The best lessons are learned from experience.
I understand sentimentality and wanting follow in the steps of your grandfather.
HOWEVER, depending on the type (and age) of the planer blades, chances are very good that you're looking for a "cheap" AND "useable" knife, you're just wasting your time, and ironically, any money you were trying to save in the process.
As several others have already tried to tell you, you can buy several feet of a known steel that will be MUCH easier to work with, heat treat, and get a decent knife out of, with what ever money you will end up spending on new grinding/cut off wheels, and the dozens of sheets of sand paper you're going to burn through trying to mirror polish hardened M2, D2, or whatever it is you think you have.
If you must continue your efforts on the planer blades, understand that they are currently tempered quite hard (and brittle). That said, a lot of that temper will likely be removed as you attempt to grind/cut your profile and bevels in its hardened state. Theoretically you could anneal the stock, drill, shape, grinder, finish etc... the steel, and then re-harden and temper it, but tool steels typically require fairly precise heating, ramp and soak times, and usually in an oxygen free environment.
Now, some makers do work steels like this hard and then draw the temper back to a useable "knife" hardness, but this involves quality grinding belts on a decent grinder, carbide drill bits, and a heat treat oven to precisely temper the blades. (Your kitchen oven won't get nearly hot enough)
You can of course get it "so so" with angle grinders and loads of sand paper, and possibly even get an edge worked up, but it likely won't sharpen very easily or consistently, and the edge holding will be dubious. At the end of the day, only you can decide what your time and effort is worth. You will already know what grinding wheels and sand paper cost.
Good luck!
if you insist ...