Finishing: Tips for CNC Systems

Knife cutting
A CNC router’s knife cutter is ideal for use with thin or soft substrates because it involves none of the material removal inherent with routing. Thin cuts are especially helpful for highly detailed projects or when a large number of prints must be cut from the same sheet. Using CNC software, the router operator can ‘nest’ a large number of parts or cut-outs very closely together.

One of the main advantages of an automated cutting system is the ease of switching between various knife attachments. The most common types include kiss cut, drag and oscillating knives and there are a few other options for very specific applications.


CNC machines can offer both router and knife options, as indicated here.

If a sign shop is creating vinyl cut-outs, decals or other products where the operator only needs to cut through one layer of material, then the kiss cut blade is the ideal choice. It is spring-loaded and automatically adjusts to the material being cut, so there is never a risk of cutting through the backing layer.

If instead the CNC table operator is cutting a thin material but needs to cut all the way through, then a drag knife is a better option, as it can quickly pass through all layers.

For a shop that deals in large volumes of thicker soft substrates, such as foam and rubber, oscillating knives are the best bet. Most are available in lengths of 10 to 100 mm (0.4 to 4 in.), depending on the shop’s needs. Variations include round-tipped oscillating knives designed to cut cardboard, rubber and softer materials, along with flat-tipped knives designed to cut leather and other fibrous materials.

Thicker materials create more drag when being cut, due to increased friction. Foam and rubber also naturally cause high friction, even when they are thin. The oscillation of the knife can help overcome this friction, resulting in a smoother cut and reducing the chance of the material being bunched or ripped.

Two other specialized knives can come in handy for sign shops. The V-groove knife, also known as a 45-degree knife, is used to cut grooves at a 45-degree angle in framing and display materials. This allows operators to then fold the two edges together to form a clean 90-degree angle to quickly create frames or displays for signs.

Finally, the creasing wheel is handy for signmakers who need to create point-of-purchase (POP) displays and other structural projects using cardstock, foamboard or other cardboard-based materials. The wheel creates sufficient pressure for indentation and folding, without puncturing the material.

If a sign shop specializes in thicker or stiffer substrates, then a CNC router is most likely the best machine to use for cutting. Depending on its configuration, a router will let operators cut a wide range of materials, from wood to aluminum, at various thicknesses and speeds.

In addition to choosing the right router for a sign shop’s needs, it is also important to use the appropriate router bits, based on the type and thickness of the material and the desired edge quality. It is extremely worthwhile to spend extra time and money to ensure proper bit selection from the beginning, to get the most out of the system.

Each material has its own ‘sweet spot’ with regard to optimal cutting parameters, so there is no single right answer in terms of feed rates and routing speeds, although there are some general rules that should be kept in mind. Below are some best practices for selecting routing bits and tools for some of the most common sign materials. Ultimately, however, it is essential to reference the router and bit manufacturers’ guidelines to ensure the best cut quality and the maximum longevity for the tools. Feed rate calculators, for example, are a fantastic resource and can often be found on both CNC machine manufacturers’ and tool suppliers’ websites. A combination of following manufacturer guidelines and some in-house testing will yield the best results, with the lowest chance of damaging tools.

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