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What YOU
NEED TO KNOW,
Before
Investing in a CNC Router ...
YOU NEED TO KNOW THE
ADVANTAGES OF:
>
Servo
Motors over Steppers
> Ball
Screws over Acme Screws and/or Rack-and-Pinions
> Rigid
Machine Frames over Table Top Routers
> A
Windows-Based CNC GCODE Interface
Servo Motors over Steppers
All Techno machines, except for the Stepper
DaVinci, feature servo motors, not stepper motors. With servo motors, you can achieve greater power and speed. Our competitors play a numbers game of specifications we do not. We actually can achieve specifications better than what we claim. When we claim speeds of 200 inches/minute, we can usually go 250
ipm. When we claim a repeatability of .0005 inches, we can and do achieve repeatability better than that, and so on. The speeds claimed by some of our competitors on their machines can only be achieved if they throw the machine off a cliff. Stepper motors are always prone to vibration and can result in a loss of steps. Even micro-stepping is not a guarantee of eliminating this. When a motor is run open loop, the resulting vibrations from a heavy cut can cause all sorts of problems and without the encoders to tell where the motor actually is, you can always have problems.
To View a
Compare-Contrast Table on Servo and
Stepper Motors,
Click HERE
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Ball Screws over Acme
Screws and/or Rack-and-Pinions
Techno only use ball screws and anti-backlash ball nuts on ALL OUR MACHINES. Acme
screws are very inefficient and combined with stepper motors can compound the problems. Rack and
Pinions can be an endless source of problems. When chips or dirt falls on the rack, the pinion gear has to go “over it” resulting in loss of positioning accuracy and vibration. The racks constantly need adjusting to tighten them and after tightening them in one spot, you are more than likely to be too loose or too tight on another area of the rack. This of course causes the system to be either too loose or to bind. This does not happen with a ball screw because the balls roll over a formed thread. Since they roll, we can tighten up the fit between the screw and ball nut without causing the system to bind. Racks and acme screws wear because of the nature of their action they have to rub and they have to have a certain amount of looseness to achieve their motion. In both the rack and Acme screw, the sliding action causes the wear, which requires the adjustments. The rolling action of the ball screw means that the motion of the system is first of all more efficient so that the motor power is used to move the system, not just used to overcome the sliding friction of the mechanism, but second it does not wear as much or as fast. Putting it simply, rubbing wears material out, rolling does not. This means that our customers spend their time running the machine, not adjusting it.
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Rigid Machine Frames
over Table Top Routers
Techno machines, especially our larger CNC machines, are built on rigid steel frames, not bolted assemblies or sheet metal covered aluminum assemblies. This results in stiffer frames which means that when you take heavy cuts, our machine will not rack or twist. Our CNC lathes are designed with covered mechanisms to prevent chips from getting where they should not. Our CNC wood lathe has the entire moving mechanisms covered in sealed slides and the seals are on the bottom of the mechanism so that the wood chips have an even more difficult time of getting in the machine
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Windows-Based CNC GCODE
Interface
Techno's WINDOWS-BASED CNC GCODE Interface is extremely user-friendly with most major functions just one-click away.
Even users that are unfamiliar with computers can get up and running in
no time. Techno provides easy to follow Interface Tutorials
that walk you through the processes. It's simple to install on any
Windows-Based PC (WIN 95 / 98 / 2000/ME/XP) so you don't have to
worry about compatibility. The Interface's Main Menu (shown at right) highlights Techno's single-screen design. Some of the features that one-click will take you to, include:
· Toolpath Previewer
· Built-in GCODE Editor
· Production Logging and Reporting
· Toolbreak Auto-Repositioning
· Infinite Look-Ahead and Continuous Motion (optimizing feedrates while maintaining accurate positioning)
AND, all of Techno's complete system machines (LC, RG,
Prem Class, etc.) get this software bundled with the machine, FOR FREE. AND,
you get FREE lifetime updates on this software, via the Internet.
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Servo-Stepper Motor Table
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Maintenance
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Stepper
motors are brushless. They
experience little or no wear, and are virtually maintenance-free.
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Brush-type servo motors require a change of
brushes, typically, after 5,000 hours of heavy use otherwise they
are virtually maintenance free.
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Cost
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In general, stepper motor systems tend to be only slightly
less expensive than servo motor systems and the price difference
is getting smaller.
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Servo motors in the NEMA23 frame size tend to be 5% to 15%
more expensive than similar stepper systems.
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Resolution and Accuracy
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For a given screw pitch, typical four phase stepper
motors can produce 200 full steps, 400 half steps, and up to
25,000 micro steps per revolution.
It is significant to note that since the stepper motor is
open loop, it does not necessarily achieve the desired location,
especially under load. Particularly
poor positional accuracy can result when using micro stepping,
which is mostly useful for smoothness of motion.
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Servo motor resolution depends upon the
encoder used. Typical
encoders produce 2,000 to 4,000 pulses per revolution, and
encoders with up to 10,000 pulses per revolution are available.
Since servos are closed loop, they can and do achieve the
available resolution and they are able to maintain positional
accuracy.
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High Speed and Power
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Steppers have very poor torque
characteristics at higher speeds.
This condition is improved only slightly by microstepping,
however, unless the stepper is used in a closed loop mode, it does
not usually perform as well as a servo. Once the stepper is used
in a closed loop mode, it usually becomes more expensive than the
servo system of comparable size.
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Servos can produce speeds and powers two
to four times that of similarily sized steppers. This improvement
is a direct result of the closed loop (i.e., constant position feedback), which allows for higher speed and
greater reliability. The
closed loop nature of the servo also allows such a system to better
utilize peak torque capabilities.
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Open Loop compared to Closed Loop
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Stepper motors are almost always used in
an open loop configuration. This means that the motor is commanded
to move a certain amount but the computer does not know if the
motor has or has not moved that amount. In some cases, resonance
or vibrations can cause a stepper motor to lose steps or stall out
before completing the motion.
This is an ever-present possibility.
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By nature, servomotors have constant position
feedback from the optical encoder. This device sits on the back of
the motor and keeps the controller informed of how far the motor
has ACTUALLY moved. This
position feedback is used to correct any discrepancy between a
desired and an actual position.
This constant corrective action results in faster speeds
(up to three times the throughput), and increased power (up to
three times the torque) at high speeds.
The closed loop nature of the servo also ensures that
stalling cannot occur unless there is an immovable object in the
path.
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3D carving and contouring
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Steppers can be made to do 3D carving
applications but because of the drop in torque at high speeds,
they usually have to move slower than servo motors to make sure
the motor does not stall or miss steps.
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Servos can perform high-speed continuous motion
much more reliably, making them much better than steppers in
three-dimensional contouring applications.
We have found time reductions of up to 80% on some
applications. The
continuous motion also results in better finish quality.
In addition, the servo's reliable high-speed continuous
motion can reduce the possibility of scorching and melting when
working with woods and plastics.
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