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Fabricate, Processes & Materials

CNC Capabilities

There are several different types of CNC machines and capabilities available on the Fictiv network, including 3-axis milling, 5-axis milling, and turning. Here's an overview of each CNC machining capability we offer and the different pros and cons of each.

Milling

If your part is any sort of shape other than cylindrical, or lacks rotational symmetry about some imaginary axis through the part body, then a mill is likely the machine for you.  With milling, the stock that the part will be cut from is usually a six-sided bar or sheet of material (though it can also be a cylindrical rod).  This stock is fixtured to the bed of the machine, and the features of the part are cut using a rotating tool such as a drill or endmill.

3-axis Milling

With a 3-axis machine, the rotating tool mentioned above can translate relative to the part in the X, Y, and Z axes (thus the name), but is fixed in a vertical (or horizontal, depending on the machine) orientation.  With modern CNC mills, the tool can also move in any combination of the 3 axes simultaneously.

Pros:

  • The most commonly available machine type on the Fictiv network
  • Relatively easy to program, and thus cost effective for most parts with prismatic geometries and features (such as holes parallel with the tool axis and pockets with vertical walls)

Cons:

  • Parts with features on many sides require multiple setups to machine correctly, which can get expensive in low volumes
  • Angular and organic surfaces take a long time to machine (read: costly) and sometimes require manual finishing and blending after machine to achieve correct geometry, especially if a feature wraps from one side of a part to another

5-axis Milling

A 5-axis machine is capable of the same movements as a 3-axis machine, but with added rotation about the X and Y axes.  It is usually the bed that rotates rather than the toolhead, though both types of machines do exist.  This added rotation allows for much more freedom when machining each setup.

Pros:

  • Capable of machining complex and organic geometries on multiple sides of a part
  • Features such as holes and pockets on different sides or at odd angles can be machined in a single fixturing setup.

Cons:

  • Not commonly available, due to the higher machine cost
  • Tedious and time consuming to program, so part cost can be very high at low volumes

Turning

For cylindrical parts such as pins, shafts, and spacers, or parts with general rotational symmetry, ‘turning’ them on a lathe is usually the simplest and most cost effective choice.  Contrary to a mill, a lathe operates by fixturing cylindrical stock, called a rod, into a rotating chuck jaw on the machine.  As this chuck rotates at a high RPM, so does the stock, and a fixed-orientation tool then translates along and across the stock to cut part features.

Standard Turning

Most CNC lathes are constrained as described above - the rod stock rotates continuously while a sharp tool either moves along the long edge of the rod or across its face, always centered vertically on the part.  Seemingly simple, this machine type is capable of producing many common engineering parts.

Pros:

  • Very quick to machine if part is perfectly symmetrical about its rotational axis
  • Great for external and internal threading, cutting axial/radial o-ring grooves

Cons:

  • Non-symmetric features (such as flats) and holes not aligned axially and centered on the rod face must be completed manually or with a separate setup on a mill
  • Short, large diameter cylindrical parts are hard to fixture and extremely long slender parts are prone to vibration and chatter

Live-Tool Turning

A CNC lathe equipped with live-tooling has all the capabilities of a standard lathe, but instead of relying solely on stationary tools, it can have rotating cutters such as drills or endmills, allowing for greater machining freedom and the introduction of asymmetrical features into the part without additional fixturing setups.

Pros:

  • A live tool lathe with C-axis milling/drilling (standard for live-tool) can cut features where the tool is pointing to or aligned with the vertical center of the part
  • A live tool lathe with Y-axis milling/drilling (usually in addition to C-axis) can cut features where tool must move above or below the part’s vertical center, such as off center holes or asymmetric features along the circumference of the part

Cons:

  • Less common and far more expensive than a standard CNC lathe
  • Y-axis capabilities are more rare than C-axis alone
  • Like a 5-axis mill, trickier to program and thus parts tend to be higher-cost

CNC Tolerancing

For all CNC materials available, we maintain part tolerances as outlined by ISO 2768 medium. This standard is based on linear dimensions; the bigger a dimension is (within a range), the looser the tolerance.  

Many of the machine operators in our network already adhere to a tighter standard, but this is the minimum we require and that you can rely on. Check out the table below for specified dimension ranges and their associated tolerances.

 

cnc tolerances chart

Main Takeaways

While it's helpful to understand the various CNC machine types and their capabilities, the good news is that Fictiv takes out the guesswork and chooses the right machine for every job on your behalf. In other words, there's no need to specify which machine type your part requires! For example, if a basic prismatic part is ordered, it will be sent to a vendor with a 3-axis machine, and a cylindrical part with radial holes and custom threading will be produced using a live-tooling lathe, and so on. 

As always, if you have any further questions about Fictiv's CNC machining capabilities, you can reach out to one of our prototyping engineers at help@fictiv.com.

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