Newbie question on using belt sander to sharpen kitchen knives

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kmcdonou

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Mar 16, 2012
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I just started to use a Kalamazoo belt sander for sharpening my kitchen knives with the goal of getting functionally sharp knives. I started out with a Trizact A45 belt (400 grit). I passed the knife a 2-5 times on each side, which was enough to raise a burr. I then put on the leather belt and applied green compound. I ran the knife across the belt 2-4 times on each side. The knife edge, although smooth, wasn't really sharp. What am I doing wrong?

My angle of the blade against both belts seemed to be consistent. Should I have run the blade more times on the A45 belt? I always thought that once the burr was raised I could go to the leather belt. Did I need more times on the leather belt?

Any help would be appreciated.
 
You're not removing the wire edge properly it sounds like. Before going to the leather belt/green compound try running the edge through some cardboard to remove the wire edge. The green compound will likely then be sufficient to bring the edge back to proper apexity.
 
Use a very soft touch with the leather belt. It is very easy to 'round' the apex a bit - the very cutting edge will have an edge geometry so broad that it won't cut well eve if it can shave hair off your arm. Coming off the belt try backdragging the edge at a larger angle along a wooden bench, dowel, cutting board etc to make the burr stand extra proud and give it a final pass on the 400 grit belt. Then go to the leather at a slighter lower angle with very little pressure - very easy to sink the edge a bit, generally belts have less give than leather. I agree w/ 42 Blades - the issue probably has something to do with the burr/wire edge. Another consideration is that many common kitchen knives have relatively soft steel and may have been ground rather slapdash. You might have to remove a touch more steel along the apex to get to material that hasn't been overheated from a poorly managed factory grind.

As a general rule, whether working with a powered belt or bench stones you should remove as much of the burr as possible with the fixed abrasive (stone/belt/sandpaper/diamond plate) before moving on to the "stropping" phase. Be honest with yourself - extra effort pays large dividends when you switch to a loose abrasive on a leather belt - shortcuts seldom pay off. Also - allow for some time to get familiar with the equipment. A 400 grit belt followed by a CrO on leather can yield some top-notch results. Stop and observe often.
 
I use two 400 grit belts. First, a newer one to remove metal to the apex, then an old smooth belt to finish and remove the burr. Keep your angles the same on each belt with slightly more pressure on the old belt, and be sure to use an eraser on the old belt to expose some grit. Then the green leather belt with very light pressure to polish the edge. After that my buffer doesn't have much to do.
 
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Those are great ideas. I will work on these techniques and see how it turns out. Thank you.
 
Although this is an old thread, I wanted to ask some more questions. I've refined my technique since originally posting. My initial problem was that I was using too steep of a sharpening angle. Once I figured out the angle, and was able to consistently hold it while drawing the blade across the belt on both sides, I was able to get sharp knives.

I have a question about using the leather belt. It seems this belt flops around more than my other belts. Is this something I should worry about? I am concerned that if it doesn't run fairly flat it won't sharpen consistently and will be more apt to dull my blade. I haven't found that to be true yet, but am wondering does the flap get worse as the belt ages? I am using the leather belt on a Kalamazoo belt sander.
 
I use a leather belt too. Make sure you remove it after each use. Leather is going to stretch. Mine is very floppy but doesn't seem to affect its capabilities. I bought this one from edgemasters, got three from Lee valley and they all snapped at the seam.
Seems they all will stretch and become floppy.
 
If it becomes too loose you can always shorten it. Look at the original glued seam and duplicate the angle when making the cut to shorten it. I use Barge cement and prefer to replace the original glued seam rather than making a second weak point. Skive and/or sand to make a smooth joint.
 
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