CAD/CAM Jewelry Primer
From The Tabletop Machine Wiki
written by Bob Lombardi
Introduction
If you are new to the whole world of CNC machine work on small machine tools, I’m sure you’re going to have some confusion in getting started. The terminology itself can be overwhelming if you’re just getting started. To begin with CAD/CAM means “Computer Aided Design/ Computer Aided Manufacturing”. Some folks say Computer Assisted instead of Aided. It’s using a computer to design a model of the jewelry piece you want to make, and then using a computer (usually a separate computer) to help you make the piece. For example, figure 1 is a simple ring that I’ve actually made with the CAD/CAM process. The ring was first designed in a 3D modeling program, instead of with pencil and paper. That was the CAD part. When the design was finished, it was turned into a file format that could be read by a variety of programs or machines that turn the outline of the ring into a set of instructions that tell a machine tool program how to move the wax under the tool to produce that design. That’s the CAM part. We’re still not done. We need a third program that turns these machine tool instructions into electrical signals to command movement of the piece under a cutting bit. This is typically done with a CNC Control program – CNC is Computer Numerical Control - of a machine tool. There are other ways to do this, too. Industry has developed a group of techniques called Rapid Prototyping. More on this later.
So why would anyone want to do that? Isn’t it easier just to carve a wax? The answer isn’t easy. If you are a talented wax carver, or the design is simple, yes it probably is easier. In the hobby area, folks tend to do everything. Professional jewelers don’t. Some specialize in wax carving. Some specialize in casting. Some specialize in stone setting. Hobbyists seem to think we should do everything. One of my goals was to be able to carve the things in wax that I can “see” in my mind. I thought I could get the computer to do it easier than I could learn to carve – and do everything else – myself.
The industry is moving in this direction for a lot of reasons, but their main reason is that it is more profitable. A problem jewelers have is producing a custom design for a customer, fabricating the piece, and delivering it, only to find that the customer isn’t happy with it and doesn’t buy it. One of the advantages of the CAD/CAM approach is that you can produce a very lifelike picture – called a rendering – of what the final piece will look like well before you actually make anything and customers are less likely to reject the work. Photorealistic rendering is an area I haven’t concentrated on much, since I’m trying to produce jewelry, not pretty pictures, and I’m not trying to sell to anyone. I won’t talk much about photorealistic rendering. Here is a rendering that is not photorealistic, but shows what the piece should look like:
One of the things that got me interested in doing this was seeing these titanium rings produced by Dan Statman at http://members.rennlist.com/statmandesigns/ , when I first started getting interested in small machine tools. These were all made under CNC control with a Sherline mill. Long story short, I have made a ring like one of these for myself. It was part of the process of getting here.
So What’s Involved in Doing This? What Do You Need?
- A mill or machine tool for carving the metal or wax. The wax must be moveable under computer control, so this is called a CNC mill. You can buy the complete Sherline CNC mill package, ready to use, or Sherline CNC centers from a variety of suppliers.
- A piece of electrical hardware that converts motion commands from a computer into voltages that run motors inside the mill. A motor controller.
- Software to send these movements to a piece of electrical hardware that controls the mill. A CNC controller program.
- Software to design the piece. 3D CAD software.
- Software to convert the design into tool paths, which represent machine movements. CAM software.
- In addition to all the normal things you’d use to fabricate the design, you’ll need a way to hold the wax (or metal) while you machine it.
Getting Started
Step 1 - The Machine for Carving Wax
I start here because the hardware you’re using helps determine the software you need. The machine most often used is a small version of a milling machine. The mill has to have the accuracy to return to a position it had previously machined within about .002” even after running for hours. Surprisingly, this is not a very difficult requirement. There are software methods of compensating for some machine hardware inaccuracies, such as backlash. The motor speed you need is somewhat higher than you use for general metal working. For fine detail carving, you will use engraving bits that are only a couple of thousandths of an inch across. With such small bits, you need to spin them at high RPMs 10,000 to 20,000 or more, and some people use their Foredom handpiece or Dremel in their mill. If you spin with a slower motor – 4000 RPM or so, you can still do this sort of carving, you just won’t be able to move the wax being carved very fast.
