Jeff :
<font face="Verdana, Arial" size="2">should I sharpen my Spydie Military in CPM-440V to 30 degrees or 40?</font>
The difference in cutting ability from 15 to 20 degrees per side will be significant and immediately felt the first time you cut anything. The question then becomes, at this level of acuteness does the edge have enough durability to resist chipping, impaction and deformation? That comes down to how the steel is heat treated, quality as well as particular cycles, as well as how you are using it and on what materials.
The heat treat part is relatively easy to process as the RC range is known that Spyderco uses, as is the quality of the heat treat - high. The RC is a little low for a light use knife, however it should easily be able to handle a 15 degree edge for most cutting work, even on harder materials.
The most critical part is how you are using it. Method can play a critical role, at least as much as, and sometimes even more so even than the materials being cut. Slow controlled cuts, with low twisting can be done on very hard materials even with thin edges on brittle steels without harm.
For example, I have a small knife from Lynn Griffith in ATS-34 that currently has a dual flat 9.5 degree edge bevel. I can cut 1mm copper wire, shielded cable, seperate poultry, and even cut up tin cans with no edge damage.
The critial part is that the cuts must be made in a controlled manner with a load perpendicular to the cut and *no* torques. In hard materials like these, if the edge experiences lateral forces it will snap. For example while I can slice cleanly through desk top class staples in a controlled cut, if I just do a hard rip into one, the staple will twist out of the cardboard, and in the process snap around the edge and chip it out. the damage will be sub-mm, just visible.
In regards to plastics, fabrics, flesh, cardboard, rope, wood, and similar materials, the edge will suffer no damage even if used with far less care. These materials are simply not hard enough to damage a quality blade even with a thin edge unless you are chopping of course.
Anyway, back to the Military. I would try a full fifteen degree edge. If you experience some damage, based on the RC I would assume deformation, then I would try putting a secondary edge bevel of 20 degrees over the 15 degree one once you steel the deformation out. Keep the secondary bevel small, it doesn't have to be as deep as the damage that you saw.
This dual edge profile, 15/20 degrees, is how Joe Talmadge has often described his edges. It is a compromise between the cutting ability of the 15 degree edge and the durability of the 20 degree one. Different people though cut different things in different ways, the only way to find the optimal edge level fo you is to basically keep lowering the edge until it takes damage, then you put a slightly more obtuse secondary edge bevel on and you are golden.
<font face="Verdana, Arial" size="2">If so, I would then want to go to a polished edge using stage 4 of the Sharpmaker</font>
I am not familiar with the stages of the Sharpmaker. However as for edge finish, it depends on what you tend to mostly do. For the highest performance in push cutting you want a very fine polish. However to slice harder materials you are better off with less polish. Both finishes however need well aligned and formed edges with no burr so the sharpening needs to be done with care for each case.
If you decide to alter the bevels, on the Military or other blades, I would be interested in how you make out after they have seen some use and would appreciate an email.
-Cliff
