Chasing the Edge..... :-(

[Cushing H.]

I usually have no problems with digging into the edge while grinding .... but recently I have been working on some new thinner stock (~0.07" 26C3), and the last few blades I have had some issues with starting to dig into the edge. I've been able to more or less deal with it .... but on the blade I was working on this afternoon (one of my 6" tomato knife variations) I had a LOT of problems with it. It started digging in about the middle of the edge .... so I just kind of sighed and completed the grind (FFG) and then went to re-profile the edge to remove the concavity. This of course then leaves a slightly thicker edge thickness, especially towards the tip of the knife .... so I started working (carefully) to re-grind the bevel towards the edge to bring down the edge thickness there. Sure enough, as I was doing this that same area that had the edge chewed showed loss of edge again I swear, I was looking and never saw the belt touch that area of the edge (just the flat of the bevel behind it).

Rinse and repeat.

Instead of completely destroying the blade, I basically gave up and salvaged the blade with a non-flat grind but reasonably intact edge .... this knife is for my own use, so I can deal with it. (picture below)

The edge is to the right in this photo. You can see the bevel towards the tip of the knife (top of photo) with three separate bevels. Like I said, every time I tried to reduce that to a single bevel that edge towards the bottom right of the photo would get chewed.

For people who have played a lot with thinner stock (like this 0.07" stock) .... do you tend to run in to this issue more often than with thicker stock???? Most of the other blades I have made have 0.09", 0.1" or 0.12" stock ... and with those I have never had this problem. Two explanations I can think of: 1) I am loosing my coordination (even though as I go I continue to feel like I have more control of the grind and the contact area between belt and blade), or 2) with this thinner stock the angle of the bevel is that much more steep, and unevenness in the grit of the belt will bring just enough "stand out" pieces of grit into contact with the edge, even though my main contact between belt and bevel is below the edge.

I have not done the specific math - but from the trig I do know that as the stock gets thinner, if a FFG is maintained, the angle of the grind goes down *fast*. Makes me wonder whether with this thinner stock al;ways doing a FFG is maybe something to be avoided???

 

[REK Knives]

I'm having a hard time understanding exactly what you mean - do you have any pics of what it looked like when it was chewed up?

You think it has something to do with the blade flexing around the platen when pushing it into the belt?

 

[Cushing H.]

I'm having a hard time understanding exactly what you mean - do you have any pics of what it looked like when it was chewed up?

You think it has something to do with the blade flexing around the platen when pushing it into the belt?

No photos I am afraid .... but what I mean is that the edge itself was ground, causing it to recede and creating a concavity in the profile of the edge instead of the continuous convex shape it was designed with...

 

[REK Knives]

No photos I am afraid .... but what I mean is that the edge itself was ground, causing it to recede and creating a concavity in the profile of the edge instead of the continuous convex shape it was designed with...

Ahh yeah I gotcha. I definitely think you're onto something with your point #2 above... What grit were you using? Also were you using any layout fluid or sharpie? Sometimes this helps me diagnose problems

 

[Dominick Maone]

May not be heat treated properly in that area. And the belts are wearing it down faster than surrounding areas.

 

[Cushing H.]

Ahh yeah I gotcha. I definitely think you're onto something with your point #2 above... What grit were you using? Also were you using any layout fluid or sharpie? Sometimes this helps me diagnose problems

60 grit … which is what made me wonder about point #2. I do always use layout fluid on the bevel as I grind them. Nothing unusual noted in walking the grind back towards the spine…

 

[Cushing H.]

May not be heat treated properly in that area. And the belts are wearing it down faster than surrounding areas.

Possible . But I did not do the HT, it was sent out.

 

[Natlek]

I usually have no problems with digging into the edge while grinding .... but recently I have been working on some new thinner stock (~0.07" 26C3), and the last few blades I have had some issues with starting to dig into the edge. I've been able to more or less deal with it .... but on the blade I was working on this afternoon (one of my 6" tomato knife variations) I had a LOT of problems with it. It started digging in about the middle of the edge .... so I just kind of sighed and completed the grind (FFG) and then went to re-profile the edge to remove the concavity. This of course then leaves a slightly thicker edge thickness, especially towards the tip of the knife .... so I started working (carefully) to re-grind the bevel towards the edge to bring down the edge thickness there. Sure enough, as I was doing this that same area that had the edge chewed showed loss of edge again I swear, I was looking and never saw the belt touch that area of the edge (just the flat of the bevel behind it).

