Who Invented 3D Printing? The Story Behind Every .stl File

Download a Tung Tung Tung Sahur model, and there is a good chance it arrives as an .stl file. Those three letters stand for stereolithography, a word almost nobody says on purpose. Chuck Hull defined it in a 1984 patent. Two years later he co-founded 3D Systems, 3DS for short, and it built the first 3D printer made for sale.

A lamp engineer and a cup

Hull’s day job was ultraviolet light. The National Inventors Hall of Fame says he was “developing lamps for UV-curable resins” when the idea for 3D printing came to him. Those resins are liquids that turn solid under UV light.

His idea: harden the resin one thin layer at a time, and stack the layers into a solid object. In 1983 it worked. The first part Hull printed was an eyewash cup, according to 3D Systems.

The real science

UV-curable resin is a mix of small molecules and a photoinitiator, a chemical that reacts to light. When light hits the photoinitiator, it forms free radicals. Those radicals link the small molecules, called monomers and oligomers, into a solid network, as Wikipedia explains. The resin turns to plastic where the light lands and stays liquid everywhere else.

The first commercial machine did this with a laser. A UV laser, steered by scanning mirrors, traced each layer inside a vat of liquid resin. A movable platform held the part, and the object grew from the bottom up, one slice at a time. When the print finished, the leftover liquid drained away. That is how the American Society of Mechanical Engineers describes it. If you own a resin printer, the vat will look familiar.

The patent

Hull filed his patent on August 8, 1984. The U.S. granted it on March 11, 1986, as Patent 4,575,330. It defines the word this way: stereolithography is “a method and apparatus for making solid objects by successively printing thin layers of a curable material, e.g., a UV curable material, one on top of the other.”

Hull did not expect what came next. “I didn’t think back then that I was spawning an industry,” he says in a quote on his Hall of Fame page. “I was trying to solve a particular problem.”

Was Hull first?

He had company. In 1980, Hideo Kodama of the Nagoya Municipal Industrial Research Institute in Japan filed what ASME calls the first patent application for rapid prototyping. He had already made 3D plastic parts by hardening polymer with UV light, and he published his method in Review of Scientific Instruments in 1981.

In France, Jean-Claude André, Alain Le Méhauté, and Olivier de Witte filed a patent for a laser device that builds models from liquid monomer. They filed on July 16, 1984, 23 days before Hull.

Hull took the next step. In 1986 he co-founded 3D Systems to bring the technology to market, and its SLA-1 arrived in 1987. ASME named the SLA-1 a landmark in 2016 and calls it “the first 3D printer manufactured for commercial sale and use.”

Where your .stl file came from

A printer needs a way to read shapes from design software. Hull developed the STL format to carry that data, and 3D Systems first documented it in 1988 in the StereoLithography Interface Specification, according to the Library of Congress.

An STL file describes the surface of an object as a mesh of triangles. It carries no color and no texture. Tung Tung Tung Sahur’s bat is just triangles until you pick a filament.

The format also goes by “Standard Triangle Language” and “Standard Tessellation Language.” Either way, the word underneath is Hull’s.

How 3DS collected the family tree

3D Systems (DDD on the New York Stock Exchange, and no relation to the Nintendo handheld) went on to buy two more branches of the family.

Laser sintering. Carl Deckard developed selective laser sintering as a graduate student at the University of Texas. A laser fuses powder, layer by layer, into a solid part. He filed his patent in 1986, received it in 1989, and co-founded a company called DTM to sell the machines. 3D Systems bought DTM in 2001 in a $45 million deal, TCT Magazine reports. The U.S. Justice Department required the two companies to license their patents to a competitor, because the deal would have cut the number of U.S. competitors in the market from three to two.

The name “3D printing.” At MIT, Emanuel Sachs, Michael Cima, and two colleagues received a 1993 patent for “three-dimensional printing techniques.” An inkjet head drops liquid binder onto a bed of powder, one layer at a time. MIT News calls it one of the first practical 3D printers, “and the first to be called by that name.” Sachs picked the name because of his father, a publisher: “Growing up, my father would take me to the printing presses where his books were made, which influenced my decision to name the process 3-D printing,” he told MIT News.

