Dear A Tech...
"I recently bought a three year old, gently used CNC mill and discovered it's not repeatable and I'm
having problems maintaining min. tolerances. Can a technician call me about fixing this? I'm getting
conflicting reports from three service guys!" Thanks, Desperate.
Position errors are very common and are typically caused by worn-out ballscrews being used as
positioning devices, physical deviations in the machine being transferred to the finished part, or by encoder
feed back errors.
Our technicians are routinely called out on these "mystery" types of problems. Experience has
trained us to first analyze the type of error being reported in order to reduce the possibility of chasing
erroneous causes. You stated in your email that your machine is not repeatable. Non repeatability can be
caused by your encoder missing counts, ballscrew growth, or a control component failure. Since today’s
controls use stable solid state electronics with no moving parts, failures are rare. So, let’s focus on the first
two causes: encoder miscounts and ballscrew growth.
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