How to extend the life of you cutting tools
The life of your cutting tools depends on the care and consideration you take with them. Checking and changing tool holders and collets when needed can drastically increase the life of your cutting tools. Many of the new CNC machines have the ability to automatically change the tool holders in the spindle as needed. Even if this process is automated, it is still important to check the tool holders for wear and replace them as needed to prevent premature cutting tool failure, poor cutting performance, or even expensive damage to the spindle.
There are four main parts to a tool holder (also called collet holder or collet chuck).
- Pull Stud– The pull stud screws into the top of the taper of the tool holder. The pull stud is held by the clamping set inside the spindle which pulls the holder up into the mouth of the spindle. A spring-loaded draw bar is used to pull the holder into place. Some Pull studs are hollow to allow coolant to flow through the tool holder.
- The Taper- the taper is the conical shaped area of the tool holder that goes into the spindle when changing the tool. An 8 degree taper automatically centers the tool into the spindle. The taper on all our tool holders is ground to a tolerance of .0002” for both the taper tolerance and the outside diameter tolerance. Our HSK tool holders have a shorter taper than our BT style.
- V-Flange- The V-Flange is usually identified as the “V” groove found on the outer most diameter of the tool holder. The automatic tool changer locks onto the V-Flange on the tool holder when moving the tool from the tool changer to the spindle and back. The cutouts in the flange help align and adjust the holder in the spindle.
- Collet Pocket- The collet pocket is the part of the tool holder where the collet is placed into before the collet nut secures it.
The cutting tool is held by the collet. The collet is designed to collapse around the shank of the cutting tool when pressure from the collet nut is applied. As the nut is tightened, the collet is tightened around the cutting tool, pushing it deeper into the collet pocket until maximum pressure is achieved. For a guide on how tight the collet should be, checkout our article on “How to get proper tightness for your collets.”
One of the first things to check on your tool holders is the spindle mouth. A worn spindle mouth (sometimes called bell mouthing) can cause runout issues that can affect the accuracy of the tool holder and can cause bad cut quality and reduce efficiency. You can see if bell mouthing is the cause of the issues by checking to see if the tool holder issues are eliminated by bench checking the TIR. If they are, then the problem is most likely a worn out spindle mouth.
Make sure the ATC IS properly aligned. If the ATC swing arm is not in alignment, then it will not insert the tool holder perfectly. This can cause damage to the spindle and tool holder, and reduce the life of your cutting tools.
Over time, the taper can become worn or damaged. You should check the taper for signs of wear, especially where the taper contacts the spindle mouth. Issues with the taper directly affect the accuracy of the machining. If there are any issues with the taper or if there is fretting, the tool holder must be replaced. Fretting occurs when two steel parts (like the tool holder and spindle mouth) are rubbing against one another. Fretting is caused by the tool holder taper and the spindle not being aligned perfectly and creating vibration and heat, which then develops into fretting. You can tell if there is fretting by the brownish, copper colored marks that are often mistaken for rust.
If a new tool holder is showing evidence of fretting, or if the tool holder is sticking in the spindle, this may indicate that the spindle needs to be reground. When the taper on a tool holder is worn, it can cause an out-of-round condition when the tool holder is inserted into the spindle called runout. Runout can be responsible for prematurely wearing out your cutting tools and can also cause a lot of vibration resulting in bad surface finish. The vibration caused from runout can also create heat build-up in the spindle and damage the spindle bearings.
Don’t forget your collets
Collets are made from a softer metal and have slots and cut outs that allow them to collapse and spring so that they grip the cutting tools tightly. The constant collapsing and springing to adjust and tightly grip the cutting tools caused the collets to wear out more quickly than the tool holder. Using a worn out collet can cause the tools and tool holders to prematurely fail. These tools and tool holders can be very expensive to replace. Changing the collets regularly and as needed can save thousands of dollars in tooling costs. Scoring marks on the inside diameter may indicate that the cutting tool was spinning inside the collet and are good indication that the collet needs to be replaced. You should also replace collets if they have any rust or pit. You should wipe down the tool holders and spray a light coating of rust preventative when they are not going to be used to help lengthen the life of the tool holder and collets. When it is time to use the tool holder again, be sure to wipe the oil off completely before placing it back in to the spindle. Using the correct coolant concentration can also help prevent rust on the collets and tool holders.
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