[LDFF]

Hi guys.
Well this thread is a cry for a history lesson. My questions are concerned with the technology that existed in the beginning of the XX century, specifically how were metal stamping dies (you know, to make car doors/hoods/fenders) made?

Back then there were no computers, no CAD/CAM programs to help us, so how did they carve the molds of the fenders of, say, Ford Model A?
I can imagine them using tools to machine said dies by hand, but how did they make sure the dies were up to the designer specs? With careful machining? And how, after machining a die for the left fender, did they make sure they created the die for the right fender as a perfect symmetrical? Was there any jig? Was it once again done by somebody with steady hands and a remarkable attention to detail?

If you guys have some information or you know the title of old books on the subject, even some old photos will make me thank you a lot. I find this type of history extremely fascinating.

[Al_The_Man]

Tool & Die makers made them by hand.
I have seen proto type car panels such as fenders, hoods, etc, panel beaten by hand to produce the prototype model, when the car was finished you could not tell the difference in that and the eventual production model.
I was at the MG factory when the MGA came out.
Many of the Tool & Die apprentices were 'poached' by US companies on the completion of their apprenticeship.
Al.

[packrat]

Plaster master forms and a Keller tracer mill were still being used when I started the trade in 1966. After the tracer was done you used angle grinders, then files and then sand paper and stones to finish. All of the last steps done to contour gauges made for the die you were working on. Even had a tracer for the Bridgeport and lathe.

Most of the fender dies were made of either cast iron or for real short runs Kirksite. When working on the cast iron dies, the bottom of the bath tub would be a rusty brown color after a bath. Don't even miss those "good old days".

As far as the fenders being the same from side to side, never happened. Even two fenders of the same side, from different dies weren't the same, when actually measured.

[Dylwad]

Totally agree about the fenders never being the same, did heavy collision for years and many times had to explain to customers that the opposite side of the wreck always looked that bad, they just notice the bad gaps and fit now that they were looking for it.

Also built many show quality cars and it takes an enormous amount of bodywork to get a "perfect" car straight and clean.

As for pre-cnc, our current smart phones have thousands or millions of times more computing power than what was used to get us to the moon, but only a tiny fraction of what the human brain is capable of.
CAD software is based on age old equations born in the time of compasses and slide rules, trigonometry has been understood for ages. Draftsmen and machinists used to be very good at math because they needed to be.

If you needed a complex shape you worked it by hand and used a manual machine to copy it into a die or form for mass production.

The B-29 project was bigger and more complicated/expensive than the atomic bomb project, probably partly due to what it took to figure out mass production, all done before cnc.

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[RICHARD ZASTROW]

Pantogrph type machines as the Kellering machines that packrat mentioned. The finished dies were as accurate as the models that were produced by hand. Thanks to SKILLED tool and die men.

More often than not, the variances between parts was in the way the fenders, doors etc. were located in the die/press system.

The same type of skills produced some pretty nice equipment like Norton bombsites etc.

Dick Z

[LDFF]

Hi guys, sorry for the late reply but I was getting a report saying this was not a safe website.

I have to say that english is not my first language and that I am not into the industry (yet). So I made some images to try and get a better view of the process back then. Let's say I want to build this fender:

Attachment 191680

Please don't mind the design (or lack of). It's just to understand the process.
Back then some bodywork expert would pound a metal sheet and use an english wheel to produce the piece to my design standards, am I right? Then he, or someone else, would create the negative of said fender in plaster:

Attachment 191682

But because this plaster material can't really support the stress it would be subjected to in a stamping process, we need to create an exact copy in a harder, stronger material (like steel). Hence the pantograph milling machine that would create said copy in steel:

Attachment 191684

Is this the process of producing a die back then when CNC didn't exist? Did I get it right? Is there any book or paper that I can use as a reference if I want to write an article about this process?

[packrat]

The usual way was to start with a full size clay model of the car that was being designed. This way it could be viewed from all directions, and the clay could be resculped if it didn't look correct.

Then a plaster negative was made from the model. Then a positive from the negative. The positive had a wooden frame work in it to make it lighter and use less plaster. The plaster positive was then coated with varnish to make the surface harder.

The positive was then used in the Keller mill. And then the metal (most times cast iron not steel) die was used to make the parts.

You show a drawing of the whole fender shape being made at one time. This is rarely done, usually done in steps. This is due to the presses not having enough stroke. And the sheet metal not being able to move that much in one step, without tearing.

Even though they call making car bodies "stamping", it is more of a "drawing" process.

Sounds like your a student, does your school belong to Wiley Online? lot of stuff there, just one link; Stamping and Metal Forming Processes - The Automotive Body Manufacturing Systems and Processes - Omar - Wiley Online LibraryOr try here; https://www.google.com/search?q=The+...ient=firefox-a

[LDFF]

packrat thanks for your replies I really like to get all this insight. And yes I am a student. I have already completed a couple of classes about modern manufacturing processes, so I know about the limits of formability and about deep drawing LDR. Yes a fender would rarely be formed in a single shot, but I am not really concerned about the manufacturing process in itself, I am just concerned about the die creation. Even so I don't really want to be pedantic, it's just that I am really interested in how were things made before computers.

But back to your last reply you said they used the positive to make the dies. Why the positive and not the negative? And how did they apply pressure to the metal sheet to make it conform to the die? With hydraulic pressure? Or with a negative?
And a final question, why did they use cast iron for the dies? Isn't cast iron usually more brittle than steel?

[packrat]

Cast iron is just like steel or aluminum, available in many different flavors. It is easier to machine and cheaper. A piece of tool steel the size of a fender, would cost many times the price of the same size cast iron. And until the "trim" stage is met, there no real need for a hardened steel tool.

There are a couple of different ways that the presses worked. In the old days it was pretty much mechanical. With one or more "cranks" in them, depending on what the tool needed. Each crank had a different offset, so the movement went to different depths of draw. Then they went to hydraulic or hydraulic mechanical combination presses.

The parts/fender would be, depending on the shape, either done with the positive and negative dies coming together. Or they would first be "stretch formed" over a positive and then the finished by the positive/negative method. But one thing they all had in common was a form of hold down plate or stripper plate. This held the metal sheet captive. But it also allowed it to move at a certain amount of pressure. This allowed the stretch forming and helped to keep wrinkles from forming in the part while it was being formed. A third thing is that it knocked the part out of the die after forming.

The positive master was used because of the way the Keller mill worked. From the positive master, both positive and the negative parts of the die could be made. By the way the Keller was used, to move the spindle.

Sorry I didn't answer your questions in the order asked.

[uli12us]

Another reason is, you can cast your rawpiece near to the endshape of the die. That will save tons of material not only to buy as well to remove.