What You Need to Know... Before Purchasing a CNC Router

• Servomotors over Stepper Motors
• Ball Screws over Acme Screws or Rack-and-Pinions
• Rigid Machine Frames over Tabletop Routers
• A Windows®-Based CNC G-CODE Interface

Servomotors over Stepper Motors

All Techno machines, except for the Stepper DaVinci, feature servomotors, not stepper motors. With servomotors, you can achieve greater power and speed. Our competitors play a numbers game of specifications that we do not. We actually can achieve specifications better than what we claim. When we claim speeds of 200 ipm, we can usually go 250 ipm. When we claim a repeatability of .0005", 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 microstepping 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.

Stepper Motor and Servomotor Comparison

Maintenance: Stepper motors are brushless. They experience little or no wear, and are virtually maintenance-free. Brush-type servomotors require a change of brushes, typically, after 5,000 hours of heavy use; otherwise they are virtually maintenance free.

Cost: In general, stepper motor systems tend to be only slightly less expensive than servomotor systems and the price difference is getting smaller. Servomotors in the NEMA 23 frame size tend to be 5% to 15% more expensive than similar stepper systems.

Resolution and Accuracy: For a given screw pitch, typical four phase stepper motors can produce 200 full-steps, 400 half-steps, and up to 25,000 microsteps 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 microstepping, which is mostly useful for smoothness of motion.

Servomotor 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.

High Speed and Power: Stepper motors have very poor torque characteristics at higher speeds. This condition is improved only slightly by microstepping; however, unless the stepper motor is used in a closed-loop mode, it does not usually perform as well as a servomotor. Once the stepper motor is used in a closed-loop mode, it usually becomes more expensive than the servomotor system of comparable size.

Servomotors 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 servomotor also allows such a system to better utilize peak torque capabilities.

Open-Loop compared to Closed-Loop: 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.

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 servomotor also ensures that stalling cannot occur unless there is an immovable object in the path.

3D Carving and Contouring: Stepper motors 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 servomotors to make sure the motor does not stall or miss steps.

Servomotors 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 servomotor's reliable high-speed continuous motion can reduce the possibility of scorching and melting when working with woods and plastics.

Ball Screws over Acme Screws 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 fall 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.

Rigid Machine Frames over Tabletop 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 into the machine.

Windows-Based CNC G-CODE Interface

Techno's Windows®-Based CNC G-CODE 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 highlights Techno's single-screen design. Some of the features that one click will take you to, include:

• Toolpath Previewer
• Built-in G-CODE 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, Premium Class, etc.) get this software bundled with the machine, FOR FREE. AND, you get FREE lifetime updates on this software, via the Internet.