn't a great idea for structural stuff because you can't control the heat as well, and aluminum is very sensitive in that regard because it conducts heat away from the weld so well. You'd be much better off MIG welding steel for a frame.

Aluminum fatigue life would be a concern - making sure that your F.O.S. is adequate suddenly becomes much more critical, and you have to stay somewhat lower on the stresses in the part to ensure adequate life. This usually results in a larger part, which may or may not be lighter than steel. Mass-produced vehicles get around this using complex castings and FEA to verify the design.

I'd be interested in seeing more on the adhesive, but I don't know enough about it to say if it's reasonable for a frame or not.

I'm not saying it can't be done, but it will take much more work than building a steel frame and having it powdercoated.

Just so you know, wherever Lotus glues aluminum they also bolt it, they never use glue by itself. McLaren's recent supercars use a combination aluminum & CF unibody so that's another example worth looking at.

glue it together. Lotus glues their cars together as do Jag and a few others.

Ditch the welder and avoid heat effected zones and glue it.

You will need sandwich gusset plates on both sides to get good adhesion and strength.

To be honest with a proper design glued 6061 is tough to beat. Especially if you are not an expert welder. I don't care if it is steel vs aluminum. You screw up a weld, it looks great up until it fails. You clean and prep the adhesive correctly no worries.

I don't know about you but I can clean and mix better than I can weld.

GameboyRMH wrote: Just so you know, wherever Lotus glues aluminum they also bolt it, they never use glue by itself.

The bolts have nothing to do with the strength of the car as they are used to hold the parts together until the adhesive cures. Lotus actually found that 0.2mm standoff's are best as that is the optimal glue thickness for best strength.

Lotus has place extra bolt holes in the structures around areas that are possible damage points to allow retaining bolting of new reinforcement plates to allow glues to cure in the repair shop.

In reply to frenchyd:

You are not the only person looking into this idea on this board. Maybe there is an engineer converting a current weld up car to sheet aluminum and adhesive design because he can't weld for E36 M3 and doesn't like the time it takes to cut and weld all those tubes. Just saying.

Semi-monocoque locost type build:

http://locostusa.com/forums/viewtopic.php?f=36&t=10658

lotta pics and details... and appears a ton more work than a tubular steel chassis.

Not quite the same thing, but Trek was gluing together aluminum bikes back in the late 80's. They called them "bonded aluminum" if you want to research how it was done. Still, I think a combination of glue, rivets, bolts and/or welding might be more prudent.

Not that you or anyone reading this thread is interested, but that whole bonded aluminum gave Trek an advantage working with carbon-fiber which came soon after and changed the bike industry. Carbon fibre bike frames were basically glued together, and since they were already gluing together their aluminum frames they were able to use that to be one of the pioneers in CF.

So who knows, maybe if you master aluminum your next locost could be homemade carbon fiber.

In reply to SEADave:

I think that is cool. Since the adhesive is a major component of the functionality of the frame it makes since that they get a leg up on FRP construction.

Learned something new today.

Oh yeah which 3M adhesive are you looking at?

If using adhesives, why stick to tubes (be they round or square)?

This book has some very basic information about building a honeycomb monocoque chassis. http://www.amazon.com/Build-Motorcycle-engined-Racing-Cars-SpeedPro/dp/1845841239

Only thing is that repairs are more difficult and you would have to look closely at racing class information for eligibility. Usually they require the safety structure to be steel and by the time you figure out joining the steel safety structure to the aluminum chassis parts you might as well have done the whole thing out of steel to begin with.

What exactly is the fab skill level of the OP? MIG experience on steel is not anywhere near equivalent to MIG on aluminum tubing, TIG would be the preferred choice and only then w/ lots of experience on chassis or components. Semi-monoqoque would be second choice for weight savings but only w/ strict guidance from say a airframe mechanic or engineer in design and fabrication, this ain't no backyard build E36 M3 whether a street or HPDE car.

Basic MIG welded steel frame is totally attainable. OP, save those aluminum rivets for the downspouts.

In reply to Apexcarver:

I have read a few chapters in that book. Good stuff. As far as the cage you could build it to FIA rules so you won't have to worry.

Id just go steel. The ease of assembly is more than worth any disadvantages.

IndyJoe wrote:

frenchyd wrote: Plus to really take advantage of steel's strength It probably should be T.I.G. welded which I don't have anymore..

This is not true. A good set-up MIG (that is getting proper heat penetration) will be plenty strong for a car chassis. Almost ALL Locost frames are done with MIG. I have yet to hear of a frame failure when MIG welded properly. If the "polished" appearance of Aluminum is what attracts you, consider Stainless Steel?(maybe?)

