The Stock Removal Blade – Part 2 - continued
I use the 120-grit to smooth out the bevels and remove most of the deep scratches. The 120-grit belt does not have to be new, but if it is too worn it will just heat up the steel without removing sufficient material. I have discovered that trying to use belts for too long just to save a few bucks is not worth it and costs more in the long run in mistakes, aggravation and wasted time. The 120-grit belt is called a "J" weight belt and is very flexible. By adjusting my tracking I can run the belt off of one side of the platen or the other. This allows me to bend the belt around the edge and clean up the plunge line while grinding out the deep scratches left by the 50-grit belt. I can also move the plunge cuts toward the rear to get them into alignment. It takes a little practice to know exactly how much of the belt to run off the platen. Too much and you can ruin the plunge cut. Too little and you cannot form the plunge and round it on the grinder, which can make it difficult to clean up by hand.
I put a new 220-grit “J” weight belt on the grinder and remove the masking tape. I slow the grinder to about 20 or 30 percent to reduce heat buildup and to have much better control over the grind. Any truing of the blade along the spine or edge needs to be done at this point. If the taper is not quite even I use the 220-grit belt to correct it. The same goes for the edge thickness. Finer belts cannot make major corrections and are primarily for finish purposes.
Now I switch to a 320-grit belt and slow the grinder way down and give some final attention to the plunge cuts. I like them nicely rounded with a smooth flow from ricasso to bevel. I do not worry about the 220-grit grind on the bevels at this time. When the plunge cuts are nice, smooth and even, I switch to another platen on which I have glued a piece of leather. The reason is that when using thin belts the lap joint on the belt tends to "bounce" on the platen leaving small divots in the steel. The leather removes the bounce and allows me to get a very smooth finish. While the leather platen is installed I start to form my convex edge. For me it is easier to grind the edge as a succession of angles and then blend them together with the slack belt technique described by Terry Primos. I make several passes along each side of the blade and start my convex geometry about ¼ “ - 3/8" behind the edge, holding the edge up and the spine of the blade further away from the platen for each pass. When both sides are pretty even I blend them with the slack belt behind the upper roller wheel on the platen. I get the steel very thin at this point, but try and keep it close to .015 - .030 so that it can withstand the thermal shock of the hardening quench without cracking. When I am satisfied with the edge configuration I make a few more passes on the bevels to remove any scratches that may have occurred when working on the edge.
We have to do a little handwork now. I use 320-grit wet/dry sand paper and sand each side from the ricasso to the tip. I take special care to clean the plunge cuts and check for scratches there and on the bevels. Once you start sanding in the lateral direction any deep scratches will show up immediately. They are a lot easier to get out now when the steel is fully annealed than they will be later after hardening. Very occasionally I will have to go back to 220-grit to grind out a really deep scratch, forcing me to repeat the 320-grit step as well. I usually have to do a little final blending of the convex edge at the ricasso and tip where I was being real careful with the grinder to prevent mistakes. For small areas it is fast and easy to switch from 220 to 320-grit if heavy sanding is needed for final blends and cleanup. When both sides are sanded I give the blade a final inspection looking for scratches, straightness, even grinds, etc. The blade looks very close to the finished product by this time. We are now ready for the thermal treatments and testing.