The importance of accurate toolholding
Toolholding, whose significance is often overlooked plays a very important, critical part in connecting the machine spindle and cutting tool. When the CNC set-up is not coupled with clean, accurate parts & accessories, it can have problematic if not disastrous results causing significant production downtime and costly rework.
Quality toolholding represents a small investment that can make an enormous difference to productivity cost saving and profit.
If there are ongoing problems with noise or finish and you have replaced collets and collet nut without improvement, then you need to replace the toolholder. Toolholders are under considerable tension and pressure when cutting and temperature fluctuations can be up to 60°C. This can cause them to warp, and the cutting tool loses its accuracy and concentricity. Finish is inferior, noise and machine vibration are increased.
The two main areas of wear are:
- The tapers. When the taper on the toolholder wears, they cease to sit perfectly with the matching taper in the spindle of the CNC. Their grip is no longer concentric and power transmission is compromised.
- The collet nut. When collet nuts become distorted and the threads worn, the collet ceases to be evenly and concentrically held in the tool holder.
Using a top-quality toolholder is essential to protect the investment of high-quality machines, spindles and cutting tools. With ever-higher speeds and feeds, toolholder quality and balance has never been more critical.
This is the essential piece of equipment that is gripping the cutting tool. If the collet is not performing, your cutter isn’t either! The collet may be dirty, worn or damaged. Collets are recommended to be replaced every 400-600 working hours.
So how do you tell if the collet is worn or damaged?
The hardest to detect is if your collet is just plain worn-out. The spring steel gets worn from the tightening & untightening and gets fatigued by temperature fluctuations while in use. Collets are recommended to be replaced every 400-600 working hours, thats every 3-4 months if used 8 hours a day. If you are unsure of the hours, one way to check it accuracy is to insert the shank of the cutter into one end of the collet, there should be a slight resistance. Take it out and try the same with the other end of the collet. The resistance should be the same. If this is not the case, the collet should be replaced. Another thing to look for - are there marks on the cutter where it has been gripped by the collet? If there are visible marks, that means that the collet is dirty and needs to be replaced.
Also, check for physical damage such as any burrs and damage to the inside & outside of the collet. This is very important as the tapers of the collets and toolholders need match perfectly. All these affect the concentricity and the grip of the collet and can cause far more damage in a very short time than the cost of the new collet. A collet needs to be replaced if a tool has broken inside the collet.
One way to preserve the life and accuracy is to keep your collets clean. Soak them overnight in our non toxic, non volatile Gleiten Clean, then clean the hole up the center of the collet with the correct size brass collet brush to remove dissolved resin and dirt. Wipe the outside clean.
Maintenance is the key - watch our instructional video on how to look after your collets.
3. Collet nuts and torque spanner
The correct tightness is critical. Incorrect tightening wears collet nuts out faster. With continuous tightening/loosing they become distorted and their threads become worn causing them to lose their essential concentricity.
Overtightening actually reduces the total clamping force. Overtightening can disort the collets so much that it becomes as dangerous as not tightening it enough. We see this a lot. An overtightened collet nut and collet are forced to grip extremely tightly at the bottom of the toolholder which puts extreme and uneven pressure at one small area on the shank of the cutter, which will eventually cause the cutter to break as it is not being held securely over the full length of the shank. It puts excessive, uneven strain on your tool holder, it shortens the useful life of the toolholder, your collet, the tool shank itself, even those super expensive CNC spindle bearings.
Under tightening leads to the tool slippage during cutter operation which is very dangerous and can cause expensive collateral damage and vibration which leads to poor product finish, excess noise and increased tool wear.
4. Loading Tools Correctly
Always insert the collet into the nut first before loading a tool into the collet. This is done by pushing the collet into the collet nut around in a circular motion until it clicks into place.
Then start threading the collet nut onto the toolholder being careful not to cross-thread it. Once it is mostly on, you'll notice that the thread changes slightly. At this point where is changes, this is the point to you to insert your cutting tool to the correct depth in the collet (ideally 80% of the collet needs to be filled). When you start winding the collet nut further on, this it when it starts gripping the shank of the tool securely. Do not let the collet grip onto the flutes of the cutter. The collets must grip onto the shank only.