I’ve got a Hitachi P20SB that I picked up off of Ebay a few months ago, and now that I’ve finally gotten around to using it, I’ve found that the depth adjustment knob is seized. I’ve tried muscling it, I’ve tried having bigger guys muscle it, and I’ve tried having even bigger guys muscle it, all to no avail. Is there much I can do aside from sticking some WD-40 in the threads and hoping for the best? It’s seized in the lowest cut depth if that’s of any interest.
If I remember right, under the sticker on top of the knob is the nut molded into the plastic knob. You could try putting a little lube in from there. Are you sure you’re turning the knob the right direction?
That thread is a very sloppy cut, not a precision-fit with a specific nut. Very easy for the nut to cross-thread on the stud and become stuck. It’s a mechanical issue and there may be damage (from forcing it), so it needs to be taken apart and assessed. Maybe contact Jeff at US Blanks (who distributed the last ones) and see if he has parts. I will keep my opinion of the Hitachi conversion design to myself.
Success! After using some WD-40, tapping with a hammer periodically, and lightly maiming the knob with a pair of channel-locks, I got the knob to turn. Thanks for all the input everyone!