Thursday, January 24, 2013

3D Printer and CNC

3D printer is all the rage recently. I got interested and decided to build one for my own amusement. At the same time, I have always been fascinated by CNC machines.

There are a lot of similarities between 3D printer and CNC. For example, they both move in the X/Y/Z Cartesian space. They all result in a real object (one by cutting, and one by building). Because I do not have a lot of space in my garage, I wanted to build one machine that may be easily converted between a 3D printer and a CNC machine.

In order to build such a machine, it is helpful to look at what makes them different. There are indeed a few important differences:

  • CNC needs a lot of sideway torque, while for 3D printer there is little (keep everything close to the cutting plane is part of the reason that most CNCs have limit Z clearance and Z range) ;
  • 3D printer needs more Z movement and Z clearance, while for CNC there is little (because for CNC there are only so much cut needed in Z anyway);
  • 3D printer head in general moves faster than CNC head (cutting versus depositing).
It is an easier to approach this from some existing designed or plans. Because of the above differences, I felt it is probably easier to look at the CNC kits first. After browsing the Internet, I found a rather comprehensive list of low cost DIY CNC kits.

While many of these may be converted to 3D printer, one of them suits my need particularly well. It is the ShapeOko design. What I particularly like about it is that fact that it has a combined X/Y/Z head. A lot of other low cost designs has a X/Z head with a Y work bed (in other word, the head moves in X and Z direction, while the bed moves in the Y direction). For a plane CNC operation, both has its advantages. But for converting to 3D printer, the X/Y/Z head has a distinct advantage. One of the main issue to consider for the convertible machine is that the 3D printer needs a larger Z range. With the combined X/Y/Z head (particular with the ShapeOko design where there is no built-in work bed), the work bed can be lowered to allow adding more Z range to the working area.

The fact that ShapeOko design has a lowest kit price does not hurt also. I do feel that the design is a bit flimsy (to achieve the amazing low cost), but I can strengthen that later. I also have concerns about the belt linear driving mechanism, and I like the rods better. But in their video, it seems that it can handle most light duty cutting job fine, so I decided to give it a try.

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