A milling machine has a motor that turns a tool bit and then controls that move the work in 3 or more axes under the cutting tool. The 3 axes are the X, Y and Z coordinates of 3 dimensional objects as taught in high school math, but math knowledge is not really needed to use the software and hardware. Each axis has its own motor to control motion of the axis. One drawback of a 3 axis approach is that many rings have a natural shape that’s symmetrical in rotation around the finger. This is most easily accomplished with a 4th rotary axis, usually called the A axis. My milling operation has never involved any more than 3 axes of movement. When using the rotary axis, I don’t need to use my Y axis, so I unplug those wires and plug them into the rotary axis stepper. For some machine work, you need to use all 4 axes and that requires an electrical interface that’s different from the one I’m using.
I’m using a Sherline mill, this is a Sherline group after all, but others also work fine – maybe better. The two main alternatives to a Sherline are produced by Taig and Prazi – both companies have excellent reputations, and each machine has its own advantages or disadvantages with respect to the others. The big design companies we’ll talk about below use mills costing on the order of five times the cost of a complete CNC Sherline, or more. Here’s my Sherline mill by itself. The mess is pretty typical of how things look in my shop between jobs. That thing on the upper left is the rotary table with its stepper motor facing you:
(Those two green wires hanging off the motor controller are ground wires for the box the CNC Training Center came with – I switched over to the modern Sherline motor mounting system from the proprietary system this firm used). Here’s a closer look at my Sherline rotary table with its stepper motor.
Here’s a close-up of my machine cutting an aluminum practice piece that resembles one of Dan Statman’s titanium rings. In this case, the work is held directly in a 3-jaw chuck on the mill’s rotary table:
When I started down this road, I had no experience with machine tools, and had never touched a Sherline mill – in fact; I’d never touched any milling machine in my life. Along the way, I had to learn a lot about how to machine things, how machine tools work, how to hold the piece while you’re working on it, and a hundred other details that you need to know to make that first piece of jewelry. I say this to both encourage you that you can do this without having a background in machine tools, and to let you know that there is a long learning curve to climb.
The motion control comes from commanding stepper motors to count some number of steps in each direction. This is known as “open loop” control, because there is no feedback to the system telling it if the motor moved the desired number of steps. The alternative, of “closed loop” control, uses feedback and servo motors instead of stepper motors. Since there is feedback control, the system can be more accurate, and faster, but the feedback path adds cost, so the closed loop system is typically more expensive than the open loop approach. There are advantages and disadvantages to both approaches and neither approach is right for everyone. It is said that no one who switched to servo control has ever gone back to open loop control.
Most people have heard of a lathe and there are wax lathes available. Lathes are not extremely useful for jewelry making, but are quite helpful to have around. My introduction to using machine tools was with a Sherline lathe that my wife got me for Christmas a few years ago. Lathes make parts by moving a fixed tool against a rotating part, instead of rotating a tool and moving the part, like a mill does. The difference is subtle though, and many things that are done on a lathe can be done on a mill. I use my lathe for boring the wax ring blanks to size before fixturing them for the mill.
The important thing to remember is that your machine can only touch the wax in a single point. In the case of a ring rotating around the finger hole, it can only be touched along a radial line into the center of the ring. If your design has features along the sides of the ring that can’t be touched by moving in this direction, you need to reposition your work so that the mill’s cutting bit can get to that surface.
Step 2 - Signals Into Motion
Inside the mill enclosure there is a piece of hardware that turns signals from the computer into voltages that run the stepper motors, along with a power supply to run it and some power switching circuits. The stepper motor controller board I use is from a small company called Xylotex. There are many companies that supply stepper motor controllers to a burgeoning hobby market. Other companies, like Gecko, sell controllers that work with Servo systems.
Step 3 - The Source for These Signals
Finally, there is a program that controls the CNC mill through this interface. I am using a shareware program called TurboCNC that works quite well on old, “spare” computers that you can pick up for a song – or for free from the folks who might be ready to toss one out. There are, again, other alternatives, each with their own advantages and disadvantages. These programs run the file of tool paths produced by the CAM software and turn them into signals going over a printer cable to the stepper controller in the mill enclosure.
Step 4 - Design Software
The most important requirement for the software is that it should allow you to model the part as a 3 dimensional object. There are subtle differences between solid modelers and surface modelers that I really don’t think are important to us. The design software can be the most expensive thing you buy.