Well the right steel (4130) can be lighter than aluminum but that does not factor in the weight of the powder coat or paint. The last frame I painted took nearly 2 quarts so perhaps once that is factored in the difference becomes pretty minimal?? However 4130 should be T.I.G. welded and I no longer have that welder, and the idea of buying another for one final project is beyond my retirement budget.

As for Stainless steel, it is both heavy and soft.. (at least the last time I checked)

NordicSaab wrote: Im sure that there are many thoughts here, but these are my first impressions - MIG will not get the penetration on aluminum necessary to be structural - Aluminum is much more expensive - Aluminum fatigues over time much worse than steel - Adhesive "feels" like the wrong way to go (I know... modern cars are glued together) - If you do use aluminum it will need to be a monocoque (for strength), not just a frame.

The Miller I have isn't the 110 volt model rather the 220 with plenty of ability to generate enough heat to properly penetrate.

I tend to buy aluminum in surplus stores. There the price is much lower and I've had very poor experience buying the high strength steels at the same locations. Thus they tend to equal out price wise..

Fatigue is a subject we can have some serious debates about. Airplanes made of aluminum seem to fly a very long time and I'm certain far more critical than a chassis that is used for a few autocross events a year.

As for Monique, Jaguar back in 1955 built their square tube front sub-frame out of Aluminum and connected it to the Monique. The cars held up well in the 24 hours of Le Mans

I'd use the adhesive in a belt and suspenders approach like Lotus does. We aren't talking about Yellow carpenters glue here either. Rather a properly engineered adhesive designed to connect aluminum..

I had some 2 piece wheels on a B production Corvette that used an adhesive. They held up without failure in spite of glowing hot brake disks and the weight, power, and impact of racing.. I attempted to change the offset and removed the bolts.. My 50 ton press and heat failed to budge the joint.. It took a 100 ton press and two rose bud acetylene torches to break the bond..

Flight Service wrote: glue it together. Lotus glues their cars together as do Jag and a few others. Ditch the welder and avoid heat effected zones and glue it. You will need sandwich gusset plates on both sides to get good adhesion and strength. To be honest with a proper design glued 6061 is tough to beat. Especially if you are not an expert welder. I don't care if it is steel vs aluminum. You screw up a weld, it looks great up until it fails. You clean and prep the adhesive correctly no worries. I don't know about you but I can clean and mix better than I can weld.

GameboyRMH wrote: Just so you know, wherever Lotus glues aluminum they also bolt it, they never use glue by itself.

The bolts have nothing to do with the strength of the car as they are used to hold the parts together until the adhesive cures. Lotus actually found that 0.2mm standoff's are best as that is the optimal glue thickness for best strength. Lotus has place extra bolt holes in the structures around areas that are possible damage points to allow retaining bolting of new reinforcement plates to allow glues to cure in the repair shop. In reply to frenchyd: You are not the only person looking into this idea on this board. Maybe there is an engineer converting a current weld up car to sheet aluminum and adhesive design because he can't weld for E36 M3 and doesn't like the time it takes to cut and weld all those tubes. Just saying.

You make real sense.. plus I like the gussets except for the "pop" rivets.. I'd rather use solid rivets than "pop" rivets and not worry about the weak center where the mandrel was pulled from.. Perhaps I'm not thinking properly and the purpose of the "pop" rivets is merely to assure alignment during adhesive dry up?

I do like the way Jaguar overlapped the square tubes creating a much larger surface for connection and greatly increasing the number of Triangles.. Look at an XK-E front sub-frame for an example of what I'm talking about.. The 1 inch square tubes are thinner than sheet metal and yet on a frontal impact at 45 MPH The XK-E had no trouble passing a factory Crash test in the 1960's

fasted58 wrote: What exactly is the fab skill level of the OP? MIG experience on steel is not anywhere near equivalent to MIG on aluminum tubing, TIG would be the preferred choice and only then w/ lots of experience on chassis or components. Semi-monoqoque would be second choice for weight savings but only w/ strict guidance from say a airframe mechanic or engineer in design and fabrication, this ain't no backyard build E36 M3 whether a street or HPDE car. Basic MIG welded steel frame is totally attainable. OP, save those aluminum rivets for the downspouts.

The planes I flew in the Navy during Vietnam were all riveted together. General aviation still does. Yes I know the difference between solid rivets and "pop" rivets.

My skill level? Well cars I've built have been pretty successful. I once beat Sr. Stirling Moss in my BlackJack spl. Granted it was an Autocross event and His longer, wider, Aston Martin DBR3 was at a disadvantage. I should confess that I finished second overall To Sr Moss in the 1986 Vintage Grand Prix in the Bahama's. I couldn't keep him in sight on the race track.

