3D and CNC Routing

from Jim Lohmann

3-D cutting, machining, and sculpting can be used in many different types of projects. It is one of the most impressive capabilities a ShopBot CNC tool will bring to your shop. All ShopBots have full 3D capability and the high speed capabilities of PRS ShopBots make them excellent for efficient 3D work. There is a lot of confusion surrounding 3D and with how best to make it work for you and your type of application. This section is intended to provide you with an introduction to 3D and to clarify how you might to incorporate 3D features into your work. Understand at the outset that there are a lot of different ways to do 3D and there will probably be at least one that is right for you.

What 3-D Is Not

ShopBot CNC tools are all fully 3D capable, as are most CNC routers today [this capability is technically described as "3-axis interpolation," which means that moves are made smoothly in 3D space using diagonals and curves]. There was a time when the Z axis of some CNC's moved only when X and Y were not moving, or only had a single up and down position. These earlier CNCs were thus not capable of 3D carving and were referred to as 2- or 2.5-D tools. Now, rather than specifying the capability of a CNC tool, the terms 2-, 2.5-, and 3-D are more descriptive of the nature of the design side of a project; either what is done with the design software, or what the design software is capable of doing. Here's a little sample:
 

Clarifying Designing in 2-D or 2.5-D. If all we have is a flat outline of something we want to cut out, that would be considered 2-D. If we then added straight up and down movements of the cutter into and out of the material, we might now consider the project as 2.5-D. This 2.5D work starts off as a 2D design in principle, but during the process of creating the tool path or cutting file you will typically assign a depth or multiple depths for the tool's motion to cut features like grooves or flat pockets. When the software generates the part file, the instructions will first move the CNC tool to the assigned cutting depth (in the Z axis), then move the cutter through the XY tool path at that depth, and then return to the starting height with a straight pull-up. Thus, when the file is finished the cutting tool has moved in 3 dimensions (X, Y and Z), but all the X and Y axis motion is in a single plane and the X and Y axes stop when the Z axis plunges or pull-up. So, for the case of this example, the drawing and design process are fundamentally 2-D. Standard cabinetmaking would be a good example of such a 2D or 2.5D project.

Tool paths in 2.5D

V-Carving Might be All You Need. It is also common to consider 'V-carving' as a 2.5D design process. This technique uses CNC motion with a v-shaped cutter to give a classic chiseled look (also called chip carving) to lettering or other shapes that would traditionally have been carved by hand. The 2.5D description is appropriate because the design that you work with is still 2D in nature, even though the actual CNC movements that create the chiseling effect involve full 3-D, simultaneous XYZ motion of the cutter.

V-carving is a great way to add an impressive look to your lettering or sign work and decorative wood carvings. Importantly, because the layout process is still in 2D, it is relatively easy to create the designs, and from a production point of view v-carved letters can be cut fairly quickly.

Real 3-D Stands Up ... and Stands Out!

Full 3D CNC involves both designing in 3D and during cutting, simultaneous CNC motion in X, Y, and Z axes. In 3D, your CNC cutter tip follows paths at 3D angles or in 3D curves in order to mill or carve complex shapes into the material. In 2.5D, your cutter may have been moving in 3D in situations like v-carving, but you were still thinking (designing) in 2D. In order to do fully sculptural 3D, you are going to need to think and design in 3D. This is harder and frequently more expensive than 2D, but takes full advantage of your CNC tool's capabilities to produce fully contoured shapes milled to your specifications. The shapes that you can machine are nearly unlimited and adding even a small amount of true 3D to a project can uniquely distinguish it.

When considering working in 3D, it is useful to separate the process of design or shape creation, from the tool-path generation process. There are separate software programs for each, and only a few programs provide both capabilities. In fact, there are quite a variety of approaches for the design process because 3D designs are used in the world for many other purposes than CNC cutting.

3D Design: Consider the design process first. You will need to create the 3D shape of your concept in a 3D design system, defining the form that you want to cut. This shape is called a 3D model and the software programs that do this kind of work are usually called 3D modeling programs (sometimes 3D CAD). 'Modeling' is the right word here, because rather than drawing with lines, you will build up your 3D object by inserting and modifying basic 3D shapes. Note that visualizing and conceptualizing 3D shapes on a 2D computer screen is difficult and will probably involve your using new and unfamiliar computer graphics tools for manipulating objects and surfaces in 3D space. You should appreciate upfront that it is going to take a little time to get comfortable with.