Rinse and repeat.

Instead of completely destroying the blade, I basically gave up and salvaged the blade with a non-flat grind but reasonably intact edge .... this knife is for my own use, so I can deal with it. (picture below)
View attachment 1786452
The edge is to the right in this photo. You can see the bevel towards the tip of the knife (top of photo) with three separate bevels. Like I said, every time I tried to reduce that to a single bevel that edge towards the bottom right of the photo would get chewed.

For people who have played a lot with thinner stock (like this 0.07" stock) .... do you tend to run in to this issue more often than with thicker stock???? Most of the other blades I have made have 0.09", 0.1" or 0.12" stock ... and with those I have never had this problem. Two explanations I can think of: 1) I am loosing my coordination (even though as I go I continue to feel like I have more control of the grind and the contact area between belt and blade), or 2) with this thinner stock the angle of the bevel is that much more steep, and unevenness in the grit of the belt will bring just enough "stand out" pieces of grit into contact with the edge, even though my main contact between belt and bevel is below the edge.

I have not done the specific math - but from the trig I do know that as the stock gets thinner, if a FFG is maintained, the angle of the grind goes down *fast*. Makes me wonder whether with this thinner stock al;ways doing a FFG is maybe something to be avoided???

 

[Justin W]

When you have the edge all the way down to 0 tbe, on thin stock especially, almost any contact at the edge will eat steel. Its like it pulls the burr down with the belt. I stop around 10 thou at 60, then go to A300 trizact (80 grit), and just cleaning up scratches puts it in the perfect 5-7 thou before hand sanding. No belt finishing for me yet, too much speed.

 

[Cushing H.]

When you have the edge all the way down to 0 tbe, on thin stock especially, almost any contact at the edge will eat steel. Its like it pulls the burr down with the belt. I stop around 10 thou at 60, then go to A300 trizact (80 grit), and just cleaning up scratches puts it in the perfect 5-7 thou before hand sanding. No belt finishing for me yet, too much speed.

That description of pulling the burr down seems like a good description of what I experienced. I was at about ten mil when this occurred …. Probably I need to stop at even a little thicker … at least for now.

Interesting that thin stock behaves differently…

 

[Nick-D]

I just finish ground a long fillet knife out of super thin nitro v and had the same issue. I think it was flexing creating unever pressyre/contact. I glued a bit o timber to the back to hold and help stop. The flex, seemed to work for me

 

[Cushing H.]

I just finish ground a long fillet knife out of super thin nitro v and had the same issue. I think it was flexing creating unever pressyre/contact. I glued a bit o timber to the back to hold and help stop. The flex, seemed to work for me

Hmmm…. I remember seeing a video of a japanese blade smith who was holding the blade in some kind of wooden block with the blade held in place by some kind of wooden pin arrangement (not glued). I wonder if that would serve the same purpose? Not sure however how to create that holding block …

 

[Justin W]

I just finish ground a long fillet knife out of super thin nitro v and had the same issue. I think it was flexing creating unever pressyre/contact. I glued a bit o timber to the back to hold and help stop. The flex, seemed to work for me

Yep, it could be flex, or warp. Along the same lines, I use a simple jig when doing my initial grinding at 36 and 60 grit. I got some 1.5" aluminum angle stock, and just clamp my steel to it. After I have it ground "close enough" I switch to freehand and change my grinding direction from perpendicular to the blade, to 45° ish with the trizact. The trizact isn't as aggressive, and is more forgiving of little mistakes. I stop when I erase all the perpendicular scratches, and have the desired tbe.

 

[Stacy E. Apelt - Bladesmith]

My friend, Don, makes a grinding board for every blade. He uses plain 3/4" thick lumber. It is cut out to roughly match the blade shape. He bolts the blade to the block through the tang holes, grinds the board back to the blade profile, then grinds the bevels. He moves the blade over to the other side of the board and re-bolts it for the other bevel. After HT, the same board is used to finish the blade. The board and blade stay together from the start until the blade is fully polished. This eliminated warps or grinding issues.
He keeps the boards in a couple of drywall buckets for future blades and uses them for grinding templates for the next similar blade. He drills the tang holes in the bar stock and grinds the stock back to the board edges. Then he proceeds to grind the bevels.

