The Stock Removal Blade - Part 3 - continued
I temper three times, cooling for 30 minutes between cycles. The first cycle is for two hours at 350 F. The second and third are one hour at the same temperature. I use the kitchen oven and a high quality industrial thermometer. I turn on the oven before beginning the quench cycle and by the time I am ready to temper the oven temperature has stabilized. IMPORTANT NOTE: Failure to obtain permission from the spousal unit before tempering in the kitchen oven can have dramatic effects on your general health and well being!
I usually do my tempering late in the afternoon and early evening then put the knife in the freezer after the last cycle. Our freezer holds a constant 0 F. Testing seems to indicate that I get a very slight improvement in edge retention over blades that have not been frozen. I am still testing the freeze process. When the knife comes out of the oven for the last time is has a nice light gold color.
I used to be of the opinion, because my results were very consistent, that I only needed to test every 10th or 12th blade. I decided that this was not right and my customers deserved better. Terry Primos and Ed Caffrey get a lot of credit here since I admired their dedication to quality and commitment to each customer on every blade. I clean up the blade on the leather platen then take 400-grit belt to put on a good convex edge and polish with an 800-grit belt. I lightly buff the edge with some white buffing compound then strop it on leather loaded with the same compound until it is hair shaving sharp. I like to vary my tests and am often guided by what I have around. Sometimes I will cut manila or sisal rope if available. I usually have a lot of cardboard to cut up, which is a great test. I sometimes will chop a few boards or limbs, especially for larger knifes like fighters or Bowies. However, one I always do is the brass-rod, edge-flex test. I have found that for my knives this test is a good indicator of the blade quality. Ed Caffrey gives an excellent description of the process here:
Testing Knives. . .. I have included a photograph of my test using a copper rod since I ran out of brass. If you look carefully you can see a slight deflection in the edge.
If the edge does not pass it must either be tempered at a slightly higher temperature or rehardened and the whole thermal process repeated with the tempering cycle set to a lower temperature. I also do periodic destruction testing for two reasons: to see how much abuse a knife can take and to look at the grain of the steel. Again, so as not to be repetitive, please see Terry's post for additional photographs and testing descriptions. For this test I cut some newsprint, chopped some wood and then shaved the hair. The final picture shows a close-up of the blade edge after testing. There are no chips, deflections, flat spots, etc.
The blade passed and is ready for a hand finish. The first thing I do is gently stone or grind off the edge of the blade with a very fine belt, just enough to dull it. I never do finish or assembly with a sharp knife. Next, I hollow grind the handle. This lightens the knife considerably and leaves a nice cavity for the adhesive when I bond the handles. It also makes it much easier to do the final flat sanding due to the smaller surface area. I use the small-wheel attachment with a 1.25” wheel and a slightly worn 50-grit belt.
I will use the Bader and a new 400-grit belt and the leather-covered platen to do the final cleaning of the bevels, then switch to hand sanding. With all of the preparation done before heat treatment and the belt cleanup, I usually only have to use one or two grits to finish a knife. I finish my knives to 400-grit, with a few additional passes using 600-grit paper to make the lines look clean and smooth. When done with the Bader I put the knife in the knife vice for hand finishing. The knife vice is by Rick Leeson, owner of Custer Forge and Welding. He also built my forge.
Custer Forge and Welding.
All of my finishes are longitudinal, from ricasso to tip. For the final finish I use oil or Windex. Don't laugh, Windex really works as a cutting fluid! Engnath has a great description on his site. Select the "Handsanding" choice for a detailed lesson on hand finishing. There are some great diagrams that show the process. I pay particular attention to the plunge area and the area of the ricasso that will be visible between the handle and the plunge, once the handle is in place. The blade is almost ready. Notice that there are still a few scratches in the blade. I will sand these out, make sure the handle is flat, and when all of the scratches are out and the blade looks right, I wipe it with WD-40, dry it off and wrap it with masking tape from ricasso to tip to protect the finish during handle assembly. Unfortunately, I have found that in my damp NW environment I would occasionally get rust on the blade between finishing and handle installation if I get delayed for any reason. The WD-40 seems to work well for preventing the rust.