The Problem
Electrospindles, commonly found on CNC stone machining centers, are very service
prone and costly to repair. In fact, it’s not uncommon for some machines to require
spindle service on a yearly basis costing the machine owner $12,000 to $20,000 or
more. The reason that electrospindles are so problematic is that they have been
designed to fit into a rather small container. In that container, the spindle, bearings,
windings, and various sensors are positioned in very close proximity to each other.
Only a small seal separates water from electricity. As the spindle produces power,
the motor windings generate heat that has to be eliminated quickly before damage
to the spindle bearings occurs.
The Solution
Northwood engineers turned to the machine tool industry for ideas because spindle
problems like those common in the stone industry are virtually unheard of in the
machine tool industry. The resulting breakthrough technology is Northwood’s Extended
Duty Spindle (EDS).
Heat, the Enemy of Spindle Bearings
The EDS keeps the spindle and motor separate, which solves a major design problem
-- heat near the spindle bearings. Motor windings generate heat as they produce
power and if that heat is allowed to enter the bearings, premature bearing failure
is the probable result. To overcome this problem, electospindles commonly require
spindle chillers (refrigeration systems that circulate cold water around the motor
housing to dissipate the heat before it can get to the bearings). The EDS separates
the spindle and motor, eliminating the need for maintenance-prone refrigeration
systems. In addition, because the spindle motor is separated from the actual spindle
(and includes a built-in cooling fan), motor windings can be included that produce
power characteristics that are ideal for machining stone!
Eliminating the “Middle-Man”
Traditional electrospindle designs require the use of a spindle drive, a separate
computer that controls the spindle (direction of rotation, RPMs, power, etc.) Think
of the spindle drive as a “middle man” – the machine control tells the spindle drive
what to do, and in turn, the spindle drive tells the spindle what to do. The system
is even more complicated because information from the GE Fanuc machine control is
in digital format, and the spindle drive converts it to analog format as it communicates
with the spindle. The “middle man” in this example serves as a translator because
the machine control and spindle don’t speak the same language.
The EDS overcomes this language problem because the spindle motor is a GE Fanuc
spindle motor that is designed to communicate directly with the GE Fanuc machine
control digitally. The “middle man” has been eliminated because they both speak
the same language, and the machine control is in constant communication with the
spindle motor.
Rebuilding/Replacing the Extreme Duty Spindle?
With traditional electrospindles, if a motor winding or spindle bearing is bad the
entire electrospindle has to be replaced. With the EDS, only the defective part
needs replacement or repair. GE Fanuc spindle motors are some of the most reliable
in the world, with some having lasted for decades, so the probability of needing
to replace a spindle motor is very low. But if the need for repair or replacement
ever arises, the EDS can be rebuilt for as little as $2200, and the entire spindle
unit’s replacement cost is just $8,000.