Hi, I just aquired one of these with identical blades to yours - could you describe how you sharpened the blades exactly ?
I have a Renegade 250 with a 5 HP Briggs & Stratton engine that I bought new in the later 1980s. Mine has the square bolt-on hammer knives in the grinder-shredder section. See page 7, photo 9 in the Renegade 250 Owner's manual that is downloadable from this thread.
We used our machine extensively. What I found was the WW Grinder did not use very good steel for either the chipper knife nor the grinder hammer knives. After wasting much time swapping through a rotation of three chipper knives (bought as spare parts), and rotating the grinder knives to bring up a new sharp corner, I had three new chipper knives custom made from D2 chromium tool steel.
The knife making company, Messenger Knife Grinding of Portland, Oregon, makes knives for huge log pealing machines that make veneer, and big knives for paper making machines. These people knew something about knives, so I had them design new knives for the Renegade 250. Their advice was to heat treat and temper D2 tool steel so it would stay very sharp, but still be tough enough to survive impacts against the branches without chipping out the edge or cracking. The chemical content for D2 tool steel is 1.4 to 1.6 percent carbon, 0.60 manganese, 11.00 to 13.00 chromium, 0.30 nickel, 1.10 vanadium, and 0.70 to 1.20 molybdenum. Sorry, I can't remember the Rockwell hardness they chose. The knife blades they made for the chipper were a complete success, lasting at least five times longer between sharpenings. The old chipper knives would smoke instead of chip after less than an afternoon of work.
With such good results on the chipper side of the machine, I had MKG make a set of new square knives for the grinder section, also made from hardened D2 steel, but made from 5/16" instead of 1/4" stock. The thicker stock gave the grinder rotor more momentum to keep spinning and not bog down when too big a batch of branches was fed in. Since I only have a 5 HP engine, this was a bigger deal for me than for owners with 8 HP engines. Again, the new grinder knives stay sharp much longer. The extra spinning mass also did make a difference in how quickly the grinder bogs down and stalls.