"Wavy" blade

[lyuv]

Hi all,

I"m forging my first blade. It's suppose to be a 15cm kitchen knife. Somewhat like a gyuto, The main feature is keeping the body of the blade in it's raw forged state - hammered black. The first picture shows the blade after heat treatment (I know, I don't like that blue-ish shade), The second is the current state, half way grinding.

My problem: the grinding revealed that the blade is not perfectly flat but a little wavy. The shiny areas (circled) are raised.

During forging, the hammering had bent the piece all around, and I straightened it by eye. It LOOKED straight, but by eye I can't be all that accurate.

If I had ground the surface (instead of leaving it "raw"), those waves would be flattened.

How do you do it? do you manage to get a good enough flat blade just by forging?

BTW - I"m not talking about thickness issues. Just flatness/straightness.

[JHCC]

I'm working on a similar blade and am encountering a similar problem. The simple answer is, keep grinding. If there's enough metal left in the blade, just grind down to the finished size and shape that exists within your blank.

For my own knife, after investing a considerable amount of time in trying to flatten it post-hardening, I am about to re-anneal it, file it flat, and harden again. I'm regretting the loss of time (and sandpaper) invested, but without a proper knifemaking grinder, it's really my own best option. Don't be afraid to fall back and retrench, if necessary.

[Buzzkill]

I have a few observations for whatever they are worth.  First is your tempering color.  It looks like you may have drawn the blade back a little softer than is usually preferred for a knife edge.

Next, I'm not sure your blade wasn't/isn't straight.  What it looks like to me is those areas you circled were hammered thinner than the areas around them.  When you grind you have to take more off the thicker areas in order to get down to the thinner areas.  It just takes practice to get reasonably consistent thickness across a blade.  This is especially true when starting out:  Forge thick and grind thin.

Also, the heat treat itself can cause warping.  The thinner the blade the more likely it is to warp during the quench.

[Steve Sells]

you are asking for trouble leaving that forge finish on a kitchen knife, there are so many places for bacteria to hide and grow no food service inspector would allow it in the kitchen,

[ThomasPowers]

Buzzkill since temper colour is entirely dependent on the alloy used and that was not given; how can you tell?

As to the OP's question: *practice*!

[Buzzkill]

11 minutes ago, ThomasPowers said:

Buzzkill since temper colour is entirely dependent on the alloy used and that was not given; how can you tell?

I definitely made some assumptions as to what alloy was probably being used.  There's also a reason I used the word "may."

[C-1ToolSteel]

Looks to me like maybe you should have done more bevelling before heat treat. I would anneal it, then straighten it cold in you vise using a three pin setup. After that, you can take a file and finish the bevel with it. Trying to fix a mistake with power tools (especially if you are realitively inexperienced) will often just make a bigger one.

This is looking at it by a knife maker's viewpoint, and not a chef's. If you will be using it past the bevel a lot, that would be something to consider.

[ThomasPowers]

Yes a preliminary grind before heat treat as part of straightening can be a big help.  Also when not having a lot of practice under your belt; leaving the blade thicker to allow for more tweaking with grinding can help too.  The Neo-Tribal goal was to have less than 10% stock removal on a blade and as they were doing it by hand with draw filing it's an understandable *goal*.

Buzzkill, no biggie; just trying to get new people to understand there is no one *right* colour to temper too. (as so many new people seem to think there must be a "best" on anything blacksmith's do...And it's a good idea to provide too much data on what you have done when you have a question than too little!)

[lyuv]

Hi guys,

GOOD points and pointers. Thanks.

First and foremost is not to be the stuborn mule I was (am?), and have the wits and guts to start over. Eventualy I did get a flat grind, but at a cost to a lot of steel, the geometry, and hours of work. Pictures in a few days, when all will be done.

As for the heat treatment - My steel is the common O1, so I suspect that dark shade (rather than "straw") is not so great. BUT, as jokes go, I received bad news and good news: - dropped the blade and a piece of the edge chipped. So your knife is hard, but broken.

As I heated the blade for quenching, it warped like a banana. just from heating. I straightened it, but I suspect there was plenty of stress that manifested during tempering. Is that possible/known?

BTW - I"m not realy worried about bacterias. It's a kitchen knife, but I made it for fun. Don't know if I"ll use it at all, especialy, it being non stainless. In any case, I wire brushed the surface smooth. It still looks forged, but can be cleaned easily.