You will need a program for doing your modeling. If you are unfamiliar with this kind of thing, Silo is a low priced starting point (@$109) that you might find fun. This is a nifty and comparatively easy to use program, but it really gives you a good feel for what is involved in 3D modeling. You might want to give it a try. As you get more serious about 3D modeling, you may want to consider the most acclaimed of the low-end 3D modeling programs, Rhinoceros (Rhino for short; @$995). 3D is still harder than 2D, but there is nothing bad to be said about Rhino when you are ready for 3D (additionally, it has 2D CAD capabilities and extensive add-on functionality). There is much more expensive stuff too, but we will leave it here and just say that one way to produce your 3D model is to create it yourself in a program like Rhino. [Note that a little further down, we'll consider other ways of coming up with a 3D model without doing the design yourself.]

3D CAM: Once you have a 3D model, you need a tool path. A 3D model defines the geometry of the shape that you want to cut, but it does not tell your CNC tool how to actually move over and around the model in order to cut the shape. The model does not know what size and type of cutter you will be using, how tight you want the resolution, what kind of directions you want to cut in, and so forth. So your next step is to bring your 3D model into a 3D CAM or tool-path generating program to create the Part File that tells your ShopBot how to actually cut the shape.

Using the 3D CAM program, you set up how you want to cut the part. For example, you lay out the part on the material, and knowing cutter size, you define the resolution and direction of the cutting passes. You can do other things in the CAM program that may not seem as obvious such as creating separate roughing and finishing passes or defining a machining border around an irregularly shaped part.

As with 3D design, there are a variety of CAM programs that can be used to generate tool paths from 3D models. ShopBot's come with a 3D CAM program called PartWorks 3D. With PartWorks 3D, you bring in a 3D model from a modeling program, define and generate a tool path, and output a ready to cut Part File. PartWords 3D is intended to be simple and straightforward. It is as close as you can get to doing 3D by pushing a single button (once you have a 3D model).

Regarding 3D router bits: The tapered (to 1/8th"), ball-nose, bit included in our Starter Bit Kit (also available separately from us or Onsrud) is great for 3D work. After an initial path is cleared at the cutting depth, the ball-nose cutter can be used to efficiently remove small amounts of material on fast passes back and forth across the material. This method creates smooth and intricate surfaces and takes advantage of the speed capabilities of ShopBot's PRS CNCs or earlier PRTalpha machines or PRTs upgraded the newer V4g Control Boards. [View VIDEO: ShopBot PRT with V4g Upgrade, cutting 3D relief project using tapered ball-nose cutter.]

Combining 3D Design and CAM: A Standard. A few software packages combine 3D modeling with CAM features. This gives you a more organized approach to doing full 3D work. An example of this approach is MasterCAM, which offers generalized set of packages for start to finish 3D CNC work (also capable of importing 3D models from elsewhere). MasterCAM is close to a standard with respect to 3D engineering or architectural work with CNC routers. Beyond MasterCAM there is an extensive array of 3D software oriented to CNC machine tools and mostly priced at considerably higher levels.

Combining 3D Design and CAM: Something More Unique and Creative. Many users of CNC routers are interested in intuitive methods for sculpting and carving in 3D and particularly for embellishing their work with 3D relief carvings, as might be applied to signs, cabinets doors, or furniture. Relief modeling offers a special kind of challenge because it is intended to convey a particular type of feeling for depth without necessarily being an exact replica of the depth of an object. Often with a relief carving the idea is to create the most realistic impression with a minimum of depth (as in the face on a coin). ArtCAM Pro is the one design program that is oriented to the challenges of relief work and for conveying depth or sculpting in 3D. It is oriented to helping a user shape a 3D relief, starting with only a 2D line drawing or bitmap image.
 

ArtCAM Pro helps you create (raise) 3D shapes from line drawings.

Final 3D model (on left) and close-up of  tool path (above).

By providing you with an extensive set of tools, ArtCAM Pro enables you to raise, round, slope, angle, texture, and generally shape the components of a 2D image into a compelling relief model (the example above uses a line drawing; in addition ArtCAM Pro has extensive tools for creating relief shapes from shaded bitmaps). No other program lets you sculpt like ArtCAM Pro. It is a complete 2D/3D CAD program capable of creating or importing drawings and models and having extensive layout and editing functions. In addition it is a full and extensive CAM package for generating 2D and 3D tool paths.
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Some examples of projects created in ArtCAM Pro

Doing 3D without Modeling Software

Now that you know about 3D modeling, an alternative you may want to consider is not doing the design/3D-modeling work yourself. We are not all artists after all, and even if you are so inclined, if you don't use the 3D design software frequently or have enough demand then you will not be very efficient with it. There are now a number of resources providing CNC-ready dimensional clipart or offering custom models made to your specifications.

