Surface grinding blades, stock straight

JG Custom Metal Works

JG Custom Metal Works

Joined
Nov 27, 2013
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Does anyone here surface grind their blades straight?

I have a wuertz surface grinder attachment for my KMG and, while it works great, the magnet is super strong. When I put a bent blade on it, especially with thinner stock, it flattens it out the bend. Of course I can’t grind the high spots if they’re pulled down flat to the magnetic table.

Does anyone have any idea on how to remedy this problem? Would it work to put a piece of printer paper or two in between the blade and the table?

Would a traditional stone surface grinder work better for this application? I have a couple of those I need to get running. I plan to soon and then could use them.

ETA:

I tried putting printer paper in between the blade and the table and it still didn’t lessen the strength enough to stop flattening out the blade. I used 6 pieces and still no dice
 
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Sure it will, but you have to shim it. Tough to do on a permanent magnet. I like to do the concave side of a bow first, and shim either end.
 
I use a hammer and usually an anvil like Don or sometimes a stump or 2x4 with a groove in it, if the warp is nasty. But usually a small peening hammer I made that is a copy of Eduardo Barros' and the anvil.

I tried the surface grinder once with AEB-L and it kept warping the other way. I don't have coolant on mine but someone on here said they had the same problem while using coolant, might have been Salem. In the end I don't like that a SG removes material as that is not always an option and by the time I dressed the stone I could have had the blade straight just walking over to the anvil and beating on it a little.

-Clint
 
What? You shim to support the piece and grind one side flat. It's now flat in the unconstrained state, so you flip it over and grind the other side flat with no shims. Even thickness and parallel the whole way.
 
kuraki said:
What? You shim to support the piece and grind one side flat. It's now flat in the unconstrained state, so you flip it over and grind the other side flat with no shims. Even thickness and parallel the whole way.
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but alot of new stresses are now made. if the stock is so thin that the mag chuck takes the warp out of it you might get away with an exta temper with the blade tensioned to slightly more then the warp in the proper direction
 
kuraki said:
What? You shim to support the piece and grind one side flat. It's now flat in the unconstrained state, so you flip it over and grind the other side flat with no shims. Even thickness and parallel the whole way.
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And and up with half less thick blade than the original :) Of course depend how bad is warp .Simple way is to straighten blade in tempering process .....at least to do 90% and then light pass on surface grinder ..........
 
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butcher_block said:
but alot of new stresses are now made. if the stock is so thin that the mag chuck takes the warp out of it you might get away with an exta temper with the blade tensioned to slightly more then the warp in the proper direction
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I tried that on 5mm thick blade , and don t work ............
 
Natlek said:
I tried that on 5mm thick blade , and don t work ............
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so your telling me the magchuck pulled the 5mm blade flat? i have not worked with many mag chucks but ether way if it pulls the warp out of the part you are just grinding new stresses into it and it will likly be just as bad if not worse when taken off the chuck
 
butcher_block said:
but alot of new stresses are now made. if the stock is so thin that the mag chuck takes the warp out of it you might get away with an exta temper with the blade tensioned to slightly more then the warp in the proper direction
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Grinding doesn't create stress. It relieves it. It may relieve it in a way that creates new warping. Cold forming does create stress.

Natlek said:
And and up with half less thick blade than the original :) Of course depend how bad is warp .Simple way is to straighten blade in tempering process .....at least to do 90% and then light pass on surface grinder ..........
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I'm not suggesting you grind a 2.5mm bow out of a 5mm thick blade. That's nonsensical. So is the idea that you can get something truly flat and parallel with a hammer or a counter-bow in the temper. I'm only pointing out how you can get something with minor warp truly flat and parallel on a surface grinder, perhaps after taking the majority of warp out with your hammer or temper.

Not every discussion of methods is a simple dichotomy.
 
Question please; when you use the hammer method, is it pre heat/temper or post heat/temper?
 
The steel is going to have stress and counter stresses across the cross section when you receive it. And because the yield point is different under tension than compression you'll get a combination of different stress across the thickness that are relieved as you cut into it.

One way to visualize this is imagine bending a piece of metal. The outer surface yields in tension and the inner surface yields in compression. Then you bend it in the other direction but to a lesser amount and only the very surface skin yields. You might end up with a straight piece of metal because the forces are canceling each other out but once you remove the skin the stressed material under that skin will make the metal distort again. Attempting to get your piece super straight too soon might be a fools errand because unless it's been annealed again it will frequently just move again.

And cutting and grinding create additional stresses.

To my knowledge the only way to straighten something and not have gradients is to stretch it. Most people don't fool with this.

Most batches of steel have a pretty consistent yield point from piece to piece so a certain amount of deflection across a certain distance will end up with the piece reasonably straight in a predictable way once the force is removed. We do this in a little press and use shims to control that dimension. S bends require a little extra attention.

At the end of the day a lot of it becomes moot during heat treat. And that introduces distortion too, which is easy to remove after heat treat during temper with little shims. Nothing is ever flat but we measure and have a tolerance. Half a thou per inch is pretty good meaning you can get a .005" feeling gauge under a 10" piece on a surface plate. Much more than that becomes noticeable.

Just my .02
 
Thanks for the info gents, I really appreciate it. I was hoping for a quick, easy fix for my problem. A way to chuck a piece into a machine, turn it on, and pop it out straight. Wishful thinking as usual on my part.

Thus far it seems as though I’m horrible at straightening blades. A lot of the time, when I try it by hand, I end up making it worse. I’ve tried straightening during the annealing process and it’s probably worked the most consistently for me. But it doesn’t really work for real crooked blades.

