When choosing a CNC router bit, a person must have an understanding of the way in which each type of CNC router bit interacts with the materials that is being cut. A person must choose a CNC router bit according to the specific task that the CNC router machine must perform, as each type of CNC router bit will produce different results in the material that is being cut. Upcut spiral bits are manufactured in ways that enable the bits to pull the chips out of the cut, and keep the bottom edge of the cut clean.
However, when using upcut spiral bits, the top edge of the cut can begin to tear out. Thus, a person can use downcut spiral bits instead, as they will push the material downward to protect the visible face of the work piece. However, downcut spiral bits do not clear chips as well as upcut spiral bits.
How to Choose the Right CNC Router Bit
Compression spiral bits are manufactured with the features of both upcut and downcut spiral bits, and are used in scenarios where laminated sheet goods is being cut or where fragile surface layers of the material are to be cut. Bits with ball nose features smooth curves to the bits instead of the sharp corners that other bits create. Ball nose bits are used in scenarios where the CNC router machine is to cut an organic shape in the material.
V-bits are used for lettering and decorative grooves, as the width of the cut that V-bits make changes as the bit goes deeper into the material. Straight bits are used in situations where the CNC router machine will need to create a square shoulder or a flat bottom to a cut piece of the material. The flute count of the CNC router bit is another important variable in the selection of which CNC router bits to use.
For example, a single flute CNC router bit will clear chips out of the material more aggressive, and will produce less heat for cutting soft plastics or foam. Two flute and three flute CNC router bits will produce a smoother cut on hardwoods. Bits that have more flutes require higher feed rates to ensure that the flutes do not begin to rub against the material during cutting, which could produce heat for the CNC router bit.
A larger shank diameter will provide more rigidity to the CNC router bit than those with smaller shank diameters. For example, a CNC router bit with a half-inch shank will be more rigid than one with a quarter-inch shank. Thus, large CNC router bits will have a half inch shank.
Smaller shanks can be used for detail work, but will limit the speed at which the CNC router bit can move through the material before it begins to create runout in the CNC router bit’s cut. The material that is to be cut must be matched with the CNC router bit that will be used to cut that material. Materials like hardwoods require the CNC router bit to have sharp carbide edges, as anything less may cause the wood to burn.
Materials like aluminum require polished flute edges with specific coatings to prevent the aluminum chips from adhering to the CNC router bit. Finally, plastics can melt when heat is built up in the plastic, so higher feed rates and lower RPM settings are used for plastic materials. Another important component of CNC router bits are the collets.
Collets can wear over time, and become dirty. If the collet wears or becomes dirty, this will introduce runout into the CNC router bit. Runout caused by a bad collet will shorten the life of the CNC router bit, and will ruin the finish of the material that is being cut.
Thus, a person must ensure that the collet is matched to the CNC router machine’s spindle, and must replace the collet according to a set schedule. Many people makes mistakes with CNC router bits. For instance, if the CNC router machine is set to run the CNC router bit too slowly, the bits will rub against the material, creating heat that will dull the CNC router bit faster then if the bit was performing a chip load.
If the CNC router bit is inserted deep enough into the material, the machine will not grip the CNC router bit properly, causing the bit to vibrate or pull out of the material. Although climb milling is often thought to be smoother when cutting metals, conventional milling is a safer option for cutting wood parts. A person can determine if the CNC router bit settings are correct by inspecting the chips that are cut out of the material, as well as the edges of the material.
If the chips are clean, the edges are smooth, and there are no burn marks along the edges of the cut, then the settings for the CNC router bit are correct. If there are any burn marks, chattering of the material, or torn fibers in the material, the settings for the CNC router bit need to be adjusted.
