A Collet is a subtype of chuck that forms a collar around an object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar. It may be used to hold a workpiece or a tool.

There are two things you want to avoid when installing a collet, and they are as simple as doing too little and or too much. If you under tighten the collet there is a chance that the tool could be pulled out of the collet whilst cutting.

If you find yourself over tightening, it distorts the collet and diminishes holding strength and accuracy. If you over tighten the collet you risk damaging the cutter and misaligning the tool which will invariably result in a poor-quality finished product, never mind the wasted material and time.

As you tighten the nut, which comes down and contacts the faces of the collet, it creates friction. If you over tighten, that friction wants to twist the top of the collet. Instead of more clamping force, it reduces it because with the over tightening, it then creates gaps in the contact path and introduce more run out. Over tightening can be avoided by using a torque wrench.

Sandvik Coromant’s Gary Godfrey says when operators clamp the nut on the collet, they try to get it really tight, they put a standard wrench on it and hit it with a hammer, or they put a big bar on the wrench and just tighten it as tight as they can.

“The thread that is on the chuck eventually ends up cracking. Torque wrenches are often recommended but are typically considered a spare part, adding cost to the tool, so a lot of shops just don’t buy them,” he said.

When should you replace your collets?

The collet is designed to wear and be replaced. Collets have a life span of 400-600 hours, which roughly translates to between two and three months assuming the collet is used eight hours a day.

Collets can be damaged without any visible signs. The most common problem is metal fatigue. An easy way to see if there is metal fatigue is to insert the tool shank into the back of the collet and then try it in the front side. If the tightness is not the same both ways, then the collet is fatigued and should be discarded.

One major cause of collet metal fatigue is from over tightening. A tool holder tightening stand and torque wrench should always be used.

By replacing your collet as suggested, you ensure your operations run consistently, good cut quality is maintained, and the life of your cutting tools is prolonged.

Remember – collet maintenance!

“Customers only become aware of the collet if their tool life suddenly decreases or run out increases,” said Godfrey.

The loss of clamping pressure is a natural occurrence over time as the collet wears due to the constant heating and cooling during use.

When inspecting your collet, metallic damage, such as bell mouthing or burrs, should be checked with every tool change. If damage is visible, the collet should be discarded and replaced.

When replacing the collet, make sure the flute does not enter the collet, as this will result in run out and can potentially lead to tool breakage.

To ensure proper clamping, the tool shank should fill, at the minimum, 80% of the depth of the collet.

Remember – Cleanliness is King!

Another common problem is not cleaning the collet chuck. The chuck, collet and nut must be thoroughly cleaned before assembly to maintain accuracy. Any dust or dirt around the collet bore affects run out and clamping force.

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AKE Sales Tech has a wide range of products; get in touch with AKE Sales Tech today for wear proof parts for working in all conditions, nesting tools for all the most accurate cutting solutions, bore tools, knife blanks and more. AKE’s application engineers take the greatest of care to ensure the quality of their tools is first class offering customers unique solutions.