Interesting low spot - need help

[jacobwilder5]

Hi KKF,

I decided to thin and polish my birgersson gyuto and ran into an interesting low spot that I'm a bit at a loss for how to address. I thought I'd ask those with more experience how they might approach this one.

I started with a shapton glass 500 and quickly noticed this spot on the right side of the blade. I moved down to a 220 to see if I could make more progress, but it didn't make a dent. It's near the heel and goes across the entire bevel and is about 17mm long. It's also somewhat circular in shape. I've never seen anything like it, and it seems to be pretty pronounced.

Has anyone seen anything like this? Any advice on how I might approach working through this area without overgrinding would be appreciated.

Here it is in all it's glory:

Thanks!

 

[ethompson]

Can you get a straight edge on it to show me the depth? How’s the other side in the same spot?

 

[refcast]

Yeah take a picture of it with a straightedge in it like a ruler or card. Or take a picture of the knife at an angle almost like a choil shot, showing the grind of the whole knife.

Yeah sometimes there's a high spot on the other side

Have I got super low spots like that before? Yes

 

[ethompson]

Have I got super low spots like that before? Yes

Have I gotten one on a Birgersson? Yes.

 

[jacobwilder5]

Yeah looks like a high spot on the other side.

Did my best on a flat edge to show the low spot I needed to go and make dinner can get a better shot later. There actually look like a slight bend on the last 20mm at the heel along with the low and high spots.

 

[ethompson]

Looks like a bend to me. Not uncommon, not something I'd consider a manufacture defect. With thin forged san mai this happens.

Personally, I think you should tap this out. Look up ura-dashi as it relates to kanna. @refcast probably has more experience than anyone on this forum in performing this on knives. You definitely want to perform some correction prior to continuing rough grinding rather than try and work that out on stones.

 

[refcast]

Yeah check for edge and spine straightness. If its warped just there, then I personally would hammer the iron on the high side, which moves the iron and steel over to the low side to help fill it in.

 

[jacobwilder5]

I’ll start looking into it. I had a feeling it would be a bit more involved to do this right.

Is there a short list of tools you’d recommend to get started?

 

[refcast]

Since you're doing a clad knife, you only need a regular steel hammer. I'd prefer a cross peen hammer for this. The head that looks like a -- . There's peen hammers that are spherical but I feel I have less control.

You don't necessarily need a steel anvil, wood or a textbook or whatnot will work fine for this work. Harder moves the steel more, but higher risk of breakage for higher force, more bends, harder steel.

As long as you start seeing peen marks, the steel and iron are starting to move. Check often by feel, eye, and occasionally by stone.

What I personally use:

Dogyu brand anvil
https://hidatool.com/item/2509

Picard swedish hammer
https://blacksmithsource.com/collec...-forging-hammer-3-3-lbs-1500-grams-cross-peen
1kg one i use

Carbide hammer by Miki giken for hard monosteel
http://www.miki-giken.co.jp/

Go slow because one bad hammer hit and you hit the edge and chip it

The anvils tend to move a bit, so something to keep it in place helps, or a heavier anvil etc.

Displacement of iron and steel via hammer marks. The curved surface area of the peen mark-- into it is where the iron and steel move.

BUT! Please check for edge straightness first. And twists too. If there are twists then a chisel hammer helps more -- the chisel shape provides more bending force like bending a sheet of paper.

For the peen hammer I like to use the end of it, and I hold it at an angle. That's my preferred shape, but you can go to a hardware store and try different shapes.

https://www.kitchenknifeforums.com/threads/japanese-web-info-list.55062/page-2#post-976168

 

[Uncle Danny]

Personally, I would go over it a couple of times more, as it seems that you still have some low spots next to that big spot, get that last sorted out.

Then you could try reaching the last big spot with a bit more angled approach on your stones. Try using them as fingers stones. It’s not an easy task and I wouldn’t blame you for sitting this one out, but hey, polishing is a fun sport with some heavy obstacles once in a while. All part of the game

Second advice in life:
If nothing works, just sand it over