3-D printers have exploded onto the scene, and publicly traded 3-D printing companies like Stratasys (NASDAQ:SSYS) and 3D Systems (NYSE:DDD) have seen their stock prices soar as the technology serves up rapid adoption rates that have outpaced expectations. But could a potential flood of self-printing printers threaten the leading desktop 3-D printers along with major 3-D printing companies' future gross margins?

The RepRap project
Anyone familiar with 3-D printing is also familiar with the RepRap project. What is the RepRap community project all about? It's an open-source 3-D printer revolution aimed at making self-replicating machines that are freely available for everyone.

Investors in the 3-D printing space take the RepRap project seriously. Though it's not a company, it is competition to publicly traded players -- particularly to consumer FDM 3-D printers like the Stratasys MakerBot and the 3D Systems Cube. In fact, a 2012 study by Moilanen and Vaden asserted that RepRap printers are the world's most widely used 3-D printers.

Should 3D Systems and Stratasys investors be worried about the development? Or, more specifically, could this open-source development grow to the point that it begins to drive consumer-printer prices down? That's a very real possibility -- and one of the factors that have kept Motley Fool industrials analyst Blake Bos from making any recent bullish calls on Stratasys.

Meet the Mini Metal Maker, the missing link to self-printing 3-D printers
The just-unveiled Mini Metal Maker is, in more ways than one, an illustration of how printers could print competition.

First, parts of the Mini Metal Maker were printed with the MakerBot. And there will be plenty of other creative makers printing new printers with the help of existing printers.

Second, since the Mini Metal Maker is able to print metal parts at home, it helps the RepRap print parts to duplicate itself that couldn't be printed at home before. In a recent interview with Mini Metal Maker David Hartkop, he explained how the Mini Metal Maker is another key step to self-printing printers.

Notably, Hartkop's Mini Metal Maker is still in the prototype stages. But it does illustrate the threat of new printers that could easily flood the marketplace with the help of existing printers. Sure, even if the Mini Metal Market came to market as a finished product, it wouldn't compete directly with Stratasys or 3D Systems -- it's simply too different from the MakerBot and the Cube. But it does illustrate the potential competition that could arise from printed printers.