Straightening via peening

[REK Knives]

I ordered a carbide tipped hammer from JT a month or two ago and just got to use it. I peened the side of the blade until it was quite straight. Then I surface ground off the dimples and the warp comes right back... Just curious how come many recommend it if it doesn't fix the warping? Am I doing something wrong?

 

[Hubert S.]

I have the same issue when grinding bevels. Most of the time, the warp straightens out when I grind the other side of the bevel to match. In AEB-L, this has happened to me both with blades that I had to peen and blades that were straight after heat treating. I really struggle with 0.06" thick material, even going up to 0.08" makes a huge difference for me in terms of keeping the blade straight.

One other thing that seems to help with peening is to use lots of light taps versus a few hard ones. Initially, I made some pretty deep dimples and seemed to have more issues with warps coming back during grinding.

 

[FredyCro]

Unfortunately it's not a magic wand and it has a learning curve, sometimes you need to overpeen to get it straight when you grind the dimples out. A good tip from HSC was to start peening when your grind is getting towards the end. I peen constantly between the grinding now when I do large kitchen knives as some will keep moving all through the grinding. Later it's easy to overdo it and even get s type curves in. After a couple I started to get the hang of it and the blades were straight when finished (with dimples ground out). Just my 2 c.

 

[Natlek]

I ordered a carbide tipped hammer from JT a month or two ago and just got to use it. I peened the side of the blade until it was quite straight. Then I surface ground off the dimples and the warp comes right back... Just curious how come many recommend it if it doesn't fix the warping? Am I doing something wrong?

Obviously forces that keep blade bend are deeper into the steel structure. When you peened that side of the blade you remove some of that forces and that call it new forces holding the blade straight disappear when you surface grind that side .I never liked that kind of straightening blade , i think it hold blade in some kind of constant and unnatural tension ? Maybe one cycle of tempering after blade is peened would help ?
PS. sorry for the dictionary, I know exactly what's going when we peen blade but I can't find the right words for it at the moment. I think it's clear what I mean?

 

[HSC ///]

I ordered a carbide tipped hammer from JT a month or two ago and just got to use it. I peened the side of the blade until it was quite straight. Then I surface ground off the dimples and the warp comes right back... Just curious how come many recommend it if it doesn't fix the warping? Am I doing something wrong?

What steel and what thickness?

Surface grinding can easily induce a bend on one side. Depends on the wheel media used and and how much heat is generated

 

[Justin W]

Grinding can both removed material under stress and induce new stresses. Both can result in a warp. Sometimes, alternating sides can bring a warp back. Sometimes it takes a peen or a bend. Sometimes, you have to cut out the warp.

 

[DevinT]

Try dulling your hammer a wee bit.

Hoss

 

[REK Knives]

What steel and what thickness?

Surface grinding can easily induce a bend on one side. Depends on the wheel media used and and how much heat is generated

It was magnacut @ about 1/8" thick. I surface ground on my SGA with a fresh 984f belt (120 grit).

When I use my real surface grinder I am familiar with warping and can negate it. I think with this maybe I removed too much material but it was only about .010 total between both sides.

 

[Scaniaman]

We should all just stop this and go out and buy some straight knives. Seriously, this goes through my mind regularly.

I use 14c28n, AEB-L'S warpy younger sister. The following helps me: many lighter taps with a not so sharp tip, tapping some during and also after grinding, waiting to grind the blade at least over night since straightening (because straightening/over straightening can happen/finish a fair bit after the hammer hit the steel don't ask me why)

 

[Ken H>]

The thing that helps me with warps more than anything while grinding is to only make one, or at most 2 passes on a side before flipping to other side. A bit of a hassle on the SGA, but it seems to work.

 

[REK Knives]

The thing that helps me with warps more than anything while grinding is to only make one, or at most 2 passes on a side before flipping to other side. A bit of a hassle on the SGA, but it seems to work.

Yeah, that could work but I'm starting off with a warp... So far I'm not impressed with peening. The old way I do it is shim and surface grind.

That could work flipping it though in certain situations, I've got an on/off chuck coming from NRT that I'll mount to my reeder SGA in a few days. That will make it a TON easier

 

[Natlek]

We should all just stop this and go out and buy some straight knives. Seriously, this goes through my mind regularly.

