Is CNC Milling for You?
Milling machines use rotary cutting tools to carve a jewelry model from a block of wax; jewelers can then touch up or refine their models before casting. The number of axes in the machine can vary, with three- and four-axis machines the most common in the industry. Five-axis machines are available and can give the user more abilities and flexibility, but they’re more expensive, tend to be slower to mill, and require more work to keep the machine in alignment.
What You Might Want to Mill…
• Pieces with simple patterns or designs that have no undercuts. Any designs for which the cutting tool can come straight down onto the surface (if it is flat) or perpendicular to a band surface (on a rotary cut) are ideal.
• Items with lettering or that have designs with fine detail. Because mills carve wax, which burns out with little expansion, they can create sharp, crisp letters that won’t be compromised during the casting process.
• Pieces on which you want to do hand-carving work, such as engraving, before casting.
Things to Be Aware Of…
• Because the standard cutting tool has a taper to it, any straight 90-degree edges will have a slight tapered effect. This can be compensated for during the CAD design process by including additional material in those areas.
• Although mills are very good for carving fine, sharp details, there is a limit to the fineness that is possible. Even the smallest cutting tools have a small flat on the tip that measures 0.003 inch. While pretty small and not something easily detectable to the naked eye, it is something to keep in mind.
• Mills with fewer than five axes cannot easily be used to create undercuts on pieces, although such designs can be milled in multiple pieces and later assembled.
• Avoid carving very long, thin models on a mill. As the mill physically cuts away material, the wax will vibrate. Although all models require some form of support during the cutting process for stabilization, long, thin models require additional supports that will not only need to be removed, but can also break from the vibration.
• As with undercuts, most mills have difficulty creating hollow pieces. Milling designs in separate segments for later assembly may be possible with some designs.
• Although mills can run multiple models at a time depending on geometry and size, most mid-complexity and up pieces will need to be run by themselves.
• Although the technology has been around for a while, it can be difficult to find tech support, as many users and companies have moved to 3-D printing.
The Materials You Use
There are many suitable types of carving wax that can be used with milling machines, although typically those with higher hardnesses tend to perform better.
What You Might Pay
Machine costs vary widely depending on the number of axes and the size and complexity of the mill. Some basic desktop units capable of milling a range of materials can be had for as low as $2,200. Larger units with five axes capable of milling metal can run more than $100,000.
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