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MakerBot's 3-D printers will soon be able to produce items that look like bronze, limestone, and wood, thanks to a new line of plastic-based composite materials shipping later this year. But the launch may be too little, too late: Entrepreneurs and artists interested in working with metal and wood are already embracing desktop milling machines that can handle the real deal.
The calculation is simple: Buy a MakerBot Replicator, the leading desktop 3-D printer, for $2,889, and you can produce plastic prototypes or the kind of trinkets that you might find in a Happy Meal. Buy a small-scale milling machine like the Othermill, which retails for $2,199, and you can make jewelry and mechanical parts out of everything from aluminum to walnut.
"Once you can cut metal, you can make things that last," says Danielle Applestone, chief executive of Other Machine Co. "For the first couple of months that I was working here, I was scared of cutting with metal. It was louder, I was worried I was going to break the tool. But as soon as I jumped in, it quickly became like wax to me."
"Metal is power, it really is," she says. "You don't go back."
It should be noted that MakerBot's base model also went from $400 to almost $3K when Stratasys acquired them.
Original Submission
(Score: 2, Informative) by scyther on Thursday June 11 2015, @04:04PM
If only a car was as simple as its driveshaft!
I'll grant that desktop CNC mills for wax and composite wood products are not too far-fetched -- Roland brings their newest model to Siggraph every year and they are indeed getting smaller. But machining even soft metals like aluminum is not trivial.
The cutting forces at play in a milling machine are substantial and managing them is costly. For instance, the helical blade of the milling cutter has a tendency to push and pull the material vertically as it cuts. So you need a fixture with a lot of mass to prevent the workpiece from moving as it's being milled. Once you get that under control, you'll notice that the machine itself will flex when you make a cut. So the machine has to be physically massive as well. If the machine, workpiece and cutting tool are permitted to vibrate you'll get lousy parts and you'll wear your cutter out more quickly.
(By the way, a 3/8" cutter for aluminum can run between $12 (McMaster 3051A15) and $35+ (8926A451) and has a lifespan measured in hours.)
A second and related problem is precision: when working with metal you need accuracy and repeatability on the order of thousandths of an inch / hundredths of a mm. If you cut a nice clean edge, then move the tool to work elsewhere on the piece, then move back to your edge, it's not acceptable for the tool to have gouged your clean edge, nor for the tool to be hovering .003" away from the edge. It needs to be exactly where it was before -- since machines have limited cutting power, deep pockets and other features have to be cut in steps or layers and you want them to be flush.
Belts are no good for driving these machines. They're good enough for 3d printers, but not rigid enough for metalworking! If you agree that the moving parts of a mill ought to be rigid and consequently massive, you can see that an elastic drive system is ill-suited. Your great grandfather's mill probably used an Acme screw - these work but are not ideal for hobby-grade CNC machines because the pitch is too fine. The more turns per unit of movement, the slower the machine. Cheaply made screws have a backlash that varies along the length of the shaft, which can also haunt you. The better machines use precision ground ballscrews which address these problems but simply cost more. And the better step-to-travel ratio ups the requirements on the stepper driver - this is one application for which you really need microstepping.
Finally, the details of the drive controller matter (The $50 raspi in the OP's list). Whatever is feeding the data to the stepper driver has to be real-time, unfortunately ruling out an RasPi. The most common way is to use Windows + Mach + pulse-generating USB dongle. A better way us to use LinuxCNC (which in turn uses RTAI kernel extensions) plus a parallel port. I've seen at least one 3D printer that simply parses the g-code in hardware which is really the most consumer friendly approach, but the list of desirable features for a CNC mill sends you back down the slippery slope toward a PC: for even small runs you want things like automatic toolchanging, tool radius and length compensation, workpiece offsets, rigid tapping... so far as I know, this is still a missing link for hobby CNC machines. Also CAM software, but that's a topic for another day.
(Score: 3, Informative) by WillAdams on Thursday June 11 2015, @04:33PM
Cutting non-ferrous metals: http://www.shapeoko.com/wiki/index.php/Materials#Aluminium [shapeoko.com]
Video: https://www.youtube.com/watch?v=NfYc35KeTEY [youtube.com]
The Raspberry Pi in the O.P.'s post would I believe be used to send G-code to the Arduino --- it's that which is doing the hard real-time calculation and machine movement. I'm amazed that it works, let alone work as well as it does. All opensource: https://github.com/grbl/grbl [github.com]