A CNC is only as good as the bits that you use. If you don’t know which CNC bit to use, your projects won’t turn out as good as you would have hoped. There are a lot of creative possibilities when using a CNC machine, from beautiful wooden designs to cutting glass or other materials.
We’re going to be looking at what different CNC bits are used for different projects so that you have a firm understanding of your full capabilities with the bits you have available.
What Different CNC Bits are Used for
Bits typically fall into one of two categories: drill or milling bits. While it may sound like there are only two options, there are a lot of variables with each bit that also needs to be looked at and examined first.
What are Drill Bits?
A drill bit goes into materials completely. For example, these are the bits that are used for making holes for screws or other fasteners to attach.
What are Milling Bits?
If you want to make designs and patterns, milling bits are what you’ll want to use. These bits cut laterally, across materials, to help create 3D designs. A few of the different names that these bits go by include:
- Carving bits
- End mills
These are the bits you’ll want to use to create any patterns or designs in your work.
Understanding CNC Bit Terminology
A lot of terminology is used when learning about bits and the different variables that they include. It’s important to understand some of this jargon so that you can identify the difference in bit characteristics:
Flutes add to the strength of the bit and directly correlate to the feed rate. You can feed through materials faster when more flutes are present without concern of burning. Fewer flutes means that a slower feed rate is required, as more material is removed.
- Straight flute – Ideal for wood and plastic, these flutes don’t extract the material when used. This flute offers a nice, clean finish and is more affordable.
- Spiral flute – A flute with a helix that removes material. These flutes are good for aluminum, plastic and wood.
Feed rates are often measured in feet per minute or IPM. This is a measurement of the bit’s movement speed laterally through the material you’re using.
RPM, or revolutions per minute, are what people talk about when discussing speed.
You’ll also see something called “chip load.” A chip load is the size of the pieces removed from the material when the drill bit enters the material. For example, when the drill bit enters wood, some wood is removed with every revolution of the bit.
Small chips may sound beneficial at first, but since they’re not removed rapidly, they can generate more heat, which can cause the bit to fail due to poor heat transfer.
You’ll want to consider all of this when using a CNC machine because what different CNC bits are used for will depend on a lot of these factors outlined above.
CNC Bits and the Materials Used for Different Bits
Bits are made out of a variety of materials. Some bits are cheaper in price, so they’ll be made from cheaper materials. While there’s always room for cheaper bits, it’s often best to choose the right bit material for the job you’re doing.
The most common materials used for CNC bits are:
- Carbide. A common bit material with a steel body and carbide tip that increases the longevity of the bit at a lower cost than the solid tungsten carbide.
- HSS. The high-speed steel bits have a higher hardness, heat resistance and wear resistance, making them a good option for cutting. The one downside is that the lifespan is shorter compared to its carbide counterparts.
- PCD. A highly durable bit that is made from polycrystalline diamond. The blend of carbide and diamond make this bit extremely hard and resistant to abrasion.
- SC. Known for being sturdy, solid carbide bits are wear-resistant and durable, albeit they can be brittle. It’s important to do your due diligence when choosing these bits because there are a lot of knock-off items being sold that will break faster.
- Solid Tungsten Carbide. Expensive yet durable, these bits mix metallic cobalt and tungsten carbide together to offer a long-lasting sharpness, extreme durability and a sturdy final product.
The material you use needs to have the right bit because the most common materials have their drawbacks. A few of the issues that are present with different materials are:
- Aluminum requires bits that won’t cause fusing or rewelding due to excessive heat.
- Hardwood requires bits that provide clean edges.
- Plastics are susceptible to melting and will require a bit that won’t cause melting or excessive heat.
- Plywood is less durable, so the bit shouldn’t cause any mangling of the wood.
Want to buy a decent, all-purpose bit? Try to find the 2-flute up cutting spiral bit. This bit is a great bit for most uses, although the material you plan on drilling into will play a role in the bit used.
Choosing a Bit Based on Flute and Bit Cut Direction
A bit has a lot of characteristics, outlined previously, and this will factor into your choice for the right bit. The bit cut direction is one of the most important. The following exist:
An up cut is used when trying to prevent overheating because it clears chips away. This is the most common cut and is used for clean cuts through materials.
Ideal for working with thinner materials. The down cut will press the material back into the cut and will preserve the top layer of the material. If you don’t want to drill through the bottom layer, this cut works well. Otherwise, it’s not recommended to cut through the bottom layer because it will cause fraying.
Not sure which cut direction to choose? Compression is the best. The compression cut has a down cut with a tip that’s an up cut. These bits provide clean edges on both sides, but if you want to make holes, do not use this bit.
When flutes are chosen, a general rule of thumb is that a single flute will have rougher edges than multiple flutes. The higher the flutes, the slower the drilling process. One flute allows for rapid speeds and greater chip clearance than, say, a four flute option would allow.
Extending the Life of Your Bits
You should store your bits properly to extend their lifespan. A few of the key tips here are:
- Don’t allow your bits to bang together to avoid potential damage
- Carbide bits are brittle and can be damaged easier
- Try to separate bits and cover them with a lid
It seems simple enough, but a lot of people simply throw their bits into a bin, causing them to lose their edges much faster than if they were properly stored. A little extra time thinking about storage can go a long way in ensuring that your bits last longer.
Now that you know which CNC bit to use, you’ll have an easier time on your next project and also be on your way to having longer-lasting bits.
P.S. It’s also not uncommon to have a lot of different bits to allow for flexibility over time. Some bits are interchangeable with other machines you might own – check if you can use your bits with a router.