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How Fast Can a High Speed Spindle Operate?

The maximum speed a high speed spindle can go is determined by several factors, including tooling size and power of the motor. It all comes down to bearing diameter. All bearings are built to run up to a maximum working speed for a useful life. Other variables, such as bearing lube method and loading, also affect the top speed. Small high speed spindles can run up to 180,000 RPM, but for practical milling and drilling speeds of 20K ~ 50K are common.

High Speed Spindle
How Fast Should I Be Running My Tool?

The maximum RPM you should be running is based upon the cutter diameter, type of tooling you are using (HSS, carbide, coatings) and the material you are cutting. Every material has a maximum surface cutting speed SFPM recommendation from the cutter manufacturers. This value is based upon the friction and heat created between your cutter and part material as the cutter removes material (drills or mills) from the part. Basically, the RPM is faster in aluminum and slower in steel.

How Long Will My Spindle Last?

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. Typically, the spindle life is limited by the mechanical life of the ball bearings. Proper maintenance, using correct cutting parameters and minimizing vibration due to imbalance will optimize spindle life. In most cases, a typical spindle will operate for an average of 6000 hours before a rebuild is required. Overloading crashes or operating without proper cooling and lubrication can significantly reduce spindle life.

Do My Tools Need to Be Balanced?

Imbalance creates damaging levels of vibration. The level of vibration force increases with the square of the RPM. For low speed spindles, under 10KRPM, vibration forces may not be severe. However, for high speed spindles, vibration due to imbalance 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.

What Are The Best Applications for High Speed Spindles?

Many applications are well suited for high speed spindles. These include any milling or drilling with minimal diameters. A small tool only reaches peak SFPM when run at high RPM. This allows the most productive feeds and speeds. Also, all soft material cutting (think aluminum, plastics and composites) can utilize very high RPM cutting. Just remember that high RPM cutting with larger tools will require adequate power.

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 as RPM increases. This type of spindle generally does not have high torque at low speeds. Typical low speed – high torque operations cutting more complex materials (think large face mills or roughing end mills) will not be well supported using most high speed spindles.

Can I Rigid Tap Using a High Speed Spindle?

Rigid tapping requires the CNC to monitor and control the spindle position in coordination with the Z-axis. High speed motor spindles can be operated in both open-loop and closed-loop modes. In simple open-loop modes (most small spindles), the CNC does not monitor the spindle position directly. These spindles are typically not capable of rigid tapping. If the spindle is used in a closed-loop mode (larger CNC spindles), it is possible to perform rigid tapping since the CNC accurately monitors and controls the spindle encoder. However, the maximum tap size will be limited based on the size of the spindle motor (power and torque limits).

Are All High Speed Spindles Liquid Cooled?

High speed motor spindles use electric motors and ball bearings. The bearings and motor generate heat. The heat must be removed to ensure long bearing life, accuracy and optimum performance. For small spindles, air cooling often is sufficient to provide this cooling. For larger spindles, liquid cooling, water or oil is used to remove heat from the spindle. The cooling liquid is circulated through a temperature-controlled chiller. The typical cooling temperature used is 26° C (78.8° F).

How Do High Speed Spindle Bearings Work?

Most modern high speed spindles use high precision, angular contact, hybrid ceramic ball bearings. The accuracy rating is typically ABEC 7 or ABEC 9. This type of bearing offers the ability to support both axial and radial loads. Pre-load generally is light to medium, depending upon the desired maximum speed. Bearing lubrication is critical and may be as simple as grease or a more complex oil-air injection system.

What Are the Possible Tooling Systems on a High Speed Spindle?

Every high speed spindle needs a tool to do some work. It may be a milling cutter, drill or grinding wheel. It is possible to have different tooling options. The most simple is a precision collet, like ER. The tool shank clamps directly using a collet and locking nut. Grinding arbors are also possible. For applications that require multiple tools, quick-change tooling systems are possible. These include CAT and BT with RPM limits of 15KRPM and HSK. The HSK system is designed to operate at very high RPM.

Can I Get Coolant Through the Tool on a High Speed Spindle?

Yes, coolant through the tool is possible on high speed spindles, even up to very high RPM. There are special rotary couplings available to support coolant flow up to 60,000 RPM. However, the coolant pressure required may influence the maximum spindle RPM. These rotary couplings use precision ceramic seals and need coolant filtering to remove chips and debris.

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. However, whether to do this or not depends upon your application. An older CNC machine usually will not maintain high accuracy moving at high 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 depends upon what you want to do.

Can I Run Multiple Spindles At the Same Time?

Many applications justify using more than one spindle. Swiss machines, special machines and dedicated process systems can utilize multiple spindle systems. For these systems, it may be possible to share support components and reduce overall costs. Cooling and lubrication systems can often be shared. Drive systems can sometimes be shared, depending on the motor type (AC or Brushless DC), required speeds, and other factors.