Right, and I did that. The prob is always that the top knob either bottoms out on the bottom knob, or that it won't rotate cleanly within the "shroud" encompassing the outside of the top knob. This is especially true about those awful, awful standard EMG knobs, but can be true of the aftermarket metal knobs, too.
I have found a solution: space the upper knob upwards. I filled the center shaft hole of the upper knob with some material that will allow the top knob to keep the spacing between the upper and lower knobs. Now it works. In my case, I used a simple chunk of paper towel. Works fine now.
I'll have to remember this.
The prob is with EMG: they don't allow for panel thickness variances in stalling the concentric pot, therefore the knobs apparently only fit properly on thin panels. Also, why in the he77 they use a D-shaped shaft on the upper (treble) knob is beyond me. Really limits the knob placement as the knobs have a set screw, and the only way to really adjust the knob rotation positioning it is to re-align the entire pot rotation. In many cases this is not possible because the large electronics on the pot will hit something inside the cavity. EMG are you listening? Didn't think so.
Thanks.