If the spindle is all good on my opinion maybe it lacked the RPM the way it used to be, how many RPM is your spindle? I crashed some of the spindles on our units but usually I only get a broken tool bit or a busted fuse from abrupt crashing causing the amperage of the controller to spike and exceed the fuse amp. rating thus blowing it. I also experience broken tool bits by accidentally cranking the speed control knob half way making the spindle turn slower than it used to be while the movement of the XYZ is still the same then voila! I just snap a carbide tool bit...ohh well