 

[Cushing H.]

My friend, Don, makes a grinding board for every blade. He uses plain 3/4" thick lumber. It is cut out to roughly match the blade shape. He bolts the blade to the block through the tang holes, grinds the board back to the blade profile, then grinds the bevels. He moves the blade over to the other side of the board and re-bolts it for the other bevel. After HT, the same board is used to finish the blade. The board and blade stay together from the start until the blade is fully polished. This eliminated warps or grinding issues.
He keeps the boards in a couple of drywall buckets for future blades and uses them for grinding templates for the next similar blade. He drills the tang holes in the bar stock and grinds the stock back to the board edges. Then he proceeds to grind the bevels.

Now *that* is an interesting idea. It would also help with this mysterious loss of fingernails I continue to experience .

I wonder about being able to sense/deal with heating of the blade post HT (I still don’t have a misting system), but then again the wet board itself I suppose will help absorb heat…

Also it might be a little more difficult with Wa style tangs … but no reason you can’t start with a wider tang (with holes) and grind it to final shape after grinding the bevels? (I’m always tweaking it a little anyway…)

Thanks Stacy !

 

[Taz]

I use a piece of aluminum channel I hold along the tang and backside of the blade when grinding thin knives. The blade will flex away from the platen when using more pressure and more or less flex will change the bevel. I have felt a blade flex along the length of the blade as well as edge to spine of the blade when they are really thin, too. The aluminum channel seems to help keep it straighter. I will often use a S2-32 hard felt piece on a flat platen to blend the bevels and do belt finishing with very thin blades, too. Just gotta be careful near the edge since it will give a very slight convex to it and may bring it down to a foil thin edge that crumbles if you go too far with it.

 

[Cushing H.]

I use a piece of aluminum channel I hold along the tang and backside of the blade when grinding thin knives. The blade will flex away from the platen when using more pressure and more or less flex will change the bevel. I have felt a blade flex along the length of the blade as well as edge to spine of the blade when they are really thin, too. The aluminum channel seems to help keep it straighter. I will often use a S2-32 hard felt piece on a flat platen to blend the bevels and do belt finishing with very thin blades, too. Just gotta be careful near the edge since it will give a very slight convex to it and may bring it down to a foil thin edge that crumbles if you go too far with it.

This is all great … I suspect this backing board/aluminum idea will also help a lot with dealing with the tip area of very long knives. I’m finished grinding for a while (need to start on handles), but will definitely need to keep all this in mind…

 

[Taz]

Yeah, I tried getting the tips of fillet knives more flexible, but ended up with a dip in the spine around 2" back from the tip, so the spine was good thickness, then dipped down around 2" from the tip, came back up and then tapered down again to the point. The aluminum piece helped a lot with grinding super thin blades to support the back side so the steel would stay straighter through the process.

 

[Natlek]

My friend, Don, makes a grinding board for every blade. He uses plain 3/4" thick lumber. It is cut out to roughly match the blade shape. He bolts the blade to the block through the tang holes, grinds the board back to the blade profile, then grinds the bevels. He moves the blade over to the other side of the board and re-bolts it for the other bevel. After HT, the same board is used to finish the blade. The board and blade stay together from the start until the blade is fully polished. This eliminated warps or grinding issues.
He keeps the boards in a couple of drywall buckets for future blades and uses them for grinding templates for the next similar blade. He drills the tang holes in the bar stock and grinds the stock back to the board edges. Then he proceeds to grind the bevels.

Simply put, grinding jig solve all the problem when you grind thin, wide and long blade .
In fact I would like to watch a video of someone / there are those who claim to do so / how they grind FF bevels on 1.5mm thick Chef kitchen knife free hand ...............

 

[Taz]

Jigs don't always help. With a distal taper, the tip is still unsupported and can flex, but it will flex until it hits the back of the jig and then stops. And the blade can still flex spine to edge, too. Or if the blade is past the end of the jig, it doesn't help at all since the blade is flexing with nothing behind it. With a blade that is thin to begin with, the ledge has to be thin as well or the belt will grind the ledge as well as the blade, especially when you put in the distal taper at the tip and are grinding past where the spine is. For thin flexible blades, I found the aluminum channel piece worked much better.