PERSONAL FAB

BY TOM OWAD

Building a CNC Mill

There’s a lot of well-deserved excitement surrounding the RepRap 3D printer, and much of it focuses on the RepRap’s ability to make its own parts. The RepRap’s fabrication technique is additive — it uses a plastic extruder to “print” a plastic model, one layer at a time.

This contrasts with subtractive fabrication techniques, 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, and drills are all subtractive tools. A CNC milling machine or router is the subtractive equivalent to the RepRap 3D printer.

For the hobbyist, milling is inferior to printing in numerous ways. The method inherently causes waste, and without any sort of dust control, that waste gets flung throughout the room.

Milling is more hazardous: 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 20,000rpm, sending bits of itself, or even your workpiece, flying at you.

A mill or router is necessarily larger, heavier, and Patrick Hood-Daniel’s Expandable CNC Kit consequently more expensive and more difficult ( buildyourcnc.com) is a CNC router capable of to move. It requires a positioning system that can making all of its custom parts. The router’s frame maintain accuracy when encountering resistance, is built of custom-cut MDF (medium density and motors powerful enough to drive it. fiberboard). Everything else is standard hardware.

Software preparation is also more complex for The aluminum angle, bolts, and screws are avail-milling. After drawing the object you wish to make able from any hardware store. in a CAD or 3D modeling program, it’s necessary The lead screws and anti-backlash nuts will to generate tool paths with CAM (computer-aided probably have to be mail-ordered from McMaster-manufacturing) software. This involves specifying Carr and dumpstercnc.com, but you can get by the dimensions and location of the stock material, with lesser hardware store parts in a pinch. The the dimensions and characteristics of the end stepper motors and stepper drivers are completely mill (cutter), and speeds for the axes and spindle. generic and available from countless sources. The

The tools to do all this tend to be complex and spindle is an ordinary wood router; I use a Porter-a bit daunting for the first-time user. From the Cable 892. user’s perspective, CNC milling is much more As with the RepRap, the trick with Hood-Daniel’s complex than printing. CNC router is getting a seed unit. Fortunately,

CNC milling does, however, have a significant any CNC router that can handle a 2'× 4' sheet of advantage over 3D printing: the technology is MDF is capable of making the parts. Start looking mature. The RepRap is improving at a tremendous around the forums at makezine.com or The Home

rate, but there’s still a lot of tinkering and experimentation involved in getting a good print. If 3D printing technology fascinates you, the RepRap is a great project to get involved in, but if your interest is in making things, CNC milling is the better option at this time.

Going with CNC milling, however, does not mean you have to give up on self-replication or on making your own machine.

CNC milling has a significant advantage over 3D printing: the technology is mature.

If 3D printing technology fascinates you, the RepRap is a great project to get involved in — but if you want to make things, CNC milling is the better option at this time.

40 Make: Volume 18