There is, in fact, a lot of 3D clipart available on the internet,  many of these models are free or very inexpensive. You will typically need to bring these 3D files through a 3D tool path generating program such as PartWorks 3D in order to get a tool path. [See 3D links in our ShopBot CNC Resource List.]

The problem with the generic 3D models on the web, is that most were created for purposes (e.g. video animation/games) other than doing 3D machining. They are often too low a resolution for smooth carving or have errors or inconsistencies that make machining difficult. The models may also not be well suited to scaling to different sizes, which is something you will probably want to do. A good model has the detail needed to be effectively cut in small or very large sizes. [This is a similar problem with 2D clip art found on the web, which is often not suited for 2D CNC cutting; see the Vector 2D Graphics collections for CNC-ready 2D art work.]

A better option for 3D, still at a relatively low cost, is to purchase 3D models which were developed explicitly for 3D CNC cutting. Vector Art 3D is a prime provider of such files. Their parts are all developed to machine well at relatively low depths of cut. You can use the free CAM program that is provided with the models, or use PartWorks 3D to create the exact tool path you need for cutting the models. Their models can also be used as modeling components to make more complex designs in programs such as ArtCAM Pro, EnRoute Pro or Rhino. As a point of information, a majority of the Vector Art 3D models were developed in ArtCAM Pro and show the power of the relief modeling features of that software.

from Vector Art 3D and Beckwith Décor Products

Vector Art 3D offers an extensive library of 3D models to select from and the list is continually growing. They also offer some collections of their clipart which are a very economical way to buy a lot of models at once – these collections can be purchased directly from ShopBot. In the event you need a custom design or a variation on their existing library then you can contract for a model developed specifically for you. This can be done through Vector Art 3D – they have a selection of skilled digital and virtual artists who can produce a model to your specifications.

from Vector Art 3D, custom model  for ITC Millwork

There are also a growing number of specialist providers of CNC modeling services (we're working on a list). When you consider the value of your own time and your inefficiency at using the 3D modeling software (or if indeed whether you have a copy or not), you will appreciate that commissioning a custom 3D model can actually be an economical way of getting a special 3D component into a project that you are working on.

from Vector Art 3D and Balch Signs

Doing 3D without using Modeling OR CAM Software: A Couple of Shortcuts to 3D

So far, we've discussed the primary and direct approach to doing 3D; creating a model with a 3D modeling program (or purchasing one) and then bringing the model into a CAM program to specify and generate the tool path and output a Part File. However, there are a couple alternatives to this approach which you may find handy for certain types of projects. They can actually be accomplished directly with the ShopBot Control Software. Think of them as shortcuts to 3D that can be accomplished without any additional software.

Using Bitmaps Directly. A first approach is to create 3D contours from a bitmap image using ShopBot's Bitmap Converter, a function that is included in the ShopBot Control System software. This converter, which is called up with the [FC] Command, will turn the grayscales of a bitmap image (.jpg or .bmp) into cutting depths and create a tool path that can be immediately cut. You modify the proportion of each axis in order to control the shape of the image. This technique can also be used to produce lithophanes from photographs, though you will have to fuss to get the depths exactly right for handling the light. [Photo V-Carve will handle setting up lithophanes a little more readily, and it also offers a v-carving approach to transferring bitmap pictures into CNC carving.]

Digitizing Probe. The second way to produce 3D shapes without software is to digitize an existing object or part using a digitizing probe. The ShopBot 'Copy Machine' Virtual Tool that is included in the Control System Software will help you carry out the digitization with an optional probe and create a ShopBot Part File that is ready to cut at the end of the process. You can use a digitizing probe purchased from ShopBot, a probe from another manufacturer, or if your part is electrically conductive you may be able to just use a metal stylus like a paperclip. You can probe to reproduce the 3D shape of a part, or you can probe to get the 2D outline of a part. The probe is simply a switch that is triggered when the tip of the probe contacts the surface of your sample part. When digitizing a 3D part by probing, your ShopBot will methodically move the probe tip in a raster pattern, carefully contacting and recording the position of each contact in order to reconstruct the shape of the part for cutting.

