How is my problem convex grind solved?

N

Naphtali

Joined
May 20, 2002
Messages
150
I've been struggling with my convex grind knife for almost a year. The blade is slightly more than .200 inch thick. Compared with my Morseth (Russell), circa 1980, grind begins much lower on the blade, which translates to a much stouter overall blade configuration. And the Morseth has a slight hollow grind, which translates to a blade significantly easier to keep sharp while it functions much better as a cutting tool than the convex grind blade.

Strop-sharpening on wet/dry sand paper atop a computer mouse pad should not be difficult. But it is nearly impossible. I am strongly considering having the convex grind altered to one similar to what is on my Morseth.

I have the impression that most knife makers who can do the job will not. As a rule, they do not work on another maker's knives. And, of course, my maker has passed away.

I don't want to "File 13" my problem knife. I welcome help and a solution.
 
Hello,

If i were you i would discard the mousepad and use a firmer backing like wooden backed leather to thin out and reduce the curvature, the mousepad is great if you like sharpening on a pillow but it is easy to add some nasty uncontrolled convexity and it is far from foolproof as a lot of people make you think.
 
It sounds like one seriously overbuilt edge. I would recommend ditching sandpaper entirely and switch to a hard stone (coarse silicon carbide) or a belt grinder. You will be removing too much steel for sandpaper to be a good choice - it will be constantly loading up and wearing out, and you would have to start with 60-80 grit.

You need to transition the existing "shoulder" way back into the face to thin it out properly, turning it into a true full convex and very nearly a full flat grind. By hand this is a project that will take several long sessions. Making a grid of Sharpie lines, or at least running them radially from spine to edge will allow you to concentrate your efforts better.

Until more meat is removed, you will be severely limited in how thin the terminal edge can be and the tool will not cut well. If explained clearly, I cannot imagine being unable to get someone to do this for you, though it can be done by hand - I've done a couple myself that were thick, overbuilt sabre grinds. By the time you are done, expect a very shallow convex to accommodate the .2 spine thickness, as mentioned almost a FFG.
 
+1 to ditching the mousepad entirely (forever), in favor of a much firmer or HARD backing (wood, glass, stone); I'd even avoid using leather at all, over the hard backing. The mousepad is way too soft for heavy grinding on a thick blade; it'll take forever, because the soft backing won't allow the abrasive to work nearly as aggressively as it could/should. The previously mentioned 'sharpening on a pillow' description is very apt, in describing it. With a very hard backing like glass, sandpaper can feel and even sound very much like a stone in use, and works much better than if used over a soft or conformable backing.

Wet/dry sandpaper on a hard backing like glass/stone can work reasonably well on relatively thick blades, if you don't have a good coarse stone; but, as mentioned, you might have to go through several sheets of it. As an alternative, an aluminum oxide or ceramic belt for a belt sander/grinder can work a bit more aggressively, as they're generally tougher (abrasive doesn't break down as fast as the SiC abrasive on wet/dry paper), and better ones will resist clogging a little better (but they still need to be cleaned periodically). Something like 120-grit or lower can work pretty well. The belt can be cut at the diagonal 'seam' where the ends are attached, and laid flat on a hard backing like hardwood, glass or stone; even better when gluing or attaching the belt to the hard backing. The extra length of the belt, when cut and laid flat, adds additional speed in the work, permitting long, sweeping strokes.


David
 
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I understand that using firm backing for stropping will allow the abrasive to work more aggressively. I am nearly certain that moving the amount of metal necessary ". . . to transition the existing "shoulder" way back into the face to thin it out properly . . ." is beyond my skill. Attempting to do it manually would result in "butchery" of an attractive knife. Were I to buy and use a grinder, I suspect that not only would butchery occur, but I would ruin the heat treat randomly.

But at least I'm getting a handle on what need be done. We still need to work on: How to do, and who to.
 
Naphtali said:
I understand that using firm backing for stropping will allow the abrasive to work more aggressively. I am nearly certain that moving the amount of metal necessary ". . . to transition the existing "shoulder" way back into the face to thin it out properly . . ." is beyond my skill. Attempting to do it manually would result in "butchery" of an attractive knife. Were I to buy and use a grinder, I suspect that not only would butchery occur, but I would ruin the heat treat randomly.

But at least I'm getting a handle on what need be done. We still need to work on: How to do, and who to.
Click to expand...

To me, the simplest approach would be to find a 'beater' blade of similar thickness and geometry (and steel type, if possible), and practice 'stropping' on fairly coarse-grit sandpaper (or the grinder belt as I described) over a hard backing. Glue the paper/belt to the hard backing, and just strop away. Don't worry about the cosmetics at all; just focus on the feel of it, and watch the effects on the edge as you work. You'll quickly get a feel for how the abrasive is working on the steel, and I bet you'll find it's not quite as intimidating as you might've assumed.


David
 
Naphtali said:
I understand that using firm backing for stropping will allow the abrasive to work more aggressively. I am nearly certain that moving the amount of metal necessary ". . . to transition the existing "shoulder" way back into the face to thin it out properly . . ." is beyond my skill. Attempting to do it manually would result in "butchery" of an attractive knife. Were I to buy and use a grinder, I suspect that not only would butchery occur, but I would ruin the heat treat randomly.

But at least I'm getting a handle on what need be done. We still need to work on: How to do, and who to.
Click to expand...

As per David - this operation is time consuming but not technically difficult. You can also buy some woodworking sandpaper - the tan Aluminum Oxide no load variety and glue that to a board etc. Use a hard wood shim and just practice shaping it into a full convex blade. The cosmetics can be dealt with as you go to finer abrasives, the real key is to have realistic expectations about how long it might take. The end result is going to be very rewarding and convert a tool you might never use again, into something you might use everyday.
 
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