IBAG North America

7 Most Commonly Asked High Speed Spindle Questions

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1. How Fast Can a High Speed Spindle Go?
High speed spindle speeds can exceed 100,000 RPM, although 30,000 RPM is more common. The maximum speed a spindle can go is determined by several factors, including tooling size and power of the motor. Ultimately, it all comes down to bearing diameter. Small bearings can run faster. Large bearings run slower. Small bearings have limited power. Large bearings can support heavier cuts. Other variables, such as bearing lubrication method and pre-loading, also affect the top speed. So, the tooling system and motor power you choose will usually dictate a bearing size and speed limits. 
2. How Long Will My Spindle Last?
We often hear statements such as, “Why do high speed spindles seem to require service so often? My standard 10K spindle worked for years!” High speed spindles are designed to operate up to a maximum RPM and provide a certain level of power for a reasonable amount of time. Every bearing has a useful life equation. Rotational speed and loading (axial and radial) wear out the bearings. Higher speeds wear them out faster. Proper maintenance, using correct cutting parameters and minimizing vibration due to imbalance will optimize spindle life. In most cases, a typical high speed spindle will operate for an average of 6000 hours before a rebuild is required. Overloading, crashes and operating without proper cooling and lubrication can greatly reduce spindle life. High speed spindles are expensive. More care and preventive maintenance are required to extend the life of a spindle. 
3. Should I Be Using High Speed to Make My Parts?
The maximum RPM you should be running is based upon the material you are trying to cut. The cutter diameter, type of cutting tool you are using (HSS, carbide, coatings) and the material you are cutting all factor into the equation. Every part material has a maximum surface cutting speed recommendation from the cutter manufacturers. This value is based upon the physics of cutting: friction and heat created between your cutter and part material as the cutter removes material (drills or mills) from the part. Running too slow will waste productive time. Running too fast will greatly reduce cutter life. A good balance will yield the best results: more good parts faster.
4. Do My Tools Really Need to Be Balanced?
Imbalance can impose damaging levels of vibration on a spindle. And, to make matters worse, the level of vibration force increases with the square of the RPM. Things go from bad to worse pretty quickly. For low speed spindles, under 10KRPM, vibration forces may not be severe. However, for high speed spindles, excessive vibration can cause poor surface finish, rapid tool wear and spindle bearing damage. So, yes, if you are using a spindle running at more than 10K you must check the balance of your tooling. Use a tooling system that can be balanced (there are many) and make sure you balance to a minimum level, according to the ISO standard DIN ISO 1940-1, of G2.5. This will result in better parts, longer tool life and a healthy spindle.

5. What Are The Best Applications for High Speed Spindles? 
There are many applications that are well suited for high speed spindles. They are ideal for any milling or drilling with very small diameters on any material. A small tool only reaches peak SFPM when run at high RPM. This allows the most productive feeds and speeds. Like small, ball nose end mills for hard steel mold finishing. Also, all soft material cutting (think aluminum, plastics and composites) can utilize very high RPM cutting without exceeding maximum SFPM. Just remember that high RPM cutting with larger tools will require adequate power. For example, cutting aluminum with a 1”, 4 flute cutter running at 30,000 RPM will require a spindle that can deliver around 60 HP!

6. What Are the Worst Applications for High Speed Spindles?
High speed spindles are high RPM, low torque devices. They use AC motors that provide constant torque up to base speed. Since power is equal to (speed x torque), power increases in a linear way as RPM increases. This type of spindle generally does not have high torque at low speeds. Typical low speed / high torque operations cutting harder materials (think large face mills or roughing end mills) will not be well supported using most high speed spindles. This is the primary reason why high speed spindles are used to finish steel molds, not rough or semi-finish hard materials. The roughing is done on one machine and the finishing is done a specialized, high speed machine. The resulting benefit is a superior, qualified surface that does not require any hand finishing. Saves time and money!

7. I Have An Old CNC Machine. Can I Install a High Speed Spindle On It?
It is possible to retrofit a high speed spindle on most old CNC machines. The main spindle is removed, and a new high speed spindle can be installed, completely integrated with the CNC and ATC. However, the decision whether to do this or not depends completely upon your application. One of the easy benefits of using a high speed spindle is a significant increase in feed rates. However, an older CNC machine often will not be capable of maintaining required high accuracy moving at higher feed rates. So, if your need is to do high speed contouring (mold finishing), your part may look great but be inaccurate. If, however, your application is drilling many small diameter holes, a 50K high speed spindle can do a much more productive job when compared to the old 6K main machine spindle. It is a good idea to consult with your spindle supplier to see if your old CNC machine is a viable candidate before you invest in any upgrades.