A 3D Glue Gun Does Not Self-Replication Make

I’ve been wondering at this ever since the meme has been circulating. People make a printer that shoots glue, layer upon layer and thus it can print 3d objects.

But saying such 3d printers will replace factories and manufacturing is very clearly wrong. Take a look at almost anything you’re using or wearing right now. It’s a mishmash of materials gathered from various sources all around the world. Yet the 3d printers can only make single material objects, usually of some hardened glue. The rest has to be added later.

It’s as if saying that if you have an axe, a saw, a chisel and a knife that you will never need any manufactured products ever. And actually, you can make a lot with those and your own hands, or at least used to in the society of the past when people didn’t use such a vast array of objects. You can make a new shaft for the axe with the axe. But you definitely can’t make a blade. Modern metals use iron ore from one place, coal from another, additives from all over the world (nickel and chromium for example)… All excavated and refined with very sophisticated mechanical, chemical and even sometimes biological systems. And electronics are a million times harder than that. You need very high purity silicon and dopes, all kinds of fancy metals and polymers, assembled with very high accuracy in a clean room…

The difficulty of “bootstrapping”, starting a self-sufficient system from scratch (or using only nature’s services, a very big help not really available in space), is very very much underestimated.

And self-replication… Building a machine that can build itself is clearly not very far along the way if the printer can print a couple of rods that are then bolted together with metal screws (that it can not manufacture) to form the printer’s frame. A normal person would build the frame from wood (no infrastructure required to grow wood) much faster. And there’s the whole motor, injector and electronics issue. The frame is not the hard part about the replicator.

So the problem is a material, chemical and heat one. How can you build a machine that machines/transforms/builds parts that are made from a material that is as hard as the hardest material on the machine itself? Or how will it melt materials whose melting point is higher than what the machine itself can handle? What about solvents and chemical issues? How will it produce electronics from organic materials? Batteries? Magnets for motors and actuators? There are a huge amount of clever tricks that have to be done to make such stuff to work. For example, one could use two nozzles spraying different components, that pass an area right after each other, forming a glue that only hardens when the components come in touch with each other.

Also, clearly, biological ecosystems can be self-sustaining. Cells can perform extremely complex and impressive chemical functions. How can a bacterium cell take in food and build a copy of itself so easily?

I’d say trees (for wood), hemp and cotton (for fibers), leather and wool from animals and the million other things that enable hand manufacturing from minimally human-processed raw materials are much more easily available and also much more versatile, durable and sustainable materials than any 3D glue printer.

The 3D printer can be useful in manufacturing rarely repeated complex shapes where the accuracy of the shape is important. (Prototypes of complex manufactured goods often.) If the shape is not as complex or as important, it’s faster to make it by hand (an axe shaft). If many are desired, it’s easier to build a more capital expensive mold or other manufacturing process (stamping for example) for them.

The whole self-replication problem is a fascinating thought experiment nevertheless. For example, NASA has looked at it before, in a summer study, used for a moon base. It is a very important question if humanity ever wants to use resources beyond the planetary scale.

It even has analogies in computer science. When starting a new computer language, one generally has to build a compiler (A) for it at first in another language (one doesn’t want to write machine code directly). Then when one can compile (with A) a compiler written with the new language itself (B), and that resulted compiler executable can compile a compiler from the new language source code (C), you have reached self-sustenance. Ie when C can compile C. Even if all the other languages ceased to exist, one could keep on compiling machine code and adding new features to the language with the new one. Some people with more formal education in computer science can probably muse about this with much more insight.

And thanks to Kari Luojus for the link!

Edit: When I look at the electronics list at the RepRap homepage, I can just see how long a road there is to self-replication: Thermocouples, optical detectors, transistors, capacitors, magnets… All needing different chemical elements for their fundamental properties.

Biological systems go to very great lengths to sort and synthetize the needed compounds from the food on a molecular level to keep the organisms healthy, growing and reproducing. They (and we) need trace elements like some metals, as well as some hard-to-synthetize molecules like vitamins. The whole complex cycle of the biosphere provides them. The established science of nutrition has only existed for a few hundred years, since all this was thought to be so obvious, but is actually very complex when looked at more closely.

I don’t know how many different chemical materials are used in the simplest insect eyes, how many are derived straight from food and how many are synthetized. Even the photosensitive cell’s detector’s building block, a single protein called Rhodopsin is actually very complex and synthetized in multiple steps, one needing vitamin A.

A lot of substitutes can of course be used when lower efficiency is accepted, but there are so many orthogonal requirements that self-replication of reasonably advanced manufacturing machines will clearly need a big assortment of raw materials.

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2 Responses to A 3D Glue Gun Does Not Self-Replication Make

  1. Pingback: PRINTERESTING · Evolution of Print

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