The probing functions of the ShopBot Control software allow you to save two types of file. You can save a Part File of actual ShopBot CNC instructions that is ready to cut at the end of the probing process. Or, if you need to do some modifications to the shape before creating your final file, you can save a file of 3D points or a polyline that you can use directly as primitive entities within 3D modeling software. Alternatively, you can process the 3D points into a 3D surface file using the 'Probe to Surface' Virtual Tool in the ShopBot software. The shape can then be brought into 3D modeling software such as Rhino for further editing, manipulation, or processing, or directly into a CAM program such as Cut3D for specifying and generating high quality a 3D roughing and finishing toolpaths.

Some pretty amazing things can be done with digitizing, and you won't even need to muck with software. You might also consider sending your digitized model to someone to modify or refine the design, or even consider sending your physical model out to be digitized by a digitizing service. In either case, you may find it an efficient way to get to the 3D carving that you need without getting involved in what can be very tedious modeling work.

Some Limitations of Typical 3D on a CNC tool ... and a Source of 3D Confusion (3-Axis CNC Tools vs 5-Axis Tools and ShopBot's Rotary Indexer, a 4-Axis Tool) The above discussion summarizes the basic methods for doing 3D work with a standard ShopBot or other CNC. But just to make things a little more confusing we'll add one more level of complexity for you to consider, doing in 3D work in 4, 5, or more axes of motion. Most CNC woodworking tools are what we call 3-axis tools. They move a cutter in the X, Y, and Z axis. They machine or carve in 3D by moving the tip of a cutter in these three axes, usually with a back-and-forth (rastering) motion in the X and Y axis (or a contouring path related to the shape of the object) and a simultaneous up and down action in the Z axis. The cutter itself remains in a fixed vertical orientation. The cutting is done by the portion of the cutter that is in contact with the material. This type of 3D work is fundamentally 'relief' machining. It gives you a 3D shape, but does not allow for 3D shapes of the sort that have ledges or requires undercutting, or any kind of cutting/machining that can't be done from vertically above and perpendicular to the XY plane. 3D objects that require machining from the side or bottom require another strategy. Sometime you can accomplish this sort of effect with slicing techniques or by rotating the object and machining from different angles. Cut3D, for example, will generate coordinated toolpaths for machining an object from 2 or 4 sides. But such solutions don't directly address the problem, which is that you can't move the cutter around to the side or underneath. 3D animal cut as two halves and joined (from Baycraft Designs) Product prototypes cut as two halves and joined (from Think Design, Humancentric Tech) CNC Tools with More Movement Capability.  By adding more axes of motion or rotation, the orientation of the cutter to the material can be changed, and this can allow more accurate and efficient 3D shaping and can offers production of parts that have more contour. Added axes also permit cutting into a part from the side as well as diagonal drilling. ShopBot's software and control system is 5-axis capable (with the [VD] Command you can turn on additional axes), even though our standard tools have mechanical capabilities for only 3 axes of motion. 5-axis tools have historically been very expensive because of the difficulty of creating 5-axis controllers and the mechanical problems of keeping the extra axes rigid and providing enough space for the cutting head to move. 4 Axes.  ShopBot's Rotary Indexer allows machining of parts in the round. The indexer is like a smart lathe. It makes rotating the part the 4th axis of control. This means that you can profile objects in the way you might with a traditional lathe, but you can also do ornamental turning and free-form carving in the round. [See Indexer] from Jim Lohmann Parts made on Rotary Indexer from Bob Dodd 5 Axes.  Over the last several years, ShopBot has tested several prototype 5-axis tools and currently has a 5-axis head in development. This head provides an extra 2 axes of motion to any of our 3 axis PRSalpha tools. You can think of the extra two axes as the wrist at the end of an arm. With a 5-axis tool, cutting and drilling can be done from any angle. More importantly, tangential machining can be done whereby the end of the cutter is always perpendicular to the surface being contoured. This technique produces smooth and efficient machining.  ShopBot's 5-Axis CNC's will be fitted with 2hp spindles and are intended for machining soft materials such as foam and soft wood. They will should also be effective at trimming parts where full access from varying angles is important for preparation of the part.  Prototype 5-axis head, fitted to PRTalpha at Boeing   [View VIDEO: Prototype 5-axis ShopBot Benchtop Tool in operation]

We hope this introduction to doing 3D with a CNC tool has been helpful to you. As with many aspects of CNC, 3D is something that you can do in many ways -- there's probably at least one approach that suits your project, your style, and your budget.

If you have any questions about how to get from a 3D concept that you've got to producing the part with a CNC tool, please feel free to give us a call. We may not have the complete answer, but can get you pointed in the right direction.

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