A convex secondary bevel using primitive means

S

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Apr 28, 2007
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The conventional wisdom seems to be that, absent a belt grinder, the path to convex secondary bevel nirvana lies through sandpaper supported by strips of mouse pads or leather.

Tonight, as I stared balefully at the decidedly non-sharp original v-ground secondary bevel on my HI CAK (kite mark), feeling little inspiration to put together a makeshift sandpaper strop, I thought that a pretty nice way to erase the shoulder would be to use my thumb pushing a small scrap of sandpaper.

The blade being so large, there was no trouble gripping the spine such that the thumb could exert good repeatable pressure on the power stroke (trailing direction) and hardly any pressure on the return stroke.

Working the blade with 400-ish sandpaper for half an hour, using just a few scraps of sandpaper, totally erased the former secondary bevel, the new bevel being nicely convex to the very edge but not particularly sharp.

However, subsequent to this process, it only took a few minutes on the strop to get the CAK to almost push cut paper, or indeed to push cut with a little bit of cheating. Perhaps some more stropping can get it to push cut reliably, but that's not in itself a goal as the CAK is after all a dedicated chopper.

In sum, I was impressed with how easy and relatively fast it was to convex the secondary bevel on so large a knife with just a few scraps of sandpaper and thumb pressure.
 
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I, too, have been staring at a dull Kuk, trying to decide what exactly to do about it. Thanks for the inspiration!
 
The traditional mousepad method doesn't seem to work as well on a Khuk because of the blade geometry and size makes it tricky. The solution I've found is to pick up a couple of 5-gallon paint stirrers from Home Depot. I glued a couple of pieces of craft foam to each side of the stick. Then I attach strips of sandpaper with spray adhesive. use these the same way you would a file. You get the benefits of the mousepad method in a much easier to control format.
 
The KnivesShipFree strop is similar to that, roughly 1.75" wide by 13" long including the handle. I found it worked well on the khuk, with the strop moving across a stationary khuk. A similar approach with sandpaper seems like it should work pretty well.

Doing this stuff by hand sure encourages you to build ambidextrous skills.
 
When I use the stir stick method, I find a good technique is from a sitting position, lay the blade on my knee for the one side and run the stick across the blade and off the edge. For the other side I hold the pommel in my left hand with the blade resting outward on my forearm and do the same.
 
The CAK got a serious workout today, including getting chopped into somewhat rocky ground after busting through splitting wood (work) and getting stabbed through the sheet metal of an old oven (fun).

Ended up with some tip compression, some edge rolling, and a few chips the largest being about 1mm^2. I got rid of all damage but the largest chip on a coarse DMT and proceeded to redo the convex secondary bevel.

This time around I grabbed a 1.25" diameter rubber hose, wrapped it with a layer of thick cloth, and a layer of sandpaper on top of that just held in place by hand. Worked very well, and a subsequent stropping of the main non-recurve section of the blade had that sucker push cutting paper.

It seems likely that striking small pebbles in the soil caused the chips, but I still wonder if that section of the blade wasn't a bit too hard. Should be exposing softer metal by removing the damage.. just hoping it won't be too soft too soon.
 
I always do each side of the blade with each hand. Edge facing out.

This way, I try to reach consistency of angle, but my left arm & hand is still not as good at holding consistent angle :)
 
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