There's problems inherent to the Sharpmaker system when using it to rebevel.
First of all, the rods aren't perfectly straight. One day you might use a slightly concave corner to rebevel, the next you might use the slightly convex corner and find that it takes 500 strokes to once again hit the edge.
Secondly, there is slight play in the rods and base. Pushing down hard on the rod will cause it to shift slightly towards the base (increasing the honing angle only when rebevelling with large force).
The third point is that there is also side-to-side (towards/away from the body) movement of the rod, especially when using lighter pressure on the rod such that it doesn't "stick" in the central position. Moving away from this position means that the honing angle has decreased.
These last two points mean that as one approaches the final edge finish, the honing angle becomes relatively smaller. It's rather difficult to remove large amounts of steel with the white rods or low pressure brown rods. The net effect of these factors is that after the initial rebevelling at 30 or 40 degrees (or higher depending on the amount of flex), subsequent attempts to match that angle with white rods or lower pressure will not be successful.
To Spyderco's credit, they suggest establishing the primary bevel at 30 degrees and cutting the secondary bevel at 40 degrees, just like how other forumites have advised in this thread. This would make the secondary bevel much easier to establish and work on. But I'm a difficult knife nut and I don't want a secondary bevel!
