Make: 3D Printing (2014)
Part VIII. Other Ways to Make 3D Objects
Chapter 20. Milling 3D Objects
The takeaway on subtractive vs. additive fabrication.
Tom Owad
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 3DP
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 is. 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.
DIY CNC
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 your local hackerspace, TechShop, Fab Lab and even the MAKE forums or the Home Shop Machinist, 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.)
RESOURCES TO BUILD YOUR OWN CNC MILL
Build Your Own CNC Machine, by James Floyd Kelly and Patrick Hood-Daniel
http://amzn.com/1430224894
DumpsterCNC
http://www.dumpstercnc.com/
Build Your CNC
http://buildyourcnc.com/
Plans Avaliable from Buildyourcnc.com
To get the CAD and CAM files for the parts, go to http://buildyourcnc.com/cnckit2.aspx and 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 new option is the MakerSlide system, 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.
Tom Owad is a Macintosh consultant in York, PA, and Editor of Applefritter. He is the author of Apple I Replica Creation.
Even More Mills
This chapter was originally published in Make: Ultimate Guide to 3D Printing (2012). Since then there have been several new desktop CNCs and DIY linear motion systems released at a low price point.
It should also be noted that there are many different types of subtractive manufacturing in addition to milling, including laser cutters, vinyl cutters, and various CNC drag knife attachments.
Othermill
http://otherfab.com
The Othermill is a small-scale, high-precision CNC mill from Otherfab that evolved from the MTM Snap project (Machines That Make) created by Jonathan Ward at the MIT Center of Bits and Atoms. Jonathan now works for Otherfab.
This machine has a working area of 5.5"x4.5"x1.4” and is optimized for milling circuit boards out of FR-1 copper-clad PCB stock using a quiet, high-speed spindle. It can also machine soft woods, machinable wax, plastics and nonferrous metals. Unlike CNCs made from plywood, MDF, and other materials that are prone to warping, the Othermill is made from chemical resistant and moisture-proof HDPE.
In addition, the team at Othermill has taken on the task of both simplifying and beautifying the CAM process for milling by creating their own custom CAM package for the Othermill, which at the time of this writing is still in development. The cost of the Othermill will be a little over $1,000 for a fully assembled and ready-to-use machine.
Shapeoko 2
§ Documentation: http://www.shapeoko.com
§ Available though Inventables: https://www.inventables.com/technologies/desktop-cnc-mill-kits-shapeoko
Shapeoko is an open source CNC milling machine kit designed by Edward Ford that can be built in a weekend, depending on your level of expertise. It is available from Inventables as a Mechanical Kit ($299) or a Full Kit ($649 for 110V / $685.00 for 220V).
The Shapeoko lives up to its open source billing and provides full documentation for all of the machine parts, including the CAD files. It also uses the MakerSlide system discussed earlier in this chapter. The machine is driven by an open source hardware stack and currently uses grbl as the G-code interpreter and G-code sender (Windows) or gctrl on Mac and Linux. Materials for milling include plastics, woods, and nonferrous metals like aluminum and brass. However, it should be noted that Shapeoko strongly recommends a spindle upgrade (instead of using a rotary tool) if you plan to machine metals.
Linear Motion Systems
In addition to the complete and kit CNC milling options already mentioned, there are several companies providing open source aluminum extrusion combined with linear motion systems which make it easy to build your own custom CNC; MakerSlide, OpenBeam and OpenBuilds.
MakerSlide
§ Documentation: http://www.makerslide.com
§ Available though Inventables: https://www.inventables.com/technologies/makerslide
MakerSlide was created by Bart Dring and implements the traditional V wheel running on a V rail system of linear motion commonly used in commercial CNC machines. It was the first popular, affordable, and open source system of it’s kind and is sold through Inventables.com. The Shapeoeko 2 uses MakerSlide.
OpenBeam
§ Documentation: http://blog.openbeamusa.com
§ Avaliable through Amazon: http://store.openbeamusa.com
OpenBeam open source aluminum extrusions are used in the Mini Kossel and Kossel Pro 3D printers, which are both open source RepRap printers, as well as commercial (RepStrap) 3D printers that have emerged from a partnership between the Rostock and Mini Kossel creator Johann Rocholl and Terence Tam of OpenBeam.
OpenBuilds
§ Documentation: http://www.openbuilds.com
§ Avaliable through OpenBuilds Part Store: http://openbuildspartstore.com
The OpenBuilds Part Store sells OpenRail open source aluminum V-slot extrusions and other linear motion components. OpenBuilds V-slots are used in the Bukito 3D printer from Deezmaker.
Anna Kaziunas France