Recently I purchased my first edge tool. It is a popular multi-edge tool, and I had no problem with it on my side edges, however I did have a problem on my base edges. To start, I set the angle to 1 degree which I knew was my current base edge angle, and using a file I ran the tool VERY lightly over the edge. Immediately I noticed that ptex (base) material was being removed along with metal filings. This concerned me, and eventually I realized what was happening. It's much easier to show with diagrams. Looking at the image below (angles exaggerated for clarity), you can see that 0.25 in of file is exposed from the "guide" (the part of the tool that rests on the side edge), while the actual base edge is only 0.1 in.
As you try to lower the tool into place, your goal is to have 3 surfaces of contact between board and tool: they are higlighted in red below. The problem becomes apparent... when the file is aligned with the base edge, and the guide is aligned with the side edge, there is a huge gap between the base and the "base guide" (the long part of the tool which should rest flush on the base).
What REALLY happens though is shown below. Since the tool cannot find 3 surfaces of contact, it rotates slightly and finds 3 POINTS
of contact. They are shown in red below.
Notice the file is ONLY contacting the vertex between the base and the base edge. This perfectly backs up my original observation of ptex being removed when I was attempting to file only my edge.
If you file for long enough like this, you will remove both ptex and metal, the image below shows what material will be removed.
The image below shows the tool finally able to sit flush, and the side effect I've called "vertex shift."
At this stage you will have made your base edge 3 times as long, and it is now 2/3 ptex and 1/3 metal. Is this a big deal? I don't know the answer to that question... which is one reason I'm making this post. Opinions please! :-)
Below there is one solution I came up with while working on my base edge, but it is not perfect:
If you don't insert the file all the way, it cannot reach the ptex. However, the original problem still remains, which is that you start off at a 3-point contact situation (though your ptex is now saved by the "gap"). However the tool is not sitting flush... the red lines below show that angle.
If you file for long enough though, just with the earlier case which ended in vertex shift, the tool will eventually be able to sit flush. However, there is a new side effect:
The red above shows the material removed with this solution. I've called this side effect "edge step."
So, which one above is worse? I believe my board now has edge step since I used my "solution 1" method. I cannot see the edge step, since it happens at a SUPER small scale with only a 1 degree angle. And while it may seem silly to be analyzing such tiny pieces of geometry... isn't that the whole concept behind edge tuning? That very small geometry changes, to a very small piece of metal, will totally change the way your board rides? And don't we use tools to do this because it IS too small to see what's happening with your naked eye? I am really curious to hear people's input on this, and I'm totally expecting more than one response suggesting that I am making a big deal out of nothing. I've run this by some knowledgeable people already who keep telling me something is wrong with my images, but they won't specify what. If there is a real problem with my analysis, I am more than happy to hear it. Or if the images are correct, but everyone agrees that neither side effect I've described is a big deal, then I'm more than happy to hear that too. But... it was disturbing to take a brand new tool, to a brand new board, with very light pressure, and the correct angle set, and notice that more ptex was being removed than metal. That is what motivated this whole thing... and it is somewhat telling that the analysis perfectly backs it up, with the "3 point contact" putting the file right on the ptex/metal vertex.
Incidentally, there is a second solution which I cannot implement without designing a new tool:
If the guide could move, so that less file were exposed, all of the problems above would disappear. I have purposely left the name of my tool out so as not to throw any manufacturers under the rug, but if there are any tools out that have a feature like the one I show above, or in general don't have the shortcomings that mine has, I would love to hear about it!