I think it might be worthwhile analyzing one (or more) of your failed knives. I assume you bought them new (sharp) and then used used them some; when you went to get them sharp again they didn't live up to snuff. I would also need to assume you are using double-hollow ground knives?
First, I'd practice on the "cheaper" knives which are also a little easier to get sharp—at least for a bit—then move up to the harder ones (if you want) which take a bit more finesse sometimes—also a bit less damage to the pocketbook if you do mess up
(which can also be easlier if you start getting aggressive).
I do find that some times I just to better than others, too, or things don't last as long, so I am by no means the expert, but I've gotten better at not having it be as expensive. So I use a cheaper (Chiarugi, about $40) for the roughing out. I use and older Landwell H for the next pass, a Jenda 15k for the fine tip work, and a NOS original Herder for texturizing the back. The last two are either pricey or mostly irreplacable so I try to avoid aggressive sharpening unless unavoidable (and so far for the last 6 months or so, I've only maybe done it once on the Jenda and not on the Herder).
That said, do you know if your problem is that the edge isn't sharp enough, or, as beseals hinted, that the burr might not be set at the right angle? If you try to use the knife at a different angle i.e. tilted other than perpendicular to the cane surface) does it help? If that is the case, you probably just have the burr set wrong (usually, in my case, too steep—which I think would also be caused by sharpening at too steep an angle). If that seems to be your major issue, then try using just a burnishing rod to reset the angle of the bur. That doesn't take off any (significant) metal, so, as long as the edge is thin enough, you can adjust the burr's angle a bit without taking off more metal (and potentially ruining an edge that was perfectly thin but bent wrong). Using a burnishing rod (or equivalent—see below) also is good when the knife first seems to be not sharp enough—often the burr has just gotten bent a bit).
You don't need to go out and get an actual burnishing rod for now unless you're just hot to get one. My last teacher said she'd used a stand post in a pinch. I use the back of an old RDG Swiss beveled knife (the knife itself is long gone) which is nice and rounded and very smoothly polished.
I've switched about a year ago to grenadilla plaques, as well. If you're a flat-plaque-only afficianado, I don't know if they make flat grenadilla plaques. I've heard (apparently originally from David Weiss) that a thin guitar pick is a good plaque. The metal ones do chew up the knife—I've gone through two grenadilla plaques in the last 6 months (not totally gone, but the edges chipped more than I like), which tells me how much was being done to the knife instead before.
My current rule of thumb is to not use the diamond more than once a month, and preferably only 2-4 times a year, on the expensive knives (should you decide they are worth it for you). At some point, you will have no choice.
I have found the Landwell book to to be helpful, although I use stones more like the Jende recommends (a 15k for touchups,
a 5k (equivalent) for more agresssive work, and, ultimately an extra fine diamond when I have to (see above).
The obvious question to ask yourself is what is different from before when you had no problem, and are you sure it's you? Have you tried different types of knives? I had pretty good luck with the first Landwell H I used, but have not had good consistent results since than, and read a lot about how people complained about spotty quality in later versions, although, to be fair, those complaints were dated prior to my first (good) experience. Then again, I was pretty aggressive with the diamond in those days, which kept it sharp while it lasted, but it was pretty thin by the time I was done with it.
I have had some luck, at least to the point of getting a "traveling" knife from an old Landwell H I'd thought long past use by using a torch per Jonathan Marzluf's post elsewhere on this blog (don't have the exact reference at this point).-kby
Last edited by kby (2014-12-26 02:16:06)