Originally Posted by Bob Nash on Oct 22, 2014
This is a question I see a lot on forums and get asked a lot by customers while in the shop as well as at shows. This can happen on any of the guided systems out there and depending on the system some of the causes I address here won't apply or will be a variation on the theme.
Let's look at if the bevels are uneven left to right which is what is generally what people are concerned about when they ask this question as opposed to being uneven heel to tip. In my experience there are at least three or four basic causes for these uneven bevels.
#1 that the initial work on the knife is not done evenly. We've all probably done this at least once while learning and be shocked at some point in the process to find the knife not looking the way we hoped. Basically people will grind away only on one side of the knife until they raise the burr from that side. Then when they get it raised on that first side they go to the other side and bring up the burr from the second side. Since it doesn't take as long on the second side they won't do as much work on that side as they did on the other. The result is that they will have pushed the edge off center - farther from the first side and closer to the second side. This of course makes a wider bevel on the first side and smaller bevel on the other. On the Wicked Edge the bigger one is usually on the right since more people are right handed and start on that side first
For the remainder of the reasons I think it is important to understand that you need to distinguish what the angles you are sharpening at are measured relative to. The angles marked on the sharpener are relative to some particular knife edge location, with an angle cube the angles you measure are relative to whatever surface you zero the gauge to, and then there is the angles relative to the actual cutting edge which is the important set of angles since this is the angle you are truly sharpening at. So if the knife edge deviates from the particular edge location that the sharpener is marked to the angle actual sharpening angle relative to the cutting edge will vary accordingly. Similarly if the angle gauge is zeroed to the base and the knife isn't at 90 degrees to the base then the angles will vary from what the cube reads.
#2 is that the knife from the factory actually has the cutting edge off center. This is fairly common in my sharpening experience at shows especially with less expensive knives. Upon examination the bevels will look even left to right but when you match the angles using a sharpie you will find that one angle will be bigger and one smaller. So if you set the angles equal on the sharpener using the base rod markings or equal using an angle cube you'll then be on the shoulder on the side the edge is farthest from and on the other side you either won't be or won't be as dramatically. So when you work, assuming you keep your work even, you'll push back the shoulder on one side farther making the angles equal on the knife but the bevels uneven. This could happen on either side of the knife depending on what direction it was off center to start with.
#3 is that the knife is tipped to one side, generally on the Wicked Edge this tilt is to the left because of how the vise works. This can happen with any knife that doesn't have good parallel faces for the clamp to grab onto, and it is possible that the knife will lean either way, again left being most common. If the knife is tipped one way or the other then the angles, though equal on the sharpener, won't be equal relative to the cutting edge, the side it is tipped toward will have a larger angle so a smaller bevel and the side it is tipped away from will have a smaller angle so a wider bevel.
#4 is the thickness of the knife. So for most pocket carries and kitchen knives etc this is not an issue as the angle variance on the Wicked Edge is very small - say around a tenth of an inch or less in thickness. As the stock gets thicker though, since the left side of the vise on the Wicked Edge is fixed in place, the center of the knife moves farther and farther to the right. Thus the angle on the left gets larger and the angle on the right gets smaller giving you a bigger bevel on the right and smaller on the left.
And of course it is possible for it to be a combination of these causes which could accentuate or ameliorate the situation depending on how they line up.
I think that the easiest solution to all of these but the first one (which is solved just by making sure to keep your work even) is to start by finding the angle on any knife using a sharpie marker. I show this technique in our video on finding the sweet spot
The key is that the sharpie shows you where the stones are hitting on the knife no matter how it is oriented so you can adjust the angle to compensate for the above issues. If you want to reprofile, once you find the existing angles that match, just move both sides in or out by an equal amount. So if I find the settings on the base rod to be 19 on one side and 21 on the other and I want to come to 17 you can bring in both by 2 degrees as marked.
If you prefer to use an angle gauge to set your angles then what I do is one of two things.
First is my personal preference: find the existing angles as told to you by the sharpie. Then if possible zero you cube to the knife and measure your angles against that. When you set your angles equal you'll then know if you are moving the angle more on one side or the other, and the side you move the least is the side you need to do extra work on to keep the bevels even as you set the new angles on the knife. And if you move them equally then you can just keep your work even. With the Pro Pack II arms I measure the amount moved in or out in turns of the micro adjustments and number of degrees on the base rod.
The other method is to set the angles with the gauge and then test with a sharpie before you get to work to see where you are hitting with the stones to decide which side will need more work if either.
In either case you need to keep an eye on your bevel widths as you work to make sure you aren't making one larger than the other.
And with #3, you'll want to shim the knife and use the sharpie in combination (or zero the angle gauge to the blade). There are multiple ways to shim it, but the one I find easiest is to wrap the spine of the knife with a small square of chamois as in the video above (or if it is double sided around the side that is in the clamp). Then first make sure that your lower vise screw is retracted all the way so that the vise can come together at the bottom. Now tighten the top screw to hold the knife in place and then while looking down at the knife from above tighten the bottom screw to clamp the knife. Watch for the knife to tilt as you tighten and if it does, twist it back straight up while you continue to tighten. When you have the clamp tightened it shouldn't move. Your goal in retracting the lower vise screw is to get the gap between the two vise halves to be about equal from top to bottom. If the gap is more equal then there isn't as much pressure to tip the knife to the left. Watch for the knife to tip as you work too
Hope that helps