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Old 05-14-2011, 02:29 AM
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Richard K Richard K is offline
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Default Superleggera Coachbuilding Technique

"Superleggera" has become a fashionable word in today's world of supermarketing. The word commands some sort of reverence it seems, possibly because of its connectiveness to memorable automobiles emanating from Italian design studios of the 1930s to 1960s. The word has become detached from its 1930s reference to a specific autobody type.

CARROZZERIA TOURING SUPERLEGGERA S.r.l. Via per Arese, 30 20017 Terrazzano di Rho (Milano), the originator of the process, offers the advertising line below referring to a new design, GUMPERT TORNANTE by TOURING.
"Featuring composite body panels over the light chrome-molybdenum steel space frame with carbon fibre monocoque, the construction principle mirrors the original method patented by Touring in 1936, and authorizes the symmetrical Superleggera badges on the bonnet."

Superleggera (from Wikipedia)

Superleggera is an automobile construction technology used in Italy from the middle of the 20th century. The name means "super light" in Italian, and was coined in 1937 by the Italian coachbuilder, Carrozzeria Touring. Unlike the monocoque and body-on-frame methods widely adopted by the 1950s, Superleggera cars use a frame of metal tubes as a full-body frame which closely follow the shape of the car. These are then covered with body panels, made of aluminium alloy. The Superleggera frame tubes are too small and of unsuitable material for mounting suspension components. This distinguishes it very clearly from spaceframe construction where no separate chassis is required.
The Superleggera construction method was primarily based on the use of 'Duraluminium', which originated from the zeppelin industry before World War I. Carrozzeria Touring sold a Superleggera license to Aston Martin, who used it for their DB4, 5 and 6 models.[citation needed] This construction technique is no longer used in volume production cars today. Modern standards for impact resistance are the main reason, but the cost of the largely hand-worked coachbuilding is another factor. Corrosion resistance is another factor: where the dissimilar metals of the aluminium bodyshell and the steel tubes are touching, they will begin galvanic corrosion unless this is prevented, usually by intervening pastes or non-conductive shims. Car makers such as Bristol, who had past experience in the aircraft industry, were more successful in countering this corrosion than others.

David Gardenier offerred the comment below in another thread by Sollis on the Jaguar deck lid. I had suggested that the method used by Solis of forming the structure of sheet stock was a more workable plan than a tubing frame for the skin. I have seen many attempts to fabricate a frame of rectangular tubing and then weld the skin to the edges of the tubing. That method often results in warping of both frame and panel with no way to resolve the problem.


Richard, many coachbuilt cars had tubular frames for doors, boot, bonnet etc. (trunk, hood). some were built entirely with a tube framed body. for example Ferrari, AC, Alfa Romeo and Aston Martin. It can be done either way. What sollis has done here is quite difficult to achieve. To get all the angles and curves right from folded construction is quite a challenge. I thought I would just add that it is better and more common to use round tube. This is what is used on all the superleggera frames I have seen or worked on.
David


David is correct. as far as the tube framed body statement goes.

However, clarification is needed. There is more to the supperlegara process details. The tubing only supported the body; it was not what the body (aluminum) panels were attached to. I have found many photos showing details of the construction and I have looked in person at several examples (mostly Ferraris). In most cases (not all, see below) body panels are mounted to flanges, jambs, pillars and gutters which are made of sheet steel and then welded to the round steel tubing support structure. The result is that at the juncture of the exterior body panel and the subframe parts; the arrangement is very much like construction of standard formed sheet steel coachwork.

Deck or trunk and hood or bonnet openings were often framed in a formed sheet steel gutter welded to the support tubing. The gutter provided a weatherstrip or gasket seating surface, a drainage path for water and a means to mechanically fasten the exterior panels. The decklids and hoods often had the tubing main structure with a sheet steel flange welded on the outside edge. The deck and hood skins were often crimped onto the flange in a fashion similar to todays construction.

Door jambs also are familiar construction, as are window openings and the opening doors. The real difference is inside the car; the superlegara process utilizes the strength of light tubing in place of the bulky and heavier stamped panels we see most often.

The above is my understanding of what I have read and have observed. It is only a small sampling of the many automobiles that were produced in this manner. If anyone has other info or photos or whatever; it would be great to see a broader picture of this unique construction.

The most often noticed exception is on open cars, usually competition cars; the body panels at the cockpit or passenger compartment opening were sometimes wrapped around the support tubing. This gave a strong and rolled edge. This same sort of edge is sometimes seen in the wheel and grille openings.
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Old 05-14-2011, 08:27 AM
jmcglynn jmcglynn is offline
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Richard, very timely topic as I've been thinking about this method of construction the past few days myself.

