Carving in the Round
Cut3D is a product by Vectric for CNC carvings that can be cut from one or many sides on a flat bed 3 axis CNC. While other of its products are designed for doing 2D cuts of flat objects or reliefs, Cut3D will create a command file (in GCode in my case) to create a 3D object from front and back, or multiple side cuts.
In my case, I also use it to create reliefs, though it is limited in this regard compared to programs specifically created to do that.
3D to Relief
At first, I was careful to create the relief completely in ZBrush. But it turns out that Cut3D has no problem turning multiple stacked objects in an STL file into a relief by ignoring the undercuts:
Two objects as created in ZBrush, one over the other.
In Cut 3D, as loaded, and a preview of the object as carved.
Slice and Dice
When you need to cut an object that is too deep for your material, or for the depth at which your CNC or router bit will cut, Cut3D will allow you to slice your object into flat segments to be cut individually, then stacked together afterward to build up the object.
Cut3D has trouble with meshes with more than about 1.5 million polygons. It's display updates slow tremendously once you get over about a million polys, even on a powerful 6x or 8x processor core computer. Chances are that Cut3D is not coded to take full advantage of this power--it may do everything in a single thread. So working with complex objects is a slow proposition, especially if you want to look around at them by rotating or zooming the display window. This is one are where Cut3D suffers a lot compared to its main rival in its price range--MeshCAM. MeshCAM manages the display of complex objects far more capably than Cut3D, though it is missing some of Cut3D's included features in other areas.
The trick is to simplify your mesh as much as possible in your 3D program before you bring it into Cut3D, of course. Also, if you want to cut out multiples of an object from a single piece of material, Cut3D will not allow you to do this within it. So replicate your object and build your internal tabs into the mesh within your 3D design software. Unfortunately, this works directly against Cut3D's limitations in handling complex objects by multiplying polys before bringing the mesh into Cut3D. My recommendation is to be strongly aware of feature sizes in your object relative to what will appear after machining when you're doing your initial design in your 3D software. Don't go crazy with the fine detail. And if you get tired of waiting for Cut3D to update its display, contact Vectric to request improvements, and maybe have a second CAM program to back you up in the meanwhile.
Know Your Dimensions
When planning your cuts in any CAM program, it's important to be aware of the clearances for your CNC when it's cutting. If you're going to be cutting deep below the nearby material's top level, know how far down your spindle can go without bumping into anything, and how far out the bit can be set without losing too much accuracy. Also, material dimensions are important. Cut3D doesn't have a material library to go with the bit library, unfortunately. But think carefully about how large it should be to let you get good registration between different sides when you're doing multi-sided machining. I tend to make the material long on the X dimension, then use pegs or rests that position the material properly when it is turned. One of my upcoming projects is going to be a fixed 90 degree rotary indexer to make "in the round" four sided machining faster and easier.
Originally I would re-set the origin on my CNC on each move of the work piece. Now I usually set the X and Y origin on a corner block off the actual material, with the material size exaggerated in Cut3D by a half an inch or so in the X and Y dimensions to compensate. To date, I've been using the origin at the corner of the material. I'm going to be changing to placing it at the center (once I create a new HAL file to match in EMC2) to make it so that I don't have to change the material size in Cut3D, while still allowing me to set my X and Y zeroes by points that are not on the material to be cut.
One of the nicest things about Cut3D is that it includes the animated preview with the program, rather than as an extra-cost add-on. Being able to watch this is almost as good as doing an "air cut" to get an idea of what the final command file is telling the machine to do. I've caught many errors without ever walking out into the shop by watching the preview carefully. The ability to change materials is nice, and to quickly change the view no matter how complex the original mesh, when you're checking out the design with someone else.
Cut3D is a great tool at the low end of the CAM price spectrum. It has its limitations, as one would expect when trying to get in at amateur level prices, but once you learn to work with it in what it does well, it produces great results. A lot of that depends on giving it data from your 3D software that it can work with, rather than just dumping it over without any preparation. Whether Cut3D is the tool for you depends on what you want to do. Unfortunately, their evaluation version only works with specific files that Vectric supplies. It's enough to check basic compatibility with your CNC, but if their files are not representative of your normal work, you might have to make some guesses as to whether it is right for you. A time or file count limited eval version would be nicer.