Milling Machines Tool-holding | Shrink Fit vs Collet Chuck ...

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Everybody being it an owner, manager, programmer, or setter who is in-depth into CNC machining is familiar with the fact that the investment, the accuracy, reliability, and precision for a milling or mill turning machine operations is not complete with the sole purchase of the machine itself. Besides the fixtures and work holding devices and the tooling, a great investment and a major factor for the accuracy, ease of use, and reliability of the machining process is the tool holding choice. Today there are many special types of Milling Machines Tool-Holding and tooling solutions to suit best to the intended application. However, the scope of this comparison will be between a few general types which are most commonly used - the collet type, hydraulic, and shrink fit.

Being useful for separate qualities of their own and having their pros and cons, it is very often subject to making a Milling Machines Tool-Holding solution between one of them. However, when deciding which one to use it is their differences that will guide your choice. In order to make a liable comparison, we will try to look at the most important aspects of this decision-making by looking not only at the technical but the economical facts as well.

Precision & Security

We have to start with putting on the scale one of the most important factors. If you think a runout of 0.in could be acceptable you have to read this - studies show that run-outs of 0.in can triple the tool life, meaning that poor precision could be absolutely detrimental and lead to increased tooling costs.

Actually, the three types of tools can show very similar results as far as it concerns accuracy. With radial runouts less than 0.003mm or 0.in achievable with all types, it is out of the question that we can get the desired results. Even some ER types of collets which suffer from pullout stability and torque transmission, are able to deliver 0.002-0.005mm or 0.-0.in. However, there are other collet type holders like the so-called power chucks being far more superior in terms of power. They have features like axial slits to prevent tool rotation and radial ones preventing the tool pull out. The gripping force of these chucks is powerful enough to actually compress the tool shank slightly and expand into the slits. Tests show that the chucking torque force can deliver up to Nm or lbf and this combined with an acceptable radial runout of less than 0.in.

Shrink fit and hydraulic tool holders are offering unsurpassed gripping and high clamping torque and no centrifugal forces due to clamping segments. Depending on the clamping diameter the hydraulic ones can deliver over nm (lbf).

The hydraulic tool holders offer higher holding forces of shrinking, high torque transmission, and bending distance 1.4 times greater than shrink chuck. A big plus is the dampening effect due to the cushioning of the hydraulic membrane. The shrink system on the other side is a bit less reliant in terms of vibration because of its dependence on the heating and cooling processes.

Variativity & Flexibility

When talking about making choices it is of great importance to know the limits and restrictions of the different tool holder types. Generally speaking, the collet chucks are the most versatile ones as they can come in different standards and sizes, different sized collets, and even size ranges for them. They can conduct coolant in a different way just by switching to a different type of collet. As well as with the hydraulic ones that have sleeves they can both use a through coolant channel system for tools without coolant holes to deliver it directly to the cutting edge. On the other side the shrink fit can only use flush or through coolant which makes it a bit more demanding for delivering it well for milling operations.

While considering the accessibility, the collet type chucks cannot offer as good as the shrink fit and the hydraulic solution. The collet chuck is comprised of a collet, holder body, and a cap which is comparatively much bigger than the maximum size of the tool to be clamped. Although an extension can be employed it will compromise both the gripping force and the accuracy.

Actually, the shrink fit tool holders were unsurpassed in terms of accessibility because of their elongated design, a fact which with the advance of 3D metal printing technology changed to a great extent. Now on the market, you have hydraulic systems allowing for deep reach and side clearance comparable to the shrink fit systems.

For more information, please visit Hydraulic Tool Holder Vs Collet.

It must be noted that an important feature to look at while choosing the hydraulic is the position of the membrane as not all tool manufacturers would offer to have it from the front of the holder meaning that for smaller applications the tool will be supported further from the cutting zone. Also, the clamping depth has a minimum before which it is not recommended to use.

Setup & Maintenance

Probably you can guess that the shrink fit is most uncomfortable because of the heating and cooling processes involved. An inconvenience for an operator will not only be the risk of burning but the wait for the cooling before the tool can be used. Hydraulic systems can lock the tool simply by tightening with a hex wrench or a sector key which is the most common case with the collet types too.

Initial Investment

As we already discussed some of the pros and cons technically we should now look at the numbers behind the investment. Being the newest and more advanced technology the hydraulic tool holders have relatively highest prices among all. This is because of the delicate clamping membrane built into the holders which adds cost.

