Understanding these two key bits can really help you start or move forward with your CNC dreams.
We all have our preferences and ultimately it has to do with the job you are working on. I use a Onefinity CNC that runs a Makita router with a 1/4 inch collet. With than said I have found almost no limitations in using a 1/4 up or downcut bit.
Up Cut Bits
Upcut spiral bits are the most popular type of spiral fluted tool. Use these for grooving or slotting, for upward chip evacuation and best finish on the bottom side of the part. These bits allow for rapid cuts since the tool clears the chips away from the material. While ideal for cutting thicker materials, this type of tool is not recommended for thinner or softer materials. When working with these types of material, the upward force can pull the material causing a ragged finish on the top surface, or even worse, eject the part from the table. This type of geometry is used whenever the best finish is needed on the bottom side of a part. (from SpeTools)
What does this mean??? Up Cuts are for removing material. Cutting all the way through a board or removing alot of material like when making a bowl, up cuts are perfect for this in a roughing since.
Down Cut Bits
Downcut spiral bits are best used for thinner materials that will be pushed down into the machine bed rather than being lifted with an up-cut spiral. This can be particularly useful when using vacuum hold down where maintaining the seal between the material and sacrificial bed is crucial. These tools are predominantly used when a high-quality cut finish is required on the top surface of cut parts. Downward spiral tools often require reduced cutting speeds because the chips are pushed back into the material. The chip extraction is generally less effective with this type of tool than it is with an upcut spiral tool. Downcut spiral tools should be used when processing thin materials, 1/8” (3.175mm) or thinner. (from SpeTools)
Down Cuts are my work horse. I use them for everything! With the down cut bit, you get less material removal and a higher surface temperature, but the cuts are crisp and nice. The surface that you are cutting is smooth. Like I said I use this for everything, and yes I am bias! Flags, signs, hardwoods, mdf, you name it.
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Hill Country CNC & Woodwork
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