I use 14c28n, AEB-L'S warpy younger sister. The following helps me: many lighter taps with a not so sharp tip, tapping some during and also after grinding, waiting to grind the blade at least over night since straightening (because straightening/over straightening can happen/finish a fair bit after the hammer hit the steel don't ask me why)

I think all that trouble with those steels don t pays off .Cheap steel becomes expensive if you waste three times more time with it than with some more expensive and at the same time much better steel ?

 

[Scaniaman]

I think all that trouble with those steels don t pays off .Cheap steel becomes expensive if you waste three times more time with it than with some more expensive and at the same time much better steel ?

You have a point. Even with the more expensive and maybe better steel in my shop (RWL-34) I have to do quite a bit of straightening though, cryo warps that steel too.
I am only doing this for a hobby, so time isn't as "valuable " for me as forsome others.
Straightening is mostly a time consuming problem with long chef knives though. And 14c28n is just an excellent excellent steel. I am amazed at how well it performs at 61 Hrc.

We should ask PEU about this, he has a significant production volume and still uses a lot of 14c28n.

 

[Hubert S.]

I think all that trouble with those steels don t pays off .Cheap steel becomes expensive if you waste three times more time with it than with some more expensive and at the same time much better steel ?

Josh was using magnacut, not exactly cheap steel.

Which stainless steel would you recommend that does not have warping issues for thin (<0.08") long (>7") kitchen knives?

 

[Natlek]

You have a point. Even with the more expensive and maybe better steel in my shop (RWL-34) I have to do quite a bit of straightening though, cryo warps that steel too.
I am only doing this for a hobby, so time isn't as "valuable " for me as forsome others.
Straightening is mostly a time consuming problem with long chef knives though. And 14c28n is just an excellent excellent steel. I am amazed at how well it performs at 61 Hrc.

We should ask PEU about this, he has a significant production volume and still uses a lot of 14c28n.

Every steel can warp in HT process .Where it will warp depend on shape .To avoid that this is what i do and will do in future .................
I heat treat steel like this / black rectangle/ on drawing , then I found my knife inside that piece of hardened/tempered steel .

 

[Natlek]

Josh was using magnacut, not exactly cheap steel.

Which stainless steel would you recommend that does not have warping issues for thin (<0.08") long (>7") kitchen knives?

I know that he uses magnacut , I was thinking on these two / 14c28n, AEB-L / notorious drunks, known for warping even when they shouldn't We have zillion threads here about Aeb-L warping issue while very little about other steels , it must mean something?

 

[Joshua Fisher]

Did you surface grind both sides? Lots of steels warp while grinding, when I grind the dimples out I make passes on both sides evenly and it stays straight

 

[Hubert S.]

I know that he uses magnacut , I was thinking on these two / 14c28n, AEB-L / notorious drunks, known for warping even when they shouldn't We have zillion threads here about Aeb-L warping issue while very little about other steels , it must mean something?

It could mean a lot of things, e.g., that 14c28n and AEB-L are more popular and that's why you see more posts about them...

I would still like to know what the "more expensive and at the same time much better" steel is that you had in mind when you posted that working with "cheap steel" does not pay off.

 

[Michael Black]

Yeah, that could work but I'm starting off with a warp... So far I'm not impressed with peening. The old way I do it is shim and surface grind.

That could work flipping it though in certain situations, I've got an on/off chuck coming from NRT that I'll mount to my reeder SGA in a few days. That will make it a TON easier

Did you reach out to them directly about buying that? I remember somebody else on here mentioning getting one from NRT and I didn't see it on their site. I'm definitely interested in one for my Brodbeck SGA. It's really the one thing that really bums me out about switching to a SGA from a dedicated surface grinder.

 

[HSC ///]

I ordered a carbide tipped hammer from JT a month or two ago and just got to use it. I peened the side of the blade until it was quite straight. Then I surface ground off the dimples and the warp comes right back... Just curious how come many recommend it if it doesn't fix the warping? Am I doing something wrong?

You are saying that peening doesn’t fix the warping.... but at the same time you say that you peened the side of the blade until it was quite straight.

So it does work and you are likely inducing a bend during surface grinding

I think the peening works great and it’s highly reliable and predictable and it’s been a huge benefit for me

Recently I just heat treated two thin Magna Cut kitchen knives and they came out with huge banana bends that wouldn’t straighten with shimming during tempering but straighten out just fine with peening