Michael, what bit angle on the router bit. 45 or 60 degree ?More pics
More details about the Guide nut - where you see the red, that is where I had to trim out part of the thread that prevents the screw from fully advancing as the thread is being cut. If you do this, then you're creating the wood screw will be so much quicker than mine. Only thing you may have to fight is the depth of your router bit. If too deep, then the freshly screw will be loose in the guide nut. If not deep enough, the advancement of the screw will get nearly if not impossible to advance. If this is the case. STOP! Slowly advance the router down. I looked at the depth of the bit and compared it to the guide nut depth. I believe it should be nearly equal to what you have. If you are wanting to have the thread cut very close to the edge of your screw (as in the head of the screw) you'll need to remove the guide for the screw and just have what I have pictured here. I was very lucky and had it be tight enough to not rock around very much and loose enough to allow the screw to be advanced easily.
Now this photo I'm trying to show you the roughness of the nut, but now it looks better than I remember. Perhaps the threads of the nut burnished while I was creating the screw. The only issue I've had is that the depth of the tap wasn't deep enough - it should have gone at least one more time as I'm about a solid 1/64 if not 1/32th too deep, making the screw not quite the true 2-1/2" screw. But again, I'm trying to get perfection and this just won't matter. I don't think anyone is going to grab some calipers, measure my wood screw and give me a hard time that it isn't 2-1/2" screw.