If CNC Spindles Had Odometers Like Cars, How Far Would They Run?The electro-spindle is a very complicated piece of machinery. Most of the components are made out of specialized steels that must be machined with exacting precision, be durable enough to handle high centrifugal forces for thousands of hours and hold up to the wear and tear that comes from high feed rates.

If we kept track of the mileage of spindles, as we do our automobiles, a typical 24,000 rpm spindle used eight hours a day would accumulate over 250,000 miles per year. Eventually, the bearings wear out or the electrical insulation fails. The spindle will be in need of repair sooner or later.

When that time comes, you would hope there is still product support from the manufacturer. Spindles made in the late 1990’s and early 2,000’s were limited by inverter technology. An inverter, also known as a VFD, changes incoming grid power at 60 hertz to a higher frequency and a different voltage. Without an inverter, motors would only be able to run at 60 hertz. Most inverters during this time were limited to 400 hertz operating frequency.

Two pole motors were more common back then because the spindle could reach 24,000 rpm at 400 hertz, and 4 pole motors were limited to 12,000 rpm. The speed of the motor is equal to the frequency multiplied by 120 and divided by the number of poles. As inverter technology improved and higher switching frequencies were attainable, the market slowly shifted to four pole motors. Four pole motors can produce more torque at lower rpms, which broadens the useable speed range for machining operations.

This shift to four pole motors led manufacturers to stop supporting two pole motors in the sub 24,000 rpm range. As a result, there are a lot of older two pole spindles still in use but without any product support from the manufacturer. In most cases, the only option available is to purchase a new spindle with a four pole motor. The problem with going from a two pole to four pole motor is the additional need of a higher frequency inverter. A new inverter can cost hundreds of dollars and it comes with the hassle of installation and programming.

In an effort to offset the need for a new inverter, we offer two pole motors in the most common power ranges. The 106B-I30-2 and the 135B-I30-2 are ISO-30 spindles. Adapter plates are available to mount these to the pre-existing mounting features. The spindles are air cooled instead of liquid cooled to make installation even easier. We also can assist with sensor connections to keep the PLC working seamlessly.

Tony Maffeo is founder and chief engineer of HS Spindles, Santa Ana, CA. 

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