Did you heat treat them or just use the steel as-is?
When steel is overheated going into the quench, or when it was made really hot and not given a couple thermocycles (normalizing heats), the grain tends to be really big and coarse. This is an enemy of sharpness.
Something as thin as the fillet blade can be really hard to heat evenly without overheating parts. I don’t make fillet knives, so this suggestion is theory, not experience: try putting a length of black iron pipe in the forge and slowly bringing it up to hardening temperature. Hold your blade inside the pipe to get the blade heated much more evenly, minimizing the effects of hot spots in the forge.
I used to have a young man coming over to my shop to make knives. He was one of those who just didn’t want to learn from the voice of experience. He’d seen a lot of YouTube smiths, so figured he could tell me how to do it. Using my steel and my abrasives (so I know those factors are not different), he made blades that just wouldn’t sharpen. At least, not sharp enough. I didn’t get him to snap a blade, but I bet if he did it would be gnarly big grain. I’m fairly sure he skipped normalization and quenched too hot. I don’t know why a magnet doesn’t seem manly enough to some guys.
Of course, if you are going from the steel as-is, there’s the opposite issue. It may be too soft. I don’t know normal specs on bandsaw blades. I’ve heard the number Rc 45, but I have no clue whether that guy knew or was blowing smoke. Regardless, bandsaws have to really flex around their wheels and are generally not very hard. If you didn’t harden the blade, try normalizing it a couple times then hardening it in a light oil. I like cooking oil, but every smith seems to have a different favorite, so I don’t push my choice on others.
I hope this was helpful.
Patrick
