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CNC Router Essentials

3 : Toolpath Essentials

rather than liing it, which can occur with an upcut bit. Because a downcut bit pushes the chips down when cuing, the chips usually get packed into the kerf. The packed-in chips will fall away when you separate the finished parts. If you need to remove them before that, try running the cut a second time to loosen up the chips and then remove them with compressed air or a vacuum.

Compression bits combine upcut and downcut shearing action in one bit and thus leave a clean cut on both the top and boom side of your material.

Router bits

Many of the bits you use with your handheld router or router table can be used in your CNC. There are also specialized bits for CNC that you will find useful. Carbide-tipped or solid carbide bits are the most commonly used bits on CNC routers because they stand up to abrasive materials such as MDF and plywood. However, due to their hardness, they are also more susceptible to breakage than high-speed steel (HSS). HSS also has the advantage of being less expensive than carbide, although HSS bits generally dull quicker.

You probably already own a few straight bits. These are good general purpose bits, but won’t give you the cut quality of a spiral bit. Spiral bits are available as upcut, downcut, or a combination, Image 3.1. Upcut bits act like a drill bit, pulling chips up out of the cut, which keeps the cuing path clear. The spiral creates a shearing action that reduces chipping and gives you a beer edge quality on your material than a straight fluted bit. An upcut bit may fray or chip the top surface of your material, but when through cuing, it provides a chip-free cut on the boom side.

Downcut spiral bits push down toward the material. This downward shear action provides chip-free cuing on the top surface but may cause chipping on the boom of some materials, such as melamine and plywood. Downcut spiral bits are also useful when cuing thin materials because the downcut pressure helps to hold the material against the bed

A router bit starter set

Image 3.1: Straight bits come in a variety of configurations. The four shown here are (left to right): straight flute, upcut spiral end mill, downcut spiral end mill, and compression end mill.

• 60 and 90° V-bits (V-carving) • "-, "-, and "-diameter upcut spiral straight bits (general cutting)

• " ballnose bit (3-D finish carving)