Warping while grinding

[weo]

Hello all. I just finished rough grinding (36 grit) a kitchen knife and noticed something strange (but after doing a search, found out it's not so strange). I ground one side completely, it warped, then ground the other side and it straightened. The knife was straight after the tempering.
Now after the search, (and what I was thinking because it makes sense) was that I should go back and forth between sides to prevent this.
My question is, did I do damage to the knife by boing this? It's about 300 layers of 1095/15N20.

Thanks
~billyO

PS- I dunk/cool after every pass, so the blade never got hot

 

[Geoff Flato]

aeb-L is particularly bad about that. This isn't to say there isn't any possibility of an issue, but I have yet to notice an issue as long as the blade ends up straight

 

[kuraki]

Going back and forth doesn't necessarily prevent it, but effectively does. The blade may have stress in it, which you relieve by grinding causing it to have uneven stress left in the unground side. Grinding each side equally keeps the opposing stress equal, keeping it straight.

Building up heat can also affect the stress. Relieving it equally will keep things more consistent.

 

[daizee]

I've had this happen on thin pieces, mostly recently 1/16" AEB-L.

 

[weo]

Thanks for the replies.
So I'm to understand that there was no real damage to the blade (edge) ad that I can safely sell this and not worry about getting a bad reputation if I want?
Or should this end up in my collection?

 

[JTknives]

Warping is a coming problem when grinding things especially damascus steel and is exacerbated when the blade is thin like you have. As long as it was heat treated correctly and you do everything correctly then the knife is fine. How many knives have you made, this is quite a common issue to come across while knife making. There is more to a reputation then questioning a warped blade. Heat treat, grind, blade finish, fit and finish blade to handle, blade shape, handle shape, sharpness, plunge cut center, exc exc. there are so many things that affect the outcome of a blade that we can not say it's good or bad. That is your call and somthing you learn with experance.

Thanks for the replies.
So I'm to understand that there was no real damage to the blade (edge) ad that I can safely sell this and not worry about getting a bad reputation if I want?
Or should this end up in my collection?

Selling the blade is somthing we can not discuss as you have to be a paid member to talk about sales and selling.

 

[weo]

How many knives have you made

If that was a question, this is about my 25th pattern welded one...but I recognize that I'm still very much a novice...

Selling the blade is somthing we can not discuss as you have to be a paid member to talk about sales and selling.

I realize that, I wasn't trying to do commerce here, merely asking for opinions.
Stacy - was this inappropriate?
Thanks
~billyO

 

[Mitchell Knives]

I had this problem when I was grinding a lot of .07" 15N20.

I eventually made a .25" thick template of the knife, and clamped it to the actual blade I was grinding.

This kept the blade from bending, and also showed how much warp (if any) was being introduced.

Grinding the blades wet eliminated the problem completely.

YMMV.

 

[javand]

I haven't had this be an issue on thin damascus or carbon steel, but yes, AEB-L is horrible about it, and i haven't figured out anyway to relieve the internal stresses to avoid this.

One thing you can do in the future to help with other steels though; make sure to normalize properly, and thermal cycle, after thermal cycling, do any rough grinding/surface grinding, whatever heavy machining you're going to do, then, before hardening, do a stress relieving cycle. This'll help not only avoid warp from quench, but also, warping later on, in my experience.

Of course, any heavy hogging at course grit, or taking too large a feed or cut machining after hardening, will put enough stress in no matter what you do to cause you warp again. If that happens, the best/only thing you can do, is to temper it again, which will help.

In industry, it's very common for parts to be given a "stress relieving temper" after any final machining is done, and even after a certain number of "cycles" of use for an object. Usually at 25 degrees lower than the final temper for desired hardness.

They get exponentially longer life from large industrial "knives", by tempering again after using the tool X number of times. There are lots of studies and papers you can read up on it if interested.

 

[stezann]

Peening one side of a blade, or bead blasting, causes the blade to warp and get concave on the opposite side.
It comes also handy so it is a common pratice to straighten a bent blade and it does work well even in the hardened state. Grinding/machining is not so different, if you picture a stream of grit hitting your blade at high velocity.
With this in mind, a lot of strange phenomena get explained, and in the end we try to get even stresses on both sides to have simmetry.