I've seen cars done both ways in terms of the body being directly attached to the tubing and others where the tube had a flange welded on that the skin was hemmed over.

I'd love to see pictures of this construction technique. I tried googling for things superleggera but didn't find any relevant construction pictures.

Joe

Last edited by jmcglynn; 05-14-2011 at 08:58 AM.
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Old 05-14-2011, 09:01 AM
jmcglynn jmcglynn is offline
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There are some interesting pictures on Steve Moal's site. He did a scratch-built car called "Gato" that used this technique. It looks like he used a combination of tubing and flange methods.

The superstructure is a work of art. The complete slideshow of the car is here: http://www.moal.com/04_gallery/11gat....&currentPic=0

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Old 05-14-2011, 10:00 AM
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Kerry Pinkerton Kerry Pinkerton is offline
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This is another '...if I had only known...' thing for me. The roadster would have been much simpler to build had I taken a superleggera approach. If there ever is a follow on coupe version of the roadster, it will be superleggera.

One thing that has stumped me about wireforms is how you keep them from deforming at the weld joints. In my experience, the weld cooling pulls the arc. Making symmetrical 3 dimensional curves is hard enough.

Another good source of info is the Kirkham build diary.
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Old 05-14-2011, 11:45 AM
Ron Naida Ron Naida is offline
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[QUOTE=Richard K;34790[U].[/U]
snip
Deck or trunk and hood or bonnet openings were often framed in a formed sheet steel gutter welded to the support tubing. The gutter provided a weatherstrip or gasket seating surface, a drainage path for water and a means to mechanically fasten the exterior panels. The decklids and hoods often had the tubing main structure with a sheet steel flange welded on the outside edge. The deck and hood skins were often crimped onto the flange in a fashion similar to todays construction.QUOTE

I had an original AC in the shop to work on years ago and took some photos of the bonnet underside

Ron
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Old 05-14-2011, 02:50 PM
David Gardiner David Gardiner is offline
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Richard, I hope you did not take exception to my comment,, It was not intended to undermine what you said. I think I slightly misunderstood what you were saying. I pictured a tube frame with a flange welded on as is done on Aston Martins etc. I realise now you were saying just rectangular tubing.

I have made boot lids (trunk lids) in both ways and to make one from one piece of steel with just the corners added is quite tricky.

I have worked on several Aston DB4s over the years and they are not my favourite car to try and repair- everywhere you want to get your hand there is a tube.

David
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Last edited by David Gardiner; 05-14-2011 at 02:53 PM.
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Old 05-14-2011, 04:31 PM
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David,

No problem at all. In fact I'm glad you added on to the commentary. I had been thinking of posting some info and questions about different coachbuilding processes for a while.

This is a subject that discussed often, but in a sort of indirect way, as a part of some post that has its own focus. It is exciting to see some interest and potentially some photos and ideas.

We all gain in broadening our knowledge in various techniques.
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Old 05-14-2011, 06:11 PM
Paul Aitchison Paul Aitchison is offline
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Fantastic, This is exactly what I was after when I posted a while ago "Supports and attaching" and was cautioned for being 'off topic'
More pictures please, I need ideas.
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Old 05-14-2011, 07:35 PM
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I do metalwork for a Aston Matin specialist restoration shop, been there for 4 years now, and have learned more than I care to about these cars and their construction. DB-4, 5, and 6 are not easy, and require a majic wand from time to time, but I'm always amazed at how well(for a handbuilt car) the craftsmanship is. The welds are virtually invisible and not filed to death either, although the guy who was in charge of welding the bonnet scoops on straight...well lets just say he was unsupervised
I just completed a DB/4 that had front and rear collision damage and an engine bay fire! I had to recreate both areas, then tackle the normal restoration spots, glad it's in the bodyshop now.
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Old 05-15-2011, 03:48 AM
David Gardiner David Gardiner is offline
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Max I empathise completely with you. The superleggera construction methods are great for constructing a car but if it needs a repair the only way to get at the panels properly is to deconstruct large sections from the frame, not something that the customer wants to pay for.

The welding on these cars is superb as I have said on here before. The results they get are hard to match but I guess they were welding these panels all day every day. All the aluminium welding done on these cars was gas welding.

There are many Aston Martin trained guys working in the restoration industry here in the UK. There are also a lot of guys trained at AC and Rolls Royce doing restoration work now. I know of several.

The frames on the DB cars are very crude and some of the tubes dont seem to do much especially the ones around the rear valance area.

Slightly off subject but for those who don't know the DB cars were built during the period that Aston Martin was owned by David Brown (DB).


David
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Last edited by David Gardiner; 05-15-2011 at 03:58 AM.
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