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Micro fractures

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  • Micro fractures

    I'm a life long woodworker and retired high school shop teacher. I've never been great at carving nor sharpening. I've recently started carving on a semi serious level and have just finished about 150 of the "Larry Green designed Happy Christmas Trees" carvings. I've been really frustrated with my sharpening! I feel like I can put a great edge on a kitchen knife but when I sharpen my carving knives, I always end up with small chips/micro fractures on the cutting edges after a few minutes of carving.

    I use some re-purposed kitchen knives for my rough out knives (Kevin Coates style) and then I have Pheil and OCC detail knives (the OCC just arrived in my mail box yesterday so I have not sharpened it yet). I've found that the kitchen knives and Pheil seem to be the worse as opposed to the rather soft stainless steel of an old Rapala fillet knife.

    My sharpening is done on a Cerax 1000 grit stone followed by a quick pass on a leather belt on a 1" x 30" strip sander. While carving, I use a leather strop. I wonder if I'm getting too sharp an angle and the cutting edge is then breaking off?

    Any suggestions?
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  • #2
    Without looking at your knives, I'd guess your bevel is wrong. Can I assume you are stropping any wire edge off?

    I personally am in favor of a convex edge on my carving knives- supposedly the strongest edge you can put on a knife.. Lift the back edge of your knife slightly higher for the last pass on your stone, and roll the knife back down to the bevel. Do this on both sides, and push the knife down the stone like you were trying to slice a label off it.

    Proceed to your strop and see if it helps.

    I hope that was clear...

    Buffalo Bif


    • #3
      Most knives are manufactured to get through the initial sale and first use. Most knife users expect the knife to be immediately usable. I'm talking about kitchen and pocket knives. Carvers are very different. We need very sharp knives that can be maintained as very sharp. The steel chosen for some knives is not the best for our sharpening methods.
      I bought an attractive pocket knife a few years ago. I sharpened it the way I sharpen my carving tools, but it simply will not hold an edge! It doesn't chip off; it just goes dull. A steeper bevel holds up a little longer.
      The knives I use for carving are a different steel. They were sold as Pfeil chip carving knives. They rarely need more than a few strokes on a piece of cardboard charged with compound.


      • #4
        You have some good detail knives. Sharpining is a acquired skill and can take some time. As pallin said we all have our own favoret system. There are many youtubes on the subject. Your new OCC should have a good edge try to maintain the angle of the bevel on the cutting edge on your strop. Do not put a lot of pressure on the blade, let the strop and compound do the work. lift the blade off the strop or stone do not roll your wrist at the end of you stroke. When using the belt on you strip sander use a light touch in short times on both side checking often. keep some scrap to check your cutting edge. Stop when it gives you a smooth clean cut.The power strop well remove steel fast if you hold it to long the high rockwell steel can be britle if you get the edge to thin. Early on I had to regrind a number of tools because I made the bevel to thin. Do not take deep cuts with your detail knives, multiple shollow cuts are better and gives you better control. Hope this is helpful. Do not give up it will come tith time.
        Last edited by Claude; 01-25-2021, 02:39 PM. Reason: typo
        We live in the land of the free because of the brave!


        • #5
          Look at your knife edge under a very bright light. I have a nice LED lamp for this.
          If the edge is sharp, you can't really see it as there is nothing to reflect light.
          If the edge is chipped or more likely thin and folded over like an envelope flap,
          You will see obvious bright sparks of reflected light.

          One more diagnostic thing to try. I do this to judge the starting grit in a real sharpening job.
          Brian T


          • #6
            The only p[ower sharpener I use is Tomz (TOM Ellis) It is slow but you don't have to worry about burning your blade, All of my belt grinders turn too fast to try and sharpen a knife; to shape them they are ok, but you new to a slow action when getting the desired carving edge. Once I get a knife where I want the edge using my TomZ It is just strop time from then on Util it time to break out the TomZ.
            I've been thinkinf\g about making a basswood disk that could put groves and crests in, to use as power strop for Tom Ellis maching
            . . .JoeB


            • #7
              it sounds like you are not stropping the wire edge off. And you really shouldn't need to do anything other than stropping the OCCT knife unless the edge becomes damaged. It has been a while since I have did anything to my tools other than strop.
              'If it wasn't for caffeine, I wouldn't have any personality at all!"



              • #8
                If the edge is fracturing, it sounds like the knives where not tempered properly, and/or you have much too shallow a bevel for the wood you are cutting.

                Check that the total bevel angle is at least 15 degrees for soft woods and 20~25 degrees for harder woods. Consider adding a 1/16"+ wide secondary bevel if its sharper then that.

                If you can get the blade out, you might consider cooking it in your oven at 350 to 400 degrees Fahrenheit for about 30 minutes. Use a preheated oven to help reduce overshoot. Do this if it already has a steep bevel angle and you can't return the knife to the manufacturer. Higher temperatures will soften the steel more and increase its durability more up to a point, but I wouldn't go much past 425 fahrenheit on a wood carving knife. You can try again at higher temps if needed, but once you reach a peak temp you are stuck at that level of temper and lower temps won't harden it back any.
       Straight and curved wood carving knives