Besides the smaller sized ones that can only clamp a single diameter the reduction sleeves available are about $150 at least. The same is the situation with the power chucks from the collet type holders and only the ER type collets and the ER holder itself or similar could be of low price

Shrink fit holders are of a slightly lower price than the hydraulic chucks. However, the major difference for this type of solution will be the induction heater shrink fit machine which starts at prices around $.

Conclusion

Having exposed all the above it is clear that each and every solution has its advantages over the other two. Being based on the accuracy, price, accessibility, or whatever factor it will be difficult to stick to only one of the tool holder types. Therefore order to get the advantage of the features of the three tool types to offer most. Shops wouldn't use only a single type, but a combination, if not all of them. Which ones you will choose is up to you!

Each tool holder style has its own unique properties that must be considered prior to beginning a machining operation. A secure machine-to-tool connection will result in a more profitable shop, as a poor connection can cause tool runout, pull-out, scrapped parts, damaged tools, and exhausted shop resources. An understanding of tool holders, shank features, and best practices is therefore pivotal for every machinist to know to ensure reliable tool holding.

Types of Tool Holding

The basic concept of any tool holder is to create a compression force around the cutting tool&#;s shank that is strong, secure, and rigid. These come in a variety of styles, each with its own spindle interface, taper for clearance, and compression force methods.

Mechanical Spindle Tightening

The most basic way in which spindle compression is generated is by simple mechanical tightening of the holder itself, or a collet within the holder. The downside of this mechanical tightening method of the spindle is its limited number of pressure points. With this style, segments of a collet collapse around the shank, and there is no uniform, concentric force holding the tool around its full circumference.

Hydraulic Tool Holders

Other methods create a more concentric pressure, gripping the tool&#;s shank over a larger surface area. Hydraulic tool holders create this scenario. They are tightened via a pressurized fluid inside the bore of the holder, creating a more powerful clamping force on the shank.

Shrink Fit Tool Holders

Shrink fit tool holders are another high quality tool holding mechanism. This method works by using the thermal properties of the device to expand its opening slightly larger than the shank of the tool. The tool is placed inside the holder, after which the holder is allowed to cool, contracting down close to its original size and creating a tremendous compressive force around the shank. Since the expansion of the bore in the tool holder is minuscule, a tight tolerance is needed on the shank to ensure it can fit every time. Shank diameters with h6 tolerances ensure the tool will always work properly and reliably with a shrink fit holder.

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Types of Shank Modifications

Along with choosing correctly when it comes to tool holding options, tool shanks can be modified to promote a more secure machine-to-tool connection. These modifications can include added grooves on the shank, flats, or even an altered shank surface to aid in gripping strength.

Weldon Flats

A Weldon flat can be used to create additional strength within the tool holder. The tool holder locks a tool in place with a set screw pushing on a flat area on the tool shank. Weldon flats offer a good amount of pull-out prevention due to the set screw sitting in the recessed shank flat. Often seen as an outdated method of tool holding, this method is most effective for larger, stronger tools where runout is less of a concern.

ToughGRIP Shanks

Helical Solutions offers a ToughGRIP shank modification to its customers, which works by increasing the friction of the shank &#; making it easier to grip for the tool holder. This modification roughs the shank&#;s surface while maintaining h6 shrink fit tolerance.

Haimer Safe-Lock&#;

In the Haimer Safe-Lock system, special drive keys in the chuck interface with grooves in the shank of the tool to prevent pull-out. The end mill effectively screws into the tool holder, which causes a connection that only becomes more secure as the tool is running. Haimer Safe-Lock&#; maintains h6 shank tolerances, ensuring an even tighter connection with shrink fit holders.

Key Takeaways

While choosing a proper cutter and running it at appropriate running parameters are key factors to a machining operation, so too is the method used. If opting for an improper tool holding method, one can experience tool pull-out, tool runout, and scrapped jobs. Effective tool holding will prevent premature tool failure and allow machinists to feel confident while pushing the tool to its full potential.

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Harvey Performance Company&#;s team of engineers works together to ensure that your every machining challenge &#; from tool selection and application support to designing the perfect custom tool for your next job &#; is rectified with a thoughtful, comprehensive solution.

Contact us to discuss your requirements of Chuck Vs Collet. Our experienced sales team can help you identify the options that best suit your needs.