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A crowd
develops at the end of a service call, everyone wants to see if their CNC
machine was really fixed and running again - to hear first hand
the elusive results of a long standing service where a problem
would happen for an instant every 4 to 8 hours.
How could a loose wire on the tool clamp confirmation limit
switch, fifteen feet up above the spindle draw bar cylinder, cause damage to a thread hobbing tool insert, once every
4 to 8 hours?In the final
analysis, the hobbing operation created heavy vibration which
opened the switch circuit. The unexpected dropped switch signal
triggered the CNC ladder sequence to command a
change in the spindle rpm, which would then damage the expensive hobbing tool
working the material. The unexpected change in spindle rpm also caused a
sharp vibration that would coincidentally re-seat the loose
switch wire for another 4 to 8 hours of running. Moving
the plastic insulator that was pinched in the switch connection
screw solved the problem. Finding the problem took a while
using test equipment, diagnostics and a fair amount of patience.
I have spent 21 years solving some of the toughest service problems at
thousands of the best machine shops in North America. On the
job, we apply a set of standard techniques to solve complex
service problems. Please use these basic guidelines to
gauge the results of your next service visit.
Thank You and Best Regards,
Daniel D. Nelson
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