Category: Maintenance

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Why are my CNC bits breaking?

Why Your CNC Bits Are Breaking

Every so often, I’m asked the question “Why are my CNC bits breaking?” and then the process of elimination begins. There are an array of issues that could be causing this to happen. Here are the most common:

  1. Incorrect feed/speed
  2. Dull bit
  3. Bad vacuum/hold-down
  4. Debris in collet/tool holder
  5. Bad collet

Incorrect Feed Rate & Spindle Speed

First off, the feed rate and spindle speed are often the culprit. Bits can break at too high or too low of both the feed rate and spindle speed. It’s important to find the correct mix of feeds/speeds that meets your material and quality requirements. The easiest solution for this is to send an email to tooling@cnctoolingshop.com. On a daily basis, I’m troubleshooting and offering starting points on how to cut a specific material for my customers.

Dull Bit

Most operators know this, but a dull CNC bit is far more likely to break than a new sharp one. Instead of the dull bit cutting through the material, the pressure is pushing through it until it no longer can. In this case, a smaller diameter tool will break before a larger one will. Pay attention to the cut quality and sound coming from the tool when a new tool is cutting vs. a used one. This way you can spot a dull tool before it breaks or sacrifices too much quality.

Poor Vacuum/Hold-Down

Bad material hold-down can very easily break a bit. Vibration or material movement is the enemy. The hold-down could be bad because of vacuum problems or even a vacuum not suitable for your machine, lack of milling the spoil board, vacuum pressure leaking out the side of material, etc. Do whatever you have to do to keep material held in place. Some people use double-sided tape, down-spiral bits, vacuum cups, or vacuum enhancers to further decrease movement. Again, do everything in your power to keep material held in place.

Debris In Collet/Tool Holder

If tool holders and collets are not properly cleaned, debris can build up and cause the tool holder to be off balance. When your CNC machine is cutting material out of balance, you face a decrease in tool life, spindle life, and cut quality. This can easily be a reason why your bits are breaking. Remember that collets and tools holders are consumables and should be replaced in a reasonable time-frame. See a recent article, I wrote, with more detail on tooling maintenance HERE.

Bad Collet

Like I mentioned above, collets are consumables. Depending on use, collets have a 90 day life. When you break a bit near the collet, they should also be replaced because they can damage the collet to where it no longer holds a bit correctly. Think of a collet as a spring. If a spring is compacted together for 90 straight days, it will no longer be the spring it once was. Therefore, your CNC bits are not being held as tight and balanced as they need to be. Find collets on our webstore HERE

Greg Smolka

Greg Smolka (Author)

CNC Tooling & Application Manager

Here to help with tooling recommendations (bits, knives, collets, tool holders, maintenance kits, torque stations, etc.) and cutting recommendations (feeds/speeds, tips/tricks, # of passes, etc.).

Contact Info: greg@cnctoolingshop.com

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CNC Tool Holder & Collet Maintenance

CNC Tool Holder And Collet Maintenance

Taking proper care of your collets and tool holders will not only increase the life of your collets and tool holders but it will also increase the life of your CNC router bits and spindle. This will in turn improve cut quality and performance. I like to think of tooling maintenance like changing the oil in a car. Sure, the car will run (for a while) without changing the oil. However, there is a risk of blowing a gasket and warping other parts of the engine until it ultimately fails. The same goes for a CNC router. The more time a spindle is in use while being out of balance, the more of a chance it risks failing. For those of you who want to get the best out of your CNC machine investment, let’s discuss tooling maintenance.

Did you know that both the collet and tool holder have a life cycle? Collets should be replaced after roughly three months. They can be damaged or compromised without any visible signs. A very common problem is metal fatigue which can be caused from overtightening and/or cutting pressure. Be sure to use a torque wrench and tightening stand to escape this problem.

Regardless, over time the gripping power will reduce with use and heat. This is why it’s very important to replace these in a timely manner. Tool holders, on the other hand, have a much longer life cycle. They should be replaced every one to two years. Like the collets, these will break down over time. Fretting and bronzing are common as tool holders get older. This is all of course dependent on the use of these tools. If a collet and tool holder is only used for an hour a week, then yes it may last longer. However, that’s if the collet is removed from the tool holder and both are cleaned and kept in a dust-free area. I have a habit of cleaning my tools after every use then putting them back in the original packaging. Not every operator has this luxury because of time constraints. So, for most of you, replacing them in a timely manner, even if they aren’t used as often, is the best option.

Besides replacing these parts when needed, It’s also important to take care of them while in use. Proper cleaning is essential for reaching full life cycles of each and achieving best cutting results. Here are the cleaning steps that should be done on a regular basis. This should be done every time a tool is changed or replaced from a collet/tool-holder.

Step 1

Use air to blow off as much from the tool holder and collet as possible. Blow off any debris, dust, and material chips. Build up often happens within the gaps of the collet. Not blowing these out could cause the collet from not being able to tighten properly.

Step 2

Use a clothe rag or paper towel to wipe off any leftover dust or material chips that are stuck to the collet and tool holder. Sometimes using a folded piece of paper will help get hard to reach chips lodged in the collet gaps.

Step 3

Use the Spindle Wiper Kit to clean out the spindle opening, tool holder opening and center of collet. These are made to clean the hard to reach areas. This is especially important in the spindle and collet opening because they are nearly impossible to clean without this kit.

Step 4

Use the Nu-Tool Cleaning Protectant & Rust/Debris Remover to thoroughly clean the collet and tool holder. The rust/debris remover is only needed when rust or heavy debris are present on your tooling. For the most part, the protectant is the go-to product. This should be used to aid in cleaning every time a CNC bit is replaced. At the minimum, these should be cleaned weekly to get the most out of your tooling.

If these steps are regularly taken, you will get the most out of your collets and tool holders. Your cut quality will be the best that it can be and your spindle will be in balance which in turn will allow it to last longer. Again, treating your machine like you would a car by giving it regular maintenance will help you get the most out of your CNC machine investment.

If you have any questions about this process, the products, or would like me to examine your tooling, please email me at greg@cnctoolingshop.com or call me at (616) 502-7277.

Greg Smolka

Greg Smolka (Author)

CNC Tooling & Application Manager

Here to help with tooling recommendations (bits, knives, collets, tool holders, maintenance kits, torque stations, etc.) and cutting recommendations (feeds/speeds, tips/tricks, # of passes, etc.).

Contact Info: greg@cnctoolingshop.com