Proper troubleshooting helps identify and resolve issues quickly, minimising downtime, while routine maintenance prolongs the machine’s lifespan and keeps it in optimal condition. By understanding and implementing these practices, you will prevent common issues, ensure quality cuts, and maintain a safe working environment.

Troubleshooting Common Issues

• Recognising Issues through Sound: although a woodshop can be a very noisy environment, listening to the sound of the cut is an effective diagnostic tool. Changes in pitch or unusual sounds often signal issues, such as:
  1. High Pitch Whining: Can indicate excessive spindle speed or insufficient feed rate.
  2. Dropping Torque: Can indicate the feed rate or chip load is too high, or the spindle speed is too low to sustain the cut.
  3. Grinding or Chatter: Can be caused by an incorrect feed rate, spindle speed, dull tool, loose tool holder or insufficient workholding.
  • Solutions: Adjust the feed rate or spindle speed according to material specifications, replace or sharpen tools, ensure the tool holder and workpiece are securely clamped.
• Poor Surface Finish: There are a number of reasons why the finish quality of a cut may be of low quality, including:
  1. Dull Tools: Dull tools can have inconsistent cutting characteristics and dimensions which differ from those specified in the CAM tool libraries, which can result in poor quality finishing or inaccurate dimensions. As a tool heats up, its ability to cut cleanly can become reduced. Different tool materials and hardnesses can respond differently to machining different materials.
  2. Material Issues: Glues, additives and natural material properties (such as sap) can build up on cutters, causing effects similar to dull tools.
  3. Machining Strategy: The same result can often be achieved with different machining operations, however this does not mean that they will be identical. It is important to understand how different CAM operators can approach a problem quite differently, and each approach will give a different result. Conversely, many operators may produce similar or identical results but take significantly different amounts of time to achieve.
  • Solutions: How to improve surface quality depends a lot on where the problem comes from. Perform test cuts to ensure quality is as expected, replace or sharpen tools on a regular basis, test different materials and their results. For machining strategies, set up test programs to perform all the types of cuts you will be using, and iterate until you find a strategy which results in suitable quality and speed compromise.
• Accuracy, Repeatability and Maintenance:
  1. Large-scale Dimensional Accuracy: Larger scale dimensional accuracy should be very good on the CNC. If you are finding larger dimensions are not matching, contact a maintainer. The issue may lie in areas such as belt tension, backlash, or rigidity. In any case, making changes to dimensional accuracy affects all users and requires accurate measurements and specific techniques. It should only be undertaken by a skilled maintainer.
  2. Small-scale Dimensional Accuracy: Small dimensions requiring accuracy, such as slots or holes intended for mating pieces or hardware, are commonly not the correct dimensions even if the model, tool and machine are in excellent working order. This is due to a myriad of small effects, however the resulting innacuracies are generally small and stable. Design these dimensions using nominal dimension on your model and then adjust the dimensions as cut using the ‘Stock to Leave’ variable found in most operators. There are other methods but this is a simple and repeatable way to achieve accuracy in small dimensions.
  3. Eccentricity, Patterns or Directional Inaccuracy: Due to how some parts of the machine are controlled, and their mechanical connections to other parts, inaccuracies in specific systems can result in inaccurate output which can have characteristics or patterns that can help identify where these issues arise from. For example, a common issue is backlash, or the imprecision inherent in changing directions using a control system; a circle cut on a CNC (or other machine) becomes an ellipse if the reversal of movement has some play in it. Fixes should only be undertaken by a skilled maintainer.

Regular Maintenance

All users are expected to assist in the maintenance of the machine, but what this means will be unique to everyone.

• All users are expected to report on issues they encounter, any broken parts or maintenace tasks they believe to be required.
• No user is expected to do maintenance they have not been trained to perform, or are in any way uncomfortable undertaking.

Beyond this, as a shared machine, the more users who are able to fix minor issues, the more reliable the machine will be for everyone. Take the time to read up on maintenance of CNC systems, and engage with the group on how you can offer your time, skills and knowledge to everyone’s benefit. It is never expected, always appreciated.