Selecting a New Motor and VFD for Your
Industrial Hobbies Mill

The Industrial Hobbies mill is designed to have an operational range from 100 to 1500 RPM with a low speed motor (included) or 200 to 3000 RPM with a 3400RPM spindle motor we supply. 

Operation in the low speed range is fairly straightforward:  Connect the mill to power, add suitable oil and away you go.

Running in the high-speed range takes a bit more adjustment, and is outlined in the following steps.

When selecting a VFD and motor combination for the mill keep the following guidelines in mind for maximum machining performance.

Select the Motor

Metric Motors have a base/frame combination that correlates to the horsepower.  The motor that ships with your mill is a 2 HP B5 Flange motor with a shaft cut down to the D80 frame size.

A 2 HP motor will provide increased performance at the higher RPM’s where frictional fluid losses are the highest.  Of course selecting the proper oil helps significantly as the fluid losses for a lighter oil are much less than that of a thicker oil.

* Will need to have the shaft cut down to the D80 size, which is available from motor repair shops for a nominal fee.

**  Do not use a motor greater than 2HP. If you do losing  your warranty may result. 

Selecting the VFD

A Variable Frequency Drive (VFD) is what converts single phase power to three phase power for the motor.  Because a VFD is a solid-state device and it has built in current limiting and protection circuits it will become the weakest link in your conversion to high-speed operation.  Selecting a VFD that is in the next size range up from the motor you are choosing will give increased performance and less problems than one that is an exact match.  This is because motor loading is measured over a period of time (thermal time constant) but it is possible to have short periods of very high current draw that will shut down the VFD, yet not adversely affect the motor.

Now of course VFD’s vary from manufacturer to manufacturer and you should discuss proper applications of their product with them.

Final Notes on High Speed Operation

Above 2000 RPM total machining power is actually decreasing as frictional fluid losses rise exponentially above that RPM.  These losses show themselves in the form of additional current draw from the motor and an increase in head/oil temperature.

For aluminum (most common machined material) peak material removal rates will be found in the 1700 to 2000 spindle RPM range and best final finish will be found at 3000 RPM.

Do not try to achieve high-speed operation on the first day, give your machine 10-20 hours of 1500-RPM operation to break in before hand.