NEW YORK (TheStreet) Try as they might, my buddies Nick Pinkston and Danielle Applestone can't seem to make much of anything out of 3-D printers.

"3-D printing is limited by technology. The process is slow and expensive, and the materials are limited and expensive," wrote Pinkston, founder of Plethora, a San Francisco experimental rapid fabrication company, in one of what had to be 50 emails we've exchanged.

And Applestone, president of Other Machine, a similarly uber-cool 'Frisco-based emerging manufacturing operation, was equally unimpressed by 3-D printer tools from outfits such as 3D Systems, Stratasys, ExOne or Voxeljet.

"3-D printing is not even on our horizon," she told me on the phone last week. "The technology simply does not scale for manufacturing."

What's meaningful for investors, considering the recent swoon in valuation for 3-D printer stocks, is that Pinkston and Applestone absolutely, positively should be 3-D printer evangelists.

Both are deeply entwined in the emerging world of redefining how real things will really get made as these United States begin to relearn manufacturing. Pinkston's Plethora, for example, develops what amounts to an automated, on-demand manufacturing engine, similar in many ways to how software operating systems work. And Applestone's Other Machine is creating a line of personal manufacturing tools, similar to hip 3-D printers such as MakerBot. But her device mills, carves, etches or otherwise cuts things.

So, at least in theory, 3-D printers should be the perfect low-cost, easy-to-use manufacturing option for both CEOs. But no matter how much squinting, staring, prodding and hopeful thinking they could muster, neither can find a place for the type of additive manufacturing 3-D printing represents.

"Three-D printers are good for prototypes and complex shapes," said Applestone, who, by the by, has a Ph.D. in material science from the University of Texas at Austin and holds patents for lithium ion battery design. "But the parts don't last long and you get no sense for the mechanical properties of the item you are making."

Pinkston hit the nail the 3-D head: "The tools limit your thinking."

Not "makers" but manufacturers
Now comes the sad reality that should send 3-D printer investors to the valuation showers. It turns out these emerging manufacturing stars could not be more old-school in how they actually make their products. "Currently, we work with a very traditional, widespread technology called CNC machining that produces very accurate parts from a wide variety of metals and plastics," Pinkston said.

Applestone says her firm uses similar tools, in this case units from Oxnard, Calif.-based Haas Automation called a table router and vertical machining center. These two throw-back units help design and mass-produce her line of tabletop manufacturing mills. "At the end of the day, it boils down to a super accurate and fast way to cut sheets and blocks of stuff," Applestone said. "Nothing more."

And while not dirt cheap, these types of manufacturing options are so common and well understood that costs are insignificant when compared with high-quality, industrial-grade 3-D printers.

Applestone, for example, estimates that the all-in investment for her two mills is well south of $250,000. "And that is for a plant that can mass-produce real products fast and cheap," she said. "That's about the same price as a fancy 3-D printer, which can only make prototypes or, at best, limited numbers of products."

And that is not just top-line capital investment. The per-unit production costs for 3-D printing make almost no sense in modern manufacturing.

"A 3-D printer has poor amortization because the numbers of parts it produces per hour is far lower, and the cost of the special materials needed are far higher," Pinkston said.

He says these traditional techniques can make, say, a plastic spoon at a rate of 6,000 per hour on a $100,000 machine, from plastic that runs a penny per spoon. By contrast, the best 3-D printers today produce maybe 50 spoons per hour on a machine worth $500,000 and using plastic that costs a dollar per spoon.

"It should also be said that the spoons coming from the 3-D printer will be of such low quality that they would be unsellable in the market," he said.

Stop making 3-D sense
Now the true inner nuttiness of the 3-D printing prints up in crystal-clear detail. "Many say that in 3-D printing, you get complexity for free -- meaning that you don't have many constraints on what you can design," Pinkston said. "The caveat is that few people beyond artists have figured out good uses for this design freedom."

Both of these experts are flummoxed at how 3-D printing has gotten as established as it has. "I have no idea how 3-D printers got the credibility they got," Applestone said. "It's almost like listening to competing religious leaders. People are in different camps, making claims about what these things do that are simply not true."

"If we want manufacturing to come back," she said. "People cannot be thinking that, in any way, shape or form, 3-D printing is the only way to make something. It is just not true.

"We have got to get better information out there."

This commentary comes from an independent investor or market observer as part of TheStreet guest contributor program. The views expressed are those of the author and do not necessarily represent the views of TheStreet or its management.