The program that the Lapidary Journal focused on is one called Gemvision Matrix. It is hard to say what this program costs – I don’t want to call one of their sales reps. Their website says it is available: "lease Matrix software and training for 2 people for as low as $245.00 per month”. Based on other software I’ve seen, I would guess it sells in the $10,000 price range. That puts it out of my ballpark immediately, despite its amazing capabilities. Here are a couple of renderings from their website, http://www.gemvision.com/html/products/matrix/matrix.html
This first one is an example of what I think is relatively easy to do in CAD/CAM – because of the repetitive pattern, but hard to do carving wax by hand:
This ring would be hard to machine because in addition to the areas cut into the surface that require a rotary axis, there are machined features along the ends of the ring. That means it will have to be machined in three operations: one around the rotary axis and one on each end face. It would take extreme amounts of talent to carve free hand. Also on their site is a more conventional ring that might be buildable either way:
Another very popular program is one called Jewelspace by Caligari. Jewelspace is more reasonably priced, but still pretty expensive at $2000. You can see the options available at: http://www.jewelspace.net/products/jewelSpace/js3/default2.asp
Both of these programs are aimed at professionals and small factories. Jewelspace and Matrix both contain toolbars of components, ring shanks, stones and other parts, that allow you to assemble a piece by picking parts out of a menu and scaling them. To design a ring in Jewelspace, say, you would pick a shank or band style, scale it to the desired size, pick a material, pick the stones you want and assemble it on the screen. The obvious advantage to this is that it speeds your work. The only disadvantage of this approach is that you tend to see repetitive designs this way – all ring shanks tend to look the same. Still, it is like having ready profiles of half round wire and bezel wire, like we use in silversmithing.
Interestingly, both of these programs appear to be based on another. They are component sets and interfaces developed for Rhino3D, the program I’m using. Rhino is a general purpose 3 D modeling and CAD program used for designing ships, shoes, electric drills and jewelry. http://www.rhino3d.com Here’s a couple of designs from Rhino’s gallery. First a pretty conventional ring:
This ring’s only unique aspect is that it will have to be cast in sections and soldered together to achieve the mix of yellow and white. For your interest, here’s a piece I’ve looked at many times and wondered how I could actually fabricate. I think carving the stone would be the hardest part, although fabricating the white/yellow gold stripes would be a challenge to me, too:
Since I was familiar with AutoCAD from work, that was my first thought for approaching the 3D design problem. AutoCAD, though, was way out of my price league. I then went to another conventional CAD program, TurboCAD, primarily for its low price. For some reason, I could never grasp how to manipulate 3D objects in TurboCAD, although I tried for a long time. Once I downloaded the Rhino demo, I loved it. It works closer to the way I think than anything else I’ve seen. Here’s a view of the Rhino default desktop as it would look while designing something.
You can see there are 4 views of the ring, including a perspective view that is fully 3D, and moves around as you try to examine it from different angles. You can see toolbars all around the workspace that allow you to pick a tool by a graphical depiction, or you can type a command at the command line at the top. Like most modern programs, there may be four ways to do the same thing.
Rhino is enormously powerful, but that power comes at a cost of a steep learning curve. There are no standard jewelry components to put into your drawing, so every part of every design must be drawn – at least the first time. You can import drawings into your drawing, so you can make a shank, decide you want to keep it, and save it as a component to bring in to your designs later.
Rhino is sold by a contributor to the Sherline groups, Andrew Werby at http://www.computersculpture.com/ at the best price I could find. Andrew is a great guy, a great resource, and worth talking to and dealing with.
Finally, there are many options down this road. Just because I found Rhino easiest to use doesn’t mean you will. Good 3D software tends to be expensive, though, so look around carefully. Pete Brown has a good chart listing various software options on his website, http://www.irritatedvowel.com/Railroad/Workshop/SherlineCNC.aspx midway down this page.
Step 5 - Converting the Design to a Machine-Usable Format
This step is the CAM part of CAD/CAM. Rhino (or the other programs) will need to save the design in a format that a CAM program can read. While there are several, I’ve been using Stereolithography format. That means I could send my designs to a service company and have them build me a prototype with stereolithography instead of carving wax on the mill.
There are programs that do both the CAD and CAM – they generate the CAM file directly. I looked at two of these (Vector and BobCAD) and didn’t feel comfortable with the interfaces. I settled on a program called DeskCNC that seems to do everything I need. There are others. DeskProto is an excellent program that has many features you’ll like. The exact feature set you need depends somewhat on what you’re going to do. Many programs only support a 3 axis mode. The more intricate and expensive programs allow a 4th axis. If you have a rotary table, you need this. DeskProto’s high end version has a special routine set that allows you to turn a work piece over, so that you can do multiple sides of the same part – like that thousand stone ring above.
