Chris Reilly

The purpose of this research is to create freely distributed designs for CNC devices such as multi-axis mills or 3D printers, which can be built for relatively low cost (under $500) from commonly available hardware.  Designs will include parts lists, detailed assembly instructions, and tutorials on construction, use and modification.

This research proposal is directly related to the Easy, Open-Source Toolpath Software proposal and the DIYLILCNC project, and could take place as concurrent or separate research.

Background

CNC devices such as waterjet cutters, laser cutters, CNC mills and 3D printers have had a large impact on industry and manufacturing over the last several decades.  The precision and repeatability with which a CNC device can fabricate a part are on par with more mature mass production techniques such as casting or die stamping; however, unlike traditional mass production processes, CNC manufacturing is not subject to the constraints of inflexibility and lead-time for machine setup.  Generally speaking, it is no more expensive per part to use a CNC device to fabricate a single iteration than it is to produce multiples, unlike mass production where one-off products are prohibitively expensive due to setup costs.  CNC-fabricated parts are based on descriptions stored in digital files, allowing for relatively quick and easy modification, as well as sharing over long distances.

For all their benefits, CNC devices are still marginal tools from the perspective of a small-scale artist, designer or tinkerer (aka Maker).  This is due in large part to the high cost of such devices.  Even a low-powered, relatively small laser cutter can cost upwards of $10,000, and prices for other CNC devices only increase from that point.  Service bureaus such as Shapeways or Ponoko offer a degree of access to CNC processes, however the expense and long turnaround time of these services negate one of the most obvious benefits of access to CNC devices: quick, cheap prototyping.  Further, the software used to create and prepare a CNC part description can be both prohibitively expensive and difficult to use; most of the educational content centered around CNC manufacturing and software processes is aimed at engineers and machinists, and is often unhelpful to Makers with more diverse backgrounds.

CNC manufacturing is in a state today that parallels digital computing in its early stages: devices are expensive and scarce, making access on the part of the untrained masses difficult, if not impossible.  Just as Computer Science students and programmers once rented time on large mainframes so that a technician could process their painstakingly organized punch card programs, so today do Makers pay technicians to process their tediously formatted digital designs into CNC manufactured parts, often at prices ranging into hundreds of dollars per hour.  Fortunately, digital computing has undergone its own revolution in the past several decades, leaving Makers with ready access to cheap, small, powerful computers that are easily hacked to process and distribute information as their users see fit.  The digital computing revolution comes at the tail end of a centuries-long shift in information control.  Images and text were once produced by just a handful of elite individuals; since the advent of the mechanical printing press, there has been a steady push towards democratizing hardware technology that enables ordinary people to create and distribute information.

In order for digital fabrication technology to show its true potential, CNC devices must undergo a change similar to that of digital computing and information production.  Since the Industrial Revolution, production of physical parts and products has been controlled by a relatively small number of industrialists.  Networks of distributed, low-cost CNC production devices have the same democratizing potential for the means of physical production as digital computing has for information production: putting creative control in the hands of non-experts.  The implications of such a change are potentially huge; many basic scenarios that we take for granted, from the size and orientation of our cities to the way we grow and eat food, are byproducts of mass production’s role in society.  The proliferation of easily accessible designs and supplementary educational materials that facilitate construction and modification of these devices is the first step towards a distributed object creation network.  Further, the technical fundamentals learned from constructing one type of CNC device “from scratch” transfer easily to other applications of CNC control; a user who builds a CNC mill, for example, will have an easier time constructing a 3D printer, etc.

Technical Challenges

CNC fabrication depends in large part on mechanical precision in the moving parts of a device.  The majority of manufactured precision bearing hardware is quite expensive, as it is built to work within very small tolerances of error.  For many applications of CNC fabrication, high levels of precision and accuracy are very important; for other applications, wider margins of error can still yield perfectly useful results.  This research aims to find a happy medium between cost and precision, sourcing parts that are cheap, yet form assemblies that maintain a “pretty good” level of precision.

CNC devices also require a level of rigidity to their mechanical structures, especially those devices which become physically engaged with material during the fabrication process.  CNC mills, for example, engage a cutting tool with a piece of stock material, and so must be rigid enough to overcome the resistance of the stock during cutting; laser cutters, on the other hand, do not come into direct contact with stock, and therefore are not as constrained by mechanical strength.  The problems associated with rigidity are overcome in most high-end CNC devices by constructing mechanical frameworks out of strong, rigid material such as steel or aluminum.  This approach solves the problem of rigidity, but creates additional design issues: the high cost of such materials increases the cost of constructing the device; the extra weight of rigid materials must be matched with more powerful motors and electronics to drive them, further adding to the cost; and finally, such materials are usually more difficult to work with, making future modifications to a device less likely to take place.  This project will focus on construction materials that are relatively cheap and easy to work with, yet still maintain a workable level of rigidity and durability, through a combination of joinery design and careful material sourcing.

Issues of mechanical rigidity and precision in CNC device design are ultimately dependent on the availability of standard hardware and stock materials.  Building materials that are widely available ensure that the maximum number of potential Makers will undertake a build.  A common problem in distributed, Maker-constructed CNC devices is the availability of metric vs. imperial hardware; outside the U.S., metric hardware is the standard, however most designs originating in the U.S. favor imperial.  Further, over-engineering a CNC device can lead to a bloated bill of materials, adding expense and unnecessary complexity to the build process.  In order to facilitate the distributed construction of CNC designs, this research will focus on sourcing parts that are widely available, and used efficiently to facilitate construction with the fewest number of parts possible.

When commonly available hardware and stock are not sufficient to address a mechanical engineering challenge, custom parts must be fabricated; this can be accomplished through a range of techniques.  Cutting complex custom parts on other CNC devices is a great option, since digital files with accurate and precise descriptions of parts can be easily shared among Makers.  While it is theoretically possible to use CNC devices to fabricate every single part of a machine design, the cost would probably be prohibitively high for reasons mentioned above.  Not every part of a CNC device warrants CNC fabrication; rectangular parts, for example, are perfect candidates for table saw fabrication, and linear dimensions are easily communicated.  This research will focus on creating designs that use a combination of CNC fabrication for complex parts and traditional shop fabrication for simpler parts.

The designs created under this research project are made with the goal of accessibility and understandability on the part of a Maker with basic shop & electronics skills.  The elegance and effectiveness of any design intended for execution by Makers falls flat unless that information can be effectively conveyed in an easy-to-follow format.  Additionally, as Makers suggest changes and improvements to build instructions, designs, and reference materials, it is important to consider the format of design instructions so as to allow for relatively easy modifications.  For example, a wiki-style web repository of build instructions is more suitable to this end than a printed document or book.

Sketches & Prototypes