Z Corp was one of the companies that licensed MIT’s patent, and it added color printing. In January 2012, 3D Systems finished buying Z Corp, along with Vidar Systems, for $135.5 million.

So the company that sold the first 3D printer ended up owning a company built on the patent that named 3D printing.

The one 3DS couldn’t buy

If your printer feeds a spool of plastic through a hot nozzle, it comes from a different family. S. Scott Crump filed his patent on October 30, 1989. It covers “dispensing a material at a controlled rate from a dispensing head” in layers that “solidify and adhere.” The patent went to Stratasys, which built the first fused deposition modeling machine in 1991, according to ASME.

The patent expired on October 30, 2009. After that, anyone could build this kind of printer without paying Stratasys, and a large industry of filament printers grew, according to Wikipedia. Stratasys still owns the trademark on “FDM,” so members of the open-source RepRap project coined a name anyone could use: fused filament fabrication, or FFF.

3D Systems did try. In 2023 it offered to buy Stratasys. In September, Stratasys’s board ended the talks.

If that is your printer, the machine descends from Crump. The .stl you feed it descends from Hull.

Print the idea

Every printer in this story builds the way Hull’s patent put it: thin layers, “one on top of the other.” You can watch it happen. Open your slicer, load any model, and drag the layer preview slider from the bottom to the top. That is the whole invention, one slice at a time, and it beats another lap of the feed.

Hull’s first print was a cup. Yours can be a creature.

Find your next print in the field guide. Every specimen links to free 3D prints.

Sources

• Charles W. Hull, “Apparatus for production of three-dimensional objects by stereolithography”, U.S. Patent 4,575,330, filed August 8, 1984, granted March 11, 1986.
• National Inventors Hall of Fame, “Charles Hull”.
• 3D Systems, “3D Systems’ Co-founder & Chief Technology Officer, Chuck Hull, Awarded National Medal of Technology and Innovation”, October 2023.
• American Society of Mechanical Engineers, “Stereolithography: The First 3D Printing Technology”, landmark brochure, 2016.
• Wikipedia, “Photopolymer”.
• Hideo Kodama, “Automatic method for fabricating a three-dimensional plastic model with photo-hardening polymer”, Review of Scientific Instruments 52, 1770, November 1981.
• Jean-Claude André, Alain Le Méhauté, and Olivier de Witte, “Device for producing a model of an industrial part”, French patent FR2567668, filed July 16, 1984.
• Library of Congress, “STL (STereoLithography) File Format Family”.
• Carl R. Deckard, “Method and apparatus for producing parts by selective sintering”, U.S. Patent 4,863,538, filed October 17, 1986, granted September 5, 1989.
• TCT Magazine, “‘A creative genius with so much more to contribute’: tributes paid to Selective Laser Sintering inventor Dr Carl Deckard”, January 6, 2020.
• U.S. Department of Justice, “Department of Justice requires 3D Systems Corporation and DTM Corporation to lift patent entry barriers”, August 16, 2001.
• Emanuel M. Sachs, John S. Haggerty, Michael J. Cima, and Paul A. Williams, “Three-dimensional printing techniques”, U.S. Patent 5,204,055, granted April 20, 1993.
• MIT News, “Printing off the paper”, September 14, 2011.
• MIT News, “A new era in 3-D printing”, May 16, 2019.
• 3D Systems, “3D Systems Completes the Acquisition of Z Corp and Vidar”, January 3, 2012, filed with the SEC.
• S. Scott Crump, “Apparatus and method for creating three-dimensional objects”, U.S. Patent 5,121,329, filed October 30, 1989, granted June 9, 1992.
• Wikipedia, “Fused filament fabrication”.
• SME, “Stratasys Terminates Discussions with 3D Systems”, September 12, 2023.