There’s a lot of well-deserved excitement surrounding 3D printers, and for the avid DIYer much of it is focused on their ability to “self-replicate” by making their own parts. But is a 3D printer the right tool for you?
A 3D printer’s fabrication technique is additive — most of them use a hot plastic extruder to “print” a plastic model. This contrasts with subtractive fabrication tools, which start with a solid block of material and use a cutter to remove the excess. Subtractive fabrication is far more common than additive, especially when working with metal and wood. Lathes, mills, saws, drills, and other CNCs like laser and vinyl cutters are all subtractive tools.
The Subtractive Equivalent of 3D Printing
A CNC milling machine or router is the subtractive equivalent of the 3D printer. For the hobbyist, milling is inferior to printing in numerous ways.
Milling inherently causes waste, and without some sort of dust control, that waste gets flung throughout the room.
Milling is more dangerous — while it’s possible that a plastic extruder might overheat and catch fire, I’ve already had a (minor) fire with my CNC router, and there’s the added danger of a blade spinning at 20,000 rpm sending bits of itself, or even your workpiece, flying at you.
A mill or router is necessarily larger and heavier than a 3D printer and consequently more expensive and more difficult to move. It requires a positioning system that can maintain accuracy when encountering resistance, and motors powerful enough to drive it.
Software preparation is also more complex for milling. After drawing the object you wish to make in a CAD or 3D modeling program, it’s necessary to generate toolpaths with computer-aided manufacturing (CAM) software. This involves specifying the dimensions and location of the stock material, the dimensions and characteristics of the end mill (cutter), and speeds for the axes and spindle. The tools to do this tend to be complex, and a bit daunting for the first-time user.
From the user’s perspective, CNC milling is a much more complex process than printing. CNC milling does, however, have a significant advantage over 3D printing: the technology is mature. Home 3D printers are improving at a tremendous rate, but there’s often still a lot of tinkering and experimentation involved in getting a good print.
What Do You Want to Make?
If your interests tend toward larger and more structural creations, go with milling. Also consider that it’s cheaper to work in wood than in plastic, and that you’re likely to get substantially superior results.
On the other hand, making complex 3D objects is a lot more complicated with CNC milling than with a 3D printer. There are free tools for doing 2.5D milling, but CAM software for 3D milling can be very expensive and difficult to use.
Doing 3D work for 3D printing is much easier. You can design your models in a free program like SketchUp or Inventor Fusion, and then export an STL file. Slicing software converts the STL file automatically to toolpaths in G-code, then sends the G-code directly to your 3D printer. With 3D printing, there’s no need to tweak cutting paths, and no worry about the tool crashing into your work.
If creating small 3D objects is your goal, a 3D printer is the right choice.
Going with milling doesn’t mean you have to give up on self-replication or on making your own machine. Patrick Hood-Daniel, author of Build Your Own CNC Machine, makes a scratch-build CNC kit capable of making all of its custom parts, just like the RepRap 3D printer and its progeny. The frame is built of custom-cut plywood. Everything else is standard hardware.
The aluminum angle, bolts, and screws are available from any hardware store. The leadscrews and anti-backlash nuts will probably have to be mail-ordered from McMaster-Carr and DumpsterCNC, but you can get by with lesser hardware store parts in a pinch. The stepper motors and stepper drivers are completely generic and available from countless sources. The spindle is an ordinary wood router. I use a Porter-Cable 892.
As with the RepRap, the trick with Patrick’s CNC router is getting a seed unit. Fortunately, any CNC router that can handle a 2’×4′ sheet of plywood is capable of making the parts. Check out MAKE’s digital fabrication resource page for where to get CNC access, and you’re likely to find somebody local with the necessary equipment. (If you can’t find anybody to cut the parts for you, Patrick sells several kits.)
To get the CAD and CAM files for the parts, download the plans for the CNC Routing Machine Kit Version 1.3. Videos on the website explain how to put everything together. The files are licensed under the Creative Commons Attribution-NonCommercial license, which means you can make machines for yourself and for your friends, but you can’t sell them commercially.
The CAM files are in the proprietary CamBam format, but there’s a free version available, and it can read and write DXF files. Most good CAM software is very expensive, so if you don’t already have a favorite, stick with CamBam. It can do both CAD and CAM, and even the free version is tremendously full-featured.
Another exciting option is the open source linear bearing MakerSlide system by Bart Dring, available from Inventables. Perhaps the most significant weakness in the BuildYourCNC design is its decreased rigidity and precision due to its wooden design. MakerSlide integrates V-rails into what is otherwise a standard aluminum extrusion system (available from 80/20, Misumi, and others). By building your machine out of a combination of MakerSlides and stock aluminum extrusion, it’s possible to create a more rigid, precise machine than you could with wood.
This article originally appeared in both the 2013 Ultimate Guide to 3D Printing and the Make: 3D Printing book.