Picture of a CNC router bit.

What you need to know to make your CNC bits last?

Understanding these concepts will extend the life of your bit and make your projects better.

There are several things I try to avoid when using my CNC bits, with the most obvious being, “don’t run your bit into anything!” But, beyond that things are less obvious. If you like what you are reading, please “like” and follow below.

1. Improper Speed.

Determining your proper speed or Revolutions Per Minute can be a bit dicey, but the good news is from my experience you do have a decent amount of leeway. My first suggestion is to go to your router or spindles specifications information. I run the Makita RT701C so I know what the numbers on the dial actually refer to. The next step is going and researching the specific bit you are using information. I know for my favorite bit, the manufacturer suggest 17,000 rpm.

Can you tell if the speed isn’t working? Of course. Many times if your speed is too fast you will get burn marks and a high pitch squealing sound. Too slow, it sounds like it is bogging down or struggling and edges that should be smooth look choppy. You can also tell some, and this is where feed rate comes in, by the size of the chip out. The particles coming off your project (generally speaking) should be about the size of a sesame seed.

2. Running the Wrong Feed Rate

So this one is tricky. Figuring out your feed rate is difficult in the beginning and ultimately it comes down to experience. I use a the manufacturers feed rate chart to get in the right ball park and then tune it with experience. Most website information I have seen is to slow. I bump up almost all of my feed rates vs. what the manufacturer says.

Again, this is where you want to look for the chip out (pieces that are being cut off your project). If you are getting dust, you are not challenging the bit- and you want that.

3. Using Traditional Roughing


Diagram describes the difference between high efficiency milling and traditional.


This one is complicated but it ultimately will run down to what software you are using to program. With Fusion 360 you have options within the CAM to change the way you do your roughing passes. SpeTools says, “While traditional roughing is occasionally necessary or optimal, it is generally inferior to High Efficiency Milling (HEM). HEM is a roughing technique that uses a lower Radial Depth of Cut (RDOC) and a higher Axial Depth of Cut (ADOC). This spreads wear evenly across the cutting edge, dissipates heat, and reduces the chance of tool failure.”

4. Improper Tool Mount

I think this is a no brainer, but if your shank isn’t properly fitted in the collar, it will reduce the life of your bit. Just like the loose drill bit causes damage to the side of the bit, it happens moreso with CNC due to the horizontal pressures being applied.

Every machine is different, but what I do is remove the previous bit and tap out the dust that inevitably makes it in the collar. If it seems bad or I know I have done several hard cuts I remove the collar and clean all that out. I then replace the bit and tighten the collar with the wrenches that came with my router. I say that because a larger wrench will give you more torque and can damage the tool causing fracture. Fracture… Is bad.

5. Not using a Variable Helix/Pitch Geometry Bit

Ok, this one is easy. Don’t buy garbage bits or use drill bits!!!


Image shows an example of Variable Helix/Pitch Geometry.


What this is referring to is that your bit is not actually perfectly symmetrical on the axis al the way down. The angles (see picture) of a and b are just a bit different. And you are like, why? It has to do with reducing harmonics. If your bit starts creating those harmonics the vibration increases which in-turn causes bit ware.

6. Improper or less effective Coating

This one is a refer to the manual question. Bottom line, a bit that is coated one way will cut wood properly due to it’s resistance to ware, but fail faster when cutting aluminum. Same hold true the opposite way. The increase in hardness and abrasion resistance that is great for metal, does not work optimally for wood.

7. Wrong Bit Length of Cut

On this topic SpeTools says, “For some jobs, long length of cut is necessary, especially in finishing operation. As a general rule, a tool’s LOC should be only as long as needed to ensure that the tool retains as much of its original substrate as possible. The longer a tool’s LOC the more susceptible to deflection it becomes, in turn decreasing its effective tool life and increasing the chance of fracture.”

8. Wrong Flute Count


This image shows different numbers of flute counts available for bits.


Again, I’m not a scientist so I am going to share the information SpeTools has about this subject. Bottom line is to go with the tools recommended use for what you are doing.

As most people think, high flute counts are always better than lower counts. Lower flute count (2 to 3) has larger flute valleys and smaller bit core, while the higher count flute (5 or above) bit is opposite. But it depends. Lower flute counts are typically used in aluminum and non-ferrous materials, partly because the softness of these materials allows more flexibility for increased metal removal rates, but also because of the properties of their chips. Non-ferrous materials usually produce longer, stringier chips and a lower flute count helps reduce chip recutting. Higher flute count tools are usually necessary for harder ferrous materials, both for their increased strength and because chip recutting is less of a concern since these materials often produce much smaller chips. (via spetools.com)


Hope that helps, and please like/follow below!

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Have a great one!


Hill Country CNC & Woodwork

I hope you like my content and I mostly do this just because I love woodworking, CNCs, Graphic Design, Web Design and Blogging, but I do try to make ends meet with things like affiliate marketing. For me it’s mostly about getting my name out their, any help is truly appreciated!

#cnc #cncmachining #makersgonnamake

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