How to Integrate a High Speed Spindle into Your Shop

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These days, most of us have heard about the benefits of high speed machining: reduced cycle times, better surface finish, longer tool life, faster feeds for small diameter mills & drills, and better machine utilization. High speed machining will require having a spindle capable of over 10,000 RPM. That all sounds great, but, high speed spindles are very expensive and have different tooling, etc. So, exactly how do you successfully integrate a high speed spindle into your shop environment?

Let’s start by looking at the various types of high speed spindles that are available today. The most basic type is known as an adapter type speeder head. This is a mechanical device that fits into your standard machine taper (HSK, 40 or 50 taper). It is essentially a gear box with a collet to hold the tool that multiplies the machine spindle RPM to a higher output RPM. Often, the speeder head can be loaded into your tool changer magazine and swapped out, as needed. This type of head can provide high torque and up to 20,000 RPM using grease packed bearings and a planetary gear. On the benefit side, this type of head is inexpensive and easy to integrate. On the negative side, over time, the gears create heat and unwanted vibration levels and may not have a very long life before a rebuild is required. However, if you only need to run at high speed occasionally, for example light finishing or engraving, this may be a good solution.

The next type of adapter type high speed spindle uses a compressed air driven motor. These spindles also feature a precision collet system to hold the tool and fit into your machine taper and ATC, like the speeder head. A special block would be installed on your machine to pass the compressed air to the head. These spindles usually offer a much higher RPM than a mechanical head (up to 60,000 RPM), but the power and torque of the motor at certain speeds can be limited. The bearings may be grease packed ceramic or, even air bearings. These spindles are best applied for higher speeds and very light cutting, not low RPM. So, if your need is for limited, very small tool operations, this could do the job. 

Finally, we come to electric motor spindles. Electric motor spindles are available in many forms, however, the most common type is an integral cartridge design. To obtain the highest power, we like a motor that has a reasonable diameter (to generate torque) and length (to provide power). Since we need to hold a cutting tool to do any actual work, the spindle will have either a collet system or removable tool holder (CAT, BT or HSK). This type of spindle can be applied in a few different ways.

Electric motor spindles use a variable-speed, AC motor and must be connected to an external power supply to control the motor speed and power. Power can range from less than 1 HP up to 125 HP, with speeds up to 60,000 RPM. Some smaller sizes use air cooling, while larger types require liquid cooling. The spindle bearings require lubrication in the form of grease or oil mist. The spindle support system would include a chiller, bearing lube unit and motor controller. Often a PLC is included to interface with the machine tool CNC, however, a simple manual control can also be used.

So, once we cross over to an electric spindle, what is available? 
There are adapter type, electric high speed spindles. These spindles will fit into your machine taper, and may be loaded by hand or from your ATC. In some cases, the spindle cannot be stored in the ATC but can be held in a cradle in the machine and loaded by M code when needed. The power can range from 1 HP up to 15 HP. Speed can vary, but for the lower power spindles you can reach 80,000 RPM. The higher power units can reach 35,000 RPM. The main benefit of this type of spindle is higher power, higher speeds and a longer life. Although more expensive, electric spindles are designed for continuous operation and satisfy high production requirements much better than a geared or pneumatic head.

The next solution is a fully integrated, high speed spindle installed in your CNC machining center. This can be utilized in two ways: as an auxiliary spindle adjacent to the main spindle or as the main spindle, integrated to the ATC. This is the most expensive solution, but also provides the most capability. 
An auxiliary spindle would be mounted in a bracket next to the main spindle. It may utilize a manual tool clamping collet or a removable HSK tool holder. The main benefit of this approach is that you still retain all the benefits of your main low speed, high torque spindle for roughing and semi-finishing and add the benefits of the high RPM for finishing operations. This is used very successfully for many tool and die applications. However, as you are limited to only one cutter on the high speed spindle, the applications are somewhat limited.

Finally, a fully integrated spindle system on a machine offers the ability to use the high speed spindle with multiple tools and is fully programmable with the ATC. You may either purchase the complete system from an OEM, or, retrofit a high speed spindle into an existing machine tool. This is becoming more common as more shops use high speed on a daily basis. For aluminum and plastic cutting, high speed can be very effective to reduce cycle times and provide super surface finish. For harder materials, like molds and dies, superior surface finish can be achieved. To be successful, however, the machine, spindle and cutters must be set up and programmed to optimize the application.