Jason Rowe, managing director of CNC World Ltd, talks about how to avoid tool breakages.

Over time, the tool that you use most frequently is going to break. It’s a given. Even the tools that you don’t use that often will reach a point where their function just is not up to scratch anymore. When that day comes, you’ll have no choice but to purchase a new replacement tool. But, until that day? There are ways to ensure that you get the most out of your tools so that you don’t have to even think about buying a new one (at least for a little while!).

Your CNC router is where everything starts; even if you follow the advice on avoiding breakages, if there is a problem with your machine, you still might not achieve a great cut. Look after your machine and check for vibrations. The easiest way to do this is to listen out and feel for any changes and then investigate them.

If the CNC router is where it starts, the tool is the last, and equally important, piece of the puzzle. Tools can be costly, and breakages can cause downtime, so let’s look at why a tool may break and what to look out for.

Cutting edge breakages on your CNC tools

If the tool were to break on the cutting edge it could be for one of three reasons. One, the cutting-edge length could be too long and you’re cutting on the tip of the tool. Two, it’s a feeds and speeds problem – you could be cutting too fast or too slow. Always use a feeds and speeds calculator to ensure the best finish without burning out your tool. Three, the tool is no longer sharp enough and needs replacing.

Shank breakages on your CNC tools

If the tool were to break on the shank, there is most likely a tool holding problem that could be caused by the collet, collet nut or toolholder.


Do you have the right collet for the tool? Sounds simple, but if you have a 6mm tool, use a 6mm collet and not a ¼” (6.35mm) collet with the tool shank at least 85% fully into the collet. If small markings appear on the shank of the tool, it is a sign that the collet is gripping unevenly. This can pinch the tool, affecting the angle that the tool is being held and can reduce the life of both your collets and tools.

It goes for every aspect of your machine but make sure that your collet is clean. Blow an air line over and through the collet or use a collet cleaning brush so that there are no bits of material stuck, as this can affect how it holds the tool.

A rule of thumb is if you’re using the same collet for eight hours a day, five days a week, it would be a good idea to replace them every three to six months, so look out for signs of wear.

Collet nut and holder

The first question to ask is: how old are the collet nut and toolholder? Just like the collets, over time they wear, and this can affect the alignment of the tool. If tools keep breaking in the shank it may be a good time to replace old collet nuts and toolholders.

Preventing breakages not only saves money on buying new tools but on the downtime that results from having to change tools or waiting for new ones to arrive.

With preventing breakages in mind, these are some questions to ask yourself to keep your tools working as well as they should for as long as they should:

  • Is the tool the appropriate length and not cutting on the tip of the tool?
  • Is the tool the correct one for the material being cut?
  • Is the collet filled up so that it grips evenly?
  • Is the collet clean and in good condition?
  • Are the tool holder and collet nut in good condition?
  • Do I have the right feeds and speeds for the tool I’m using?
  • Is there any vibration through the gantry?

If you are still experiencing tool breakages, you should speak to your tooling supplier or book to attend CNC World’s open house on 21st and 22nd September. The company’s team of expert machinists and tooling personnel will be on hand to answer any questions.

Contact the team on 01953 668899 or visit www.cnc-world.co.uk

See the original article as featured in Furniture & Joinery Production Magazine

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