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A couple of likely issues that pop out to me....
1. The material.... Files are a really poor choice for knives, simply because for about the last 20 years, more and more files are case hardened. What this means is that the steel used to make the files is not fully hardenable, but rather some type of a cheaper, mild steel, that has been case hardened. Case hardened means that only a couple thousandths of the surface is hard. Once you grind past that super thin hard "case", you have a low carbon/non hardened material..... not a good thing as far as a cutting edge goes. Unless you KNOW the EXACT type of steel a given file is made of, it's just a gamble as to whether it's actually a high carbon steel....or it's case hardened.
Over the past 2-3 decades, nearly every industry has gone to what's known as "spec manufacturing".....meaning that engineers no longer call for a specific steel type to create a given item....but rather state what the item must do, and how long it must do it, then ask for it to be made of the cheapest material that will fulfill the mission, at the time of manufacture. Sounds crazy doesn't it? But that how things are done these days. An example is auto/truck springs. At one time it was a safe bet that ANY auto/truck spring would be either 5160 or 9260 steel.... these days there are no less than 19 different alloys that auto/truck springs are made of. Files fall into the same mold.... so you never know the steel type you're getting. In some cases it might be usable for blades, but for the large majority, modern files, will be case hardened.
2. Geometry..... The degree of angle ground on the blade and the edge(s), plays a huge part in how well, or how poorly a knife performs. The thinner/finer the blade and edge geometry, the less cutting resistance a blade exhibits. I would suspect that with a 1 X 30 grinder, there just enough power/control to get decent geometry on a blade.
The ONLY way that anyone creating blades can be certain if the end product will be usable or just a "KSO" (Knife shaped object) is to purchase new, known steel. Otherwise you can waste a lot of time on something that simply will never make a decent knife.
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