Here is a picture of a simple ring in DeskCNC showing the rotary toolpaths used to carve it from wax.
DeskCNC supports a rotary axis, very useful or essential for rings and other designs. The deciding factor for me was that DeskCNC costs under ¼ of what DeskProto costs. Over the course of my first year experimenting with this, I realized that the most effective way to use the program was to generate multiple tool passes with different sized mills. For the simple designs, like this one, a single pass with an engraving bit will work. For more intricate designs, a first pass with a 1/16" ball end mill, followed by the engraving bit, seems to produce better waxes.
Now What? - A Lot More Steps to Master
Now that you have all the pieces, you’re only at the starting point. You need to be able to hold the wax, carve the wax, prepare it for casting, cast it, clean it, polish it, set the stones, and all the tasks a regular casting requires. I will omit the things you do in a conventional casting class and focus on the machine tool aspects, but it’s something that I’ve tended to lose sight of. If you can’t do a pave or a gypsy setting, for example, don’t think this will make you an expert. You can CNC carve a great deal of detail into the wax – perhaps the holes for a pave setting – but it won’t make you a goldsmith.
I should add that there are other approaches to making the wax to cast. Some service companies use “stereolithography” to build up the model. Stereolithography is one of a group of “Rapid Prototyping” techniques that industry has come up with in the never-ending quest to provide products faster. The main difference between stereolithography and using the mill is that milling is a subtractive process – you start with a block of wax and cut away the parts that don’t look like your design – while stereolithography is an additive process. These systems take your design and generate curves for a laser beam to follow. The laser is shined on to a special liquid that solidifies when the laser hits it. The thin shell that was just formed is then retracted under the surface, usually by stepper motor, and another profile hit by the laser beam. In this way, it builds up a hollow shell of your design in this plastic. These machines are still pretty expensive, as I understand it, and the service companies do all the handling of a design for you. You can email them a design file, send them your credit card number, and get back a plastic model ready to burn out and cast.
Like everything else, there are advantages to both additive and subtractive approaches. There are some things that can only be built by stereolithography, but I can’t think of designs that can only be built with a mill. Still, you’re here on the Sherline list, so I’ll assume you have (or probably will buy) a Sherline mill, so that will be the emphasis.
Fixturing and Holding the Wax
Once you get all this hardware and software assembled, you still need to learn things. A deceptively simple question: how do you hold the wax? It has to be very accurate and repeatable. Having a mill that gets your cutting bit within .0001” of where it needs to be doesn’t do you any good if the wax moves .01”. You don’t want you holding system to crush the wax, and you don’t want the wax to wander around during machining. This area is terribly important and I've probably not paid enough attention to it.
For simple rotary designs (rotation around a finger axis), I have found that I can turn a support rod of aluminum or something harder than the wax to hold the wax in place on one end, and hold this support in a chuck for the mill. I then melt some sticky wax on to the seams between my wax blank and the support. This generally holds very well, allows use on a rotary table, and access from both sides. For something like a pendant that is largely flat, you can use a flat block of wax and hold it using machinist’s techniques. Hold downs, toe clamps, or a milling vice are all things used to hold metal while milling it and will easily hold wax. A simple way to ease the task of holding the wax is to start off with a much bigger piece than you’ll need! Extra wax on the ends makes it easier to clamp or melt the wax and not damage the piece you’ll eventually cast. Compared to wasted time, wax is cheap!
There are commercial systems available that hold the waxes in a variety of ways. I think you should not limit yourself to one method, but use the method that works best for the piece you’re machining. For example, a company called ProtoWizard ( http://www.protowizard.com/pwmain.html ) has a fixture that holds the wax in yoke that allows machining from both sides. This would be ideal for milling into the ends of the ring design, like that really ornate one, above. The hexagonal shaped shaft is ideal for holding in a 3-jawed chuck on the mill.
A large percentage - potentially all - of the things you will want to machine need this sort of three sided milling. A flat piece of wax can be held in the jaws of a 4-jaw chuck and the wax milled as top and bottom halves of the design. These halves are then glued together with superglue (cyanoacrylate) and the edege rotary axis milled. You can design a center support into the ring in your 3D design software, split the ring into halves and produce multiple files for your CAM process.
Here’s a photo from Pete Brown’s web site, CNC machining wax held in a mill vice, for a railroad train model he’s working on. (Pete, by the way, has the best website name I know: www.irritatedvowel.com. This picture is at: http://www.irritatedvowel.com/Railroad/Workshop/SherlineCNC.aspx ) A pendant or brooch can start this way.
