How did they get from clay model to steel panels?

[Mark Norris]

As an engineer there is something often I've wondered about regarding car body manufacture ...how did they go from hand carved clay model to the heavy sheet stamping dies for the body panels. This is a very big step that seems to get completely overlooked. Obviously these days its done with 3D scanners and digital machine tools etc. but how was it done in the 1950s?

I've often wondered if its got some to do with this picture of the Mkii in development (which I think Barry W. originally posted);

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It looks like a massive plaster cast is being made of ...what ...the clay body model? Is it the first step in moving from the full size clay to something that can be cut up to make make individual "dies" from and then used to make molds for die copies in steel within a foundry?

If its not then what on earth are the modeling department upto in the photo?

Having said all that here are the front fenders mocked up in wood by a pattern maker and being measured on the surface table;

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Does anyone know how it was done ..if so please educate us.

[Barry Wolk]

The first picture is making the mold for a fiberglass roller of the Mark II.

I have never seen the wood models. These are used as reference for making steel dies. There are sometimes many different dies used to stretch the metal into its final shape. Die making is a trade unto itself. We were in a BMW plant in Germany that made the 7-Series. I believe there were 7 presses in a row dedicated to cutting and forming a single roof.

[Mark Norris]

Oh, so that's what is going on, yes, makes sense.

I did in the mean time find this;



..which describes the process of measuring the full size clays then smoothing out the shapes on a computer and doubtless getting them symmetrical ..all in the 1970s. It implies the process was similar but all by hand with a pantograph before that.

Agree, the metal stamping process has to be be done little by little with a series of machines especially for complex shapes otherwise one gets "Luders Bands" where the sheet metal bends not in a smooth curve but in a series of stepped flats. Its also the reason the sheet metal has to come straight from the mill so its had no opportunity to age harden.

The process of moving from the clay model to the assembled body in sheet steel is something that's just not given the level credit it deserves.

[Roger Zimmermann]

Thanks for that video! We could think that every vehicle is perfect when going out of the assembly line, but they are not! On my '72 Coupe de de Ville, there are several dents from inside out which were obviously done during assembly...

[Mark Norris]

Well despite searching the web I couldn't find any meaningful information on exactly how they transfer the complex shape of the clay model into the surface shape of the dies. Its my understanding the dies were cast steel then were rough machined by a pantograph guided from the clay before being fine finished by hand. Naturally the car bodies were then only as symmetrical as the clay body. Obviously on top of this they needed to work with the blueprints for the panels to arrange the flange locations for welding one to the next, door locks, hinge locations, trim fastening etc. etc.
Anyway, as Barry mentioned, even to this day honing (almost literally) the die contours is a very precise and skilled manual business to ensure the relaxed sheet sheet is in the right shape and is free of blemishes;



Glad to see they removed the die from the press before they started fettling it!


The stamping presses themselves are quite complex too, here's more than you ever wanted to know;

[Barry Wolk]

I believe you answered that. Similar to CNC in that respect they use a pantograph with a mill to shape the metal.

[Mark Norris]

Well after some more searching finally here is the technique in the flesh ..fast forward to 11:30 mins if you wish;



So the plaster cast in the photo might have also gone onto be used to make the pressing dies.

Pantographs not only allow the scale to be changed (obviously though they would have used 1:1) but also allow mirror images to be made so possibly they just "3D traced" one side of the clay model so they got a completely symmetrical body. Nice shot of the Continental star!

Unfortunately the real precision work of hand finishing the machine milled die surface isn't covered by the film. Unsung master craftsmen I'm sure.

However I came across the entire process in this film by Fisher Bodies in 1955 ...and its a lot more complicated, detailed and specialized than I think any car owner would imagine. No wonder a short run car like ours cost Continental so much per unit;



You might want to skip the first 5 minutes ...clearly the Marketing Department were on a little excursion to fantasy land.

[Barry Wolk]

What happened to the "Like" button? I really like this thread.

I think we should all encourage this type of post.

From the writer's perspective it'd be great if more people joined the conversation.

In fact, I didn't know that the dies were rough cast. I thought they were carved from forged steel carved to shape like they use CNC to carve styrofoam today. Does that mean the dies are hollow?

[Mark Norris]

Correct, they are indeed hollow but with a supporting "egg crate" structure cast in. You can see it at 13:15mins in the last movie and also in a modern die below;

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..and wandering a bit off topic, by contrast whole process appears a lot more straightforward, cheaper and quicker for fiberglass bodied production cars where a solid wood car body, or buck, was first made then molds taken from it. Here's the first Corvette taking shape about the same time our Continentals would be going through the conversion process from full size clay to steel dies.

mahogany_corvette_die1.jpg mahogany_corvette_die2_fullsize.jpg mahogany_corvette_die3.jpg mahogany_corvette_die4.jpg mahogany_corvette_die5.jpg

At least they only needed to make one side of the mold whereas steel bodied cars had to have a male and female die made for every panel.

So as Barry mentioned, using a plaster mold it was fairly easy to mock up the Mkii clay body design in fiberglass and drive it around on a chassis to see if you really like the look when it moves before committing to the expensive, no going back, steel die manufacturing process.

[Barry Wolk]

Elmer Rohn, in charge of HVAC and the interior of the Mark II was working on the seats of that Corvette when he was hired away from GM by William Clay Ford, personally. I have a packet of drawings from that project.