DIY CNC Electronics

 

The electronics aspect of the cnc build proved to be the most thought - provoking and elusive part of the cnc build. My system was designed to use stepper motors. For a novice like myself with very basic knowledge of electronics. A stepper based system seemed like a viable solution. A few elusive problems surfaced after the machine was up and running.

 One detail that came to light was using a stepper motor that was too small for the application. Case in point was the Z axis of the machine. Gravity affects the Z axis more than the other axes. Using a 300 oz in motor just could not move the axis reliable up and down. Add to my delusions of running the Z at 100 ipm and the situation became worse.

Bob Campbell CNC Control PanelAfter a few months of trial and error I came to the conclusion that I should switch out the motors and try servos. I did resolve the problem when I switched to a large servo with pulley reduction. I believe the lack of reliable performance were related to my lack of knowledge regarding the use of shielded wires, proper grounding techniques and motor sizing.

The term that comes up frequently in the DIY CNC user groups are issues of EMI or Electromagnetic interference. This interference can cause a stepper to lose position and aversely affect the correct dimensional positioning of the cnc machine. This applies to a servo based systems also. Here is a link I found that deals with issues of interference.

 Another concern after extensive research in various usergroups was where you rout the various wires from the control panel to the motors on your machine. It is recommended to keep the encoder wires away from the motor power lines. In my case I routed the encoder wires on the outside of the cable carrier. This helped to minimize interference from the higher voltage and currents of the servo motor power supply lines.

Servo Motor

 I would never be bold enough to make a recommendation as to which motor type is the correct choice. I`ll just mention some of the pros and cons of the two motor types..The cost of a stepper system is less then a servo. Steppers can be direct drive which saves expense. They also have their own set of problems related resonance resulting in lost steps.

Servos require a timing belt and pulley reduction to achieve their maximum performance. This adds additional costs to a servo system. Servo systems can be prone to adverse affects of interference. When I switched to servos. I purchasing differential servo wiring which were premade by US Digital to minimize EMI problems. This added nearly $140.00 to the price of the servo system just for the encoder wires.

Stepper system control panel

Here is the original control panel for the stepper motors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After years of using the cnc. I decided to rework the control panel. The picture above was circa 2004 with a stepper based system. The new control panel is under construction for the servo based cnc.

New Control Panel

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