One of the most common and serious problem in a cnc machine is the step loss. In very poor words it means that a pulse coming from a parallel port cannot reach the motor (or it is not recognized by the motor driver - or it is not executed by the stepper motor).

Obviously the lost of even very few steps can compromize the quality and the accuracy of the manufac milled by the cnc machine. Difficult, sometimes, to recognize where and why a system is suffering from steps loss but there are a few but important rules to follow to prevent this malfunction:

• the power supply: the double power (motor and electronics) should be separated, well filtered, smooting capacitors well dimensioned, with a circuitry designed to keep the ripple factor and noise as lower as possible;
  
  
• avoid the use of the speed where resounance phenomena are evident;
  
  
• use recently build motors; technology and materials are changed during the last years;
  
  
• be sure that the duration of the step coming from the parallel port is long enough to be certainly recognized by the chip driver (all cnc software permits, during the setup, to fix this parameter);
  
  
• don't use the full step to drive the motor; half step (or even more) is less sensible to phenomena like resonance and magnetic hysteresis;
  
  
• keep the cables inside the box far from the power supply, particularly from the transformer;
  
  
• reduce, if necessary, the speed of the cnc machine. The torque of the motor is inversely related to the speed;
  
  
• disable the network cards (trough the bios) of the motherboard of the computer ( absolutely not necessary using ubuntu and EMC2 because, sysem updates are forbidden);
  
  
• disable any software or utility that 'check' periodically the mainboard (temperature, speed, system monitors etc).