Last night, while cutting several 3/4" dados, I experienced (for the first time) a change in blade height!! At first I thought I wasn't feeding the stock correctly, but then I noticed the height adjustment handle HAD moved about 90° from where I set it (yes, I set it on the up-stroke). I reset it and it moved down AGAIN. I had to clamp the adjustment knob to keep it from changing. Up to this point (about 2 years) I had not noticed this happening. I could find nothing in the manual on how to adjust/tighten the adjusting mechanism (model 2400). When searching this site for a "add-on" blade height lock, all I could find was "never a problem" with this (missing) feature. I did have a large initial cut depth initially (1/2 inch deep) but the height continued to change even when I was trying to clean-up the parts that were cut too shallow. What a pain... almost 2 hours for four 22" long dados. I was thinking of drilling and tapping the rotating portion of the knob and putting a set srcrew with knob... Any other suggestions??