Wax and Cutting Tools
You can use the waxes you would use for hand carving. I personally think a harder wax is better. You’ll never get wax as hard as metal and you can easily mill aluminum, brass or mild steel on one of these machines. Harder wax takes fine detail better. For hand carving, you trade the detail you need vs. how hard it is to work. That trade doesn’t exist in CNC.
Although I haven’t tried this yet, machinists use wax for prototyping routinely, and it isn’t from Kerr or the other jeweler’s supply companies. A major brand is Freeman’s Machinable Wax, and that sells for quite a bit less than blocks from Kerr or Matt.
For small engraving bits, you can grind a well centered point onto a brass rod, or buy regular engraving bits. I’ve bought some engraving bits that are solid carbide. I broke one and was able to re-sharpen it by making a fixture for my Facetron that holds the bit at the desired angle to the lap. For other shapes, like general roughing of the wax, a 1/16” ball end mill can be bought for a few dollars from Enco or the machine tool dealers. High Speed Steel bits will last forever in wax.
Final Touch Up – By Hand
Just like you pretty much need to finish all your handmade waxes with Wax Brite (or equivalent); you will probably always need to do some final touch up of the wax by hand. I have not tried Wax Brite because I didn’t want to compromise hard edges in the pattern I was making – I used sandpaper. Hard wax handles well with files and sandpaper. Milling tends to leave fine lines across the pattern, and a little 400 grit sandpaper (followed by finer paper) is easily 20 times faster than going over the pattern multiple times on the mill. You can see these fine lines in this picture.
Conclusion
You’ve designed a piece, converted the design to a solid model format, turned into tool paths, fixtured the wax, machined it, maybe re-positioned and re-machined the wax. Congratulations. At this point, you’re ready to add a sprue (which can be done during the 3D design phase) and cast it like any other wax.
CAD/CAM won’t make you an artist and it won’t make you a jeweler. You still need to be able to cast the piece, set the stones, polish out, and all the other things you do in production. Like any other computer design field, you can certainly design things that can’t be built in any realistic way. Just watch a few computer-animated car commercials, or sci fi movies to see what I mean. It is surprisingly entertaining to watch the mill carve out your ideas as you wander around, sip coffee, or work on something else.
I hope this is helpful to beginners in CAD/CAM jewelry production. I’ve borrowed images from all over the web for this effort.
References and Resources
The best starting place is where this information is stored:
http://groups.yahoo.com/group/SherlineCNC/?yguid=149942318
The SherlineCNC group on Yahoo! groups.
Sherline Corporation has everything you’ll want to know about their machines: http://sherline.com/
There are many good sources for Sherline systems online. I’ve had good luck with http://www.discountcampus.com/ and http://www.tabletopmachineshop.com
The Xylotex stepper motor controllers, kits and more: http://www.xylotex.com/
TurboCNC, http://www.dakeng.com/turbo.html is the best shareware option available. Register it if you use it, it’s a great deal.
Rhino is at http://www.rhino3d.com/ and is sold by Andrew Werby at http://www.computersculpture.com/ among others. Andrew has a great page of links to suppliers that are there to help us (or sell us stuff… if that’s different) at http://www.computersculpture.com/Pages/Index_Links.html
As you’re learning how to use your mill, you’ll probably do other things with it. DESKAM gives away this program http://www.deskam.com/deskengrave.html to the community. It works great.
Another very worthwhile source is Fred Smith at http://www.imsrv.com/ Fred sells servo controller systems, complete systems and everything you need at http://www.imsrv.com/deskcnc/bench_top_cnc_systems.htm IMSRV also carries Vector CAD/CAM (http://www.vectorcam.com/) , the program that has the distinction of being selected by Sherline for inclusion with their machines (actually, a limited use version of only the CAD program). I may have given this combination short shrift in this document, so I urge you to look it over.
One the first people whose work I was inspired by was Dan Statman. http://members.rennlist.com/statmandesigns/ Dan has shifted from Sherlines to his own design CNC mills, probably due to the special problems of machining titanium. It can be done on the Sherline, but Dan used to talk of burning out Sherlines at pretty high rate.
Another of my inspirations was Roy Goodell at http://www.5xj.com/index.html Roy uses a CNC mill that appears to be his own design, and includes pictures at http://www.5xj.com/cnc/cnc.html