Apexcarver wrote: If using adhesives, why stick to tubes (be they round or square)? This book has some very basic information about building a honeycomb monocoque chassis. http://www.amazon.com/Build-Motorcycle-engined-Racing-Cars-SpeedPro/dp/1845841239 Only thing is that repairs are more difficult and you would have to look closely at racing class information for eligibility. Usually they require the safety structure to be steel and by the time you figure out joining the steel safety structure to the aluminum chassis parts you might as well have done the whole thing out of steel to begin with.

I've made a few Carbon Fibre parts for race cars including the bonnet on my series 3 XK-E V12 and I'm tempted to do a whole chassis.. (I have a few rolls of it in the shop) but the car I'm thinking of doing wouldn't look right......

I want to do a Vintage car on steroids sort of thing.. M.G. T.C. Meet Jaguar V12 XK-E. I'm torn between using some 19 inch wire wheel wheels or Knock-off Pin drive magnesium wheels Cast by Halibrand for Troutman and Barnes Riverside spl. later known as the Chaparral Mk. 1

Eligibility? Ha!!!!!

Fitzauto wrote: Id just go steel. The ease of assembly is more than worth any disadvantages.

Who wants easy? Anybody can do easy. This is likely to be my last build.. (I'm 68) I want a statement car.. OK so it might not be most peoples sort of statement but I've never danced to normal..

In reply to frenchyd:

the rivets in the picture are structural but the set up I was speaking of wouldn't be. The photo showed gussets, tubing and rivets to hold, even if there are too many.

3 out of 4 ain't bad.

I find it funny how people, on this board, are knocking you going a different path. Yes, steel can be lighter than aluminum construction IF you design to steels strength. Yes, aluminum construction can be lighter and stronger than steel, IF you design to aluminum strengths. No, modern properly designed aluminum structures don't fatigue fail. That is when you design aluminum like you do steel. Welding aluminum has always been a bad idea, people just design around the heat effected zone. Modern adhesives fix this problem. No this isn't elmer's school glue. This is structural, toughened adhesives that are already holding cars you own together. Yes it works better because no only does it eliminate the heat effected zone it spreads the connection over a larger surface area. Follow the directions and you will be fine.

If this is going to be a statement piece I say damn the guns and ramming speed.

I applaud a 68 year old realizing what modern building practices are when young whipper snappers are saying can't be reasonably done.

Remember, there are complete plastic track day cars out there, using 10 year perfected tech instead of 60 year old perfected tech isn't ground breaking, it just isn't stone age.

frenchyd wrote: Who wants easy? Anybody can do easy. OK so it might not be most peoples sort of statement but I've never danced to normal..

So you just answered your own question. You do have the main tool required to do this build. Looking forward to the fist cut.

Flight Service wrote: In reply to frenchyd: the rivets in the picture are structural but the set up I was speaking of wouldn't be. The photo showed gussets, tubing and rivets to hold, even if there are too many. 3 out of 4 ain't bad.

I'll dig up my books on riveting before I settle on a particular pattern. I do realize the use of Buck Rivets takes a lot of clever preplanning to ensure the access and retrieval of the mandrel. Aircraft Spruce has some great books on the subject..

Flight Service wrote: I find it funny how people, on this board, are knocking you going a different path. Yes, steel can be lighter than aluminum construction IF you design to steels strength. Yes, aluminum construction can be lighter and stronger than steel, IF you design to aluminum strengths. No, modern properly designed aluminum structures don't fatigue fail. That is when you design aluminum like you do steel. Welding aluminum has always been a bad idea, people just design around the heat effected zone. Modern adhesives fix this problem. No this isn't elmer's school glue. This is structural, toughened adhesives that are already holding cars you own together. Yes it works better because no only does it eliminate the heat effected zone it spreads the connection over a larger surface area. Follow the directions and you will be fine. If this is going to be a statement piece I say damn the guns and ramming speed. I applaud a 68 year old realizing what modern building practices are when young whipper snappers are saying can't be reasonably done. Remember, there are complete plastic track day cars out there, using 10 year perfected tech instead of 60 year old perfected tech isn't ground breaking, it just isn't stone age.

I don't know if I can claim modern building practice.. Built in late 1954 The D type Jaguar race car chassis is the inspiration I intend to follow. 60+ years ago and they only built the first batch that way.. OK the Use of adhesives might be a bit newish but I was running on glued together 2 piece wheels nearly 30 years ago and recognized it's strength.. Plus the 3M factory is nearby and I got to know a few of those brilliant engineers..

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