A plastic showpiece manufactured using 3-D printing on display at a convention in Erfurt, Germany, last week. © Martin Schutt, dpa, Corbis

We can see the future -- make that futures -- of 3-D printing from here, but which future will it be?

You may have seen the video or heard of the stunt in which a group called Defense Distributed fires a gun made with a secondhand 3-D printer. From software instructions, the printer built up the gun from layer after layer of plastic. That has set off a firestorm of protest from people worried about the security implications of a plastic gun that anyone with access to a 3-D printer and the software program, initially distributed on the Internet, can make and that doesn't set off metal scanners. Support comes from people who believe that anyone should have the ability to make a gun or who see this as a logical extension of the Second Amendment right to bear arms.

But I think the focus on the use of a 3-D printer to make a gun doesn't recognize the truly disruptive economics of 3-D printing technology.

Companies will be able to use 3-D printers to make parts for complex and finely tuned industrial products, such as jet engines, that now need to be cast and machined and welded. Not someday, but now. General Electric (GE) has started using 3-D printing to build fuel nozzles for jet engines. The process involves melting a bed of cobalt-chromium powder with lasers and then using 3-D printers to build up the nozzle, thin layer by thin layer, following software instructions. Traditional manufacturing requires welding 20 small pieces together.

You will be able to walk into a Staples (SPLS) store and use a 3-D printer to build a prototype of a chair or a model of a building out of thin layers of paper glued one on top of another and then cut to the right shape by the printer following software instructions. Not someday, but now. The first Staples store to offer the printer and software from private Mcor Technologies opened in the Netherlands in April.

You'll be able to buy a home printer and create your own one-off "Star Trek" collectibles -- not someday, but now -- using software and printers from 3D Systems (DDD).

You -- well, your dentist actually -- will be able to create models of your choppers using 3-D printers and software from Stratasys(SSYS). Not someday, but now.

image: Jim Jubak

Jim Jubak

Auto companies will be able to use a 3-D printer to prototype new engines and to produce components for high-pressure fuel injection systems using 3-D printers and software from ExOne (XONE) -- not someday, but now.

3 different approaches

But it's not at all clear which one of those approaches to the 3-D future will grab the biggest share of the 3-D future. Nor do we know which one will lead in building a significant market and which will lag.

And that's important to you as an investor because each of the three highest-visibility publicly traded 3-D printer companies is emphasizing a different approach to the future.

Here's my own survey of the landscape.

3D Systems: P/E 108.4. Market cap $4.86 billion. Q1 revenue $102 million, 31% growth. GAAP earnings of 6 cents a share. 3D does make higher-end printers for production, but I'd say the company is more heavily weighted toward the enthusiast and personal printer market than either Stratasys or ExOne. The company's Cube 3D sells for $1,299, and its ProJet 1000 comes in at $4,000. (I'd call MakerBot and its Replicator series the purest enthusiast play, but the company is still private.)

The enthusiast and personal market is certainly an attractive one; it's the part of the 3-D printer market most likely to build the volumes that make Hewlett-Packard's (HPQ) printer/ink strategy work so well. In 2011, $137 million of the 3-D company's $230 million in revenue came from the sale of printers and $93 million came from the sale of proprietary plastic and powders (the "ink" of the 3-D printer).

But the worry is that the personal market will be slow to develop. Very few individuals need to have a $1,299 3-D printer at home. The company's aggressive acquisition strategy, with 30 companies purchased since 2008, makes it hard to tell what the actual organic growth is in this end of the market. Recently, 3D Systems sold stock to raise $250 million. The assumption is that the company has another, comparatively larger, acquisition in mind.

No more plaster molds

Stratasys: P/E 158.8. Market cap $3.5 billion. Q1 revenue $98 million. 2013 projected revenue $430 to $445 million. 2013 projected GAAP loss of 16 cents to 41 cents a share. I'd say that Stratasys emphasizes the professional market, although the company certainly sells its Fortus line of production systems. That emphasis got more pronounced with the merger of Stratasys and Objet.

For example, one of the products being pushed after the merger is the Objet 3 OrthoDesk, a 3-D printer for the orthodontic market. An orthodontist will be able to create models of a patient's teeth and then, using the printer, turn those into the specific dental applications that the patient needs. No more plaster molds that have to be turned into casts and then made by hand into braces, bridges, replacement teeth and other dental aids. The physical molds won't have to be stored, either, so that they can be retrieved for future work for the same patient. Now the information contained in the physical mold can be stored digitally.

A joint venture between a 3-D printer company like Stratasys and a 2-D printer company like Hewlett-Packard would seem a natural. After all, the established 2-D printer company has the sales channels and customer support to push a product like the Objet 30 -- or Stratasys Idea line of personal printers -- into the marketplace. The two companies thought so, too, and they formed a partnership that would do exactly that.

But they dissolved that effort relatively quickly for reasons that, to me, seem unclear. Stratasys has said only that the effort didn't work and that the two companies agreed to part ways.

My suspicion -- and that's really all it is at this point is that the two companies discovered that the early stage of development in the 3-D printer market didn't fit together all that well with the mature 2-D printer market. No one needs to explain to a customer how a 2-D printer works or to spend time persuading a business to make the leap of putting a 2-D printer on a desktop. Yet that is exactly what the 3-D market demands at this point; the potential 3-D printer customer needs convincing and hand-holding and semi-customization of the product to business needs.

Hewlett-Packard's marketing apparatus is admirably suited to selling the mature 2-D printer, but selling 3-D printers would require significant retooling of that marketing force. The Hewlett-Packard association with a 3-D printer would work to persuade hesitant customers, but only if those customers had a satisfying rather than frustrating experience with the Hewlett-Packard sales and support teams.

Youth and immaturity

ExOne: Forward P/E 56.3. Market cap $561 million. Q1 revenue $7.9 million. GAAP loss 20 cents a share. ExOne is so newly public and so young as a company that it's dangerous to draw conclusions about the company's exact focus. (ExOne would probably not have been able to go public at such an early stage except that the stock market success of Stratasys, and especially 3D Systems, created investor demand for more opportunities to invest in 3-D technology.)

But with that caveat, I'd say that the capabilities and higher unit price of the company's printers indicate a focus on the industrial prototyping and production end of the market. The example that I cited earlier -- the use of a 3-D printer to prototype new automobile engines and to produce components for high-pressure fuel injection systems -- is indicative of the company's market direction at this point in its life.

The very youth and immaturity of ExOne helps focus the key question about investing in 3-D printer companies. Certainly, 3D Systems has become a momentum-investing favorite; the stock's 108 price-to-earnings ratio reflects that. But considering how speculative projections of growth rates are and how uncertain the economics are -- for example, how much money will these companies need to raise to build the sales force required to advance them from their current near R&D stage? -- it's hard to come up with a way to put a fundamental value on any of these companies or to pick one as having come up with the winning approach to the developing 3-D printer market.

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