Would it work to try and straighten a blade in the oven, at tempering temps, prior to hardening? Also, when is the best time to normalize? If normalizing relieves stresses in the metal, would that have a straightening effect on it? Or would it just remove the stress and leave it in the bent state? I’m thinking that the best thing to do would be to grind, straighten, normalize, harden, and finish.

Where does annealing fall into the mix? Most steals come pre-annealed. In terms of keeping things straight along the entire process, would it be good to anneal in the beginning? Between the annealing, normalizing, hardening, and tempering, you’d really be racking up the hours for electricity usuage. I’m thinking that annealing might be the one to trim as long as the steel is already annealed from the distributor.

Lastly, as far as high carbon steals are concerned, is there a general annealing process? Or is it specific to each blade type? For instance, I have a fighter in 1084 that’s bent and a bowie in W2 that is too. Would I be able to throw them in my Evenheat at the same time, using one firing schedule?

Thanks again for the responses everyone. I appreciate it
 
Yes, cutting and grinding do create new stresses, it's always best to do a final temper after any of this kind of work, even finish grinding. Most of us don't, but IMO it's optimal if you do. In industry they'll often re-temper tooling after a certain number of cycles, and there's all sorts of papers out there detailing the advantages of a "stress relieving temper". If you take light passes with a surface grinder (I only take max a thou DOC when grinding hardened steel, and usually half or quarter thou for the final passes for really nice finish with a finely dressed stone), you won't introduce any more stress than you do finish grinding bevels or similar.



Yes, you can also remove a warp with a surface grinder, it's one technique of many, Kuraki above mentioned that shimming is necessary. I do this ALL the time to remove minor warp, that's quicker than doing a straightening temper or other method on hardened blanks. For small slipjoints, I usually don't forge them, or rough grind prior to HT, and one out of a half dozen will often have a tiny amount of warp, usually consistent across the length.

There's two quick ways to fix this;

1) take the side where the inside of the bow is (both ends land when laid across a surface plate, but the center isn't touching), and quickly grind this flat, holding both ends, without applying center pressure, across the top of a disc grinder with course paper (80-120). All you want is rough and reasonably consistent. Yes, in theory this puts you out of your original parallel but if done correctly is inconsequential, even to your pivot pin orientation. If done incorrectly though, you'll grind way more off one side or the top/bottom and throw shit out of whack.

Then, debur the edge, and then check to make sure the blade lays flat across a surface plate, making contact across the length of the blade. If so, take this side, and place it *down* on the surface grinder magnet, since this is a hardened blade, take gentle light passes cutting the outside bowed side, if you did the previous step right, it'll start cutting the center of the blade first. If you take 0.0005 DOC even with tiny thin slipjoint blades you won't introduce any new warp or cause any overheating. If the warp was minor, you should only need a few thou, then flip, and repeat. After this, you'll have a straight, parallel blade, and you'll have it finish surface ground, if you're doing a slipjoint, obviously you want to do this process with the blade's matching spring.

At this point you've got a tang and spring ground together, and everything should be straight and parallel.


2) The second option, is to take the blade, and lay it on the magnet, and shim the center or the ends, with post it-notes, usually it's no more than one or two, if it is, you've got enough warp that it's likely more efficient to straighten by other methods, shim the center or ends (center is best), being sure to not to over shim, actuate the magnet, observing to make sure the piece doesn't move from magnetizing (if it does, adjust shims), cut that side until it's cutting across the entire blade, using light passes again, flip, repeat.



Something many people also don't seem to realize, if you ever surface grind a forged blade or rough ground blade's ricasso, that has any taper in it, if you don't shim all the points that aren't contacting the magnet with your finger pressed on the ricasso, you're not grinding either side (above or below) of the ricasso parallel, the areas that get pulled down to the magnet, will get ground, but the ricasso will be concave to them, once it's demagnetized, and after you grind one side, you'll compound inaccuracy when you grind the other side. Many likely won't understand why everything looks warped after that, but it's not that you introduced warp by stress, it's because you were essentially warping the piece, and grinding bows into it.
 
JG Custom Metal Works said:
Thanks for the info gents, I really appreciate it. I was hoping for a quick, easy fix for my problem. A way to chuck a piece into a machine, turn it on, and pop it out straight. Wishful thinking as usual on my part.

Thus far it seems as though I’m horrible at straightening blades. A lot of the time, when I try it by hand, I end up making it worse. I’ve tried straightening during the annealing process and it’s probably worked the most consistently for me. But it doesn’t really work for real crooked blades.

Would it work to try and straighten a blade in the oven, at tempering temps, prior to hardening? Also, when is the best time to normalize? If normalizing relieves stresses in the metal, would that have a straightening effect on it? Or would it just remove the stress and leave it in the bent state? I’m thinking that the best thing to do would be to grind, straighten, normalize, harden, and finish.

Where does annealing fall into the mix? Most steals come pre-annealed. In terms of keeping things straight along the entire process, would it be good to anneal in the beginning? Between the annealing, normalizing, hardening, and tempering, you’d really be racking up the hours for electricity usuage. I’m thinking that annealing might be the one to trim as long as the steel is already annealed from the distributor.

Lastly, as far as high carbon steals are concerned, is there a general annealing process? Or is it specific to each blade type? For instance, I have a fighter in 1084 that’s bent and a bowie in W2 that is too. Would I be able to throw them in my Evenheat at the same time, using one firing schedule?

Thanks again for the responses everyone. I appreciate it
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You ask to many question at once :) I have little knowledge about this but this is the way I do .... I use anealed steel ready for HT and I straighten piece of steel with hammer before I cut blank in shape .Then I grind bevel and I learn fast that even/simetrical grind is crucial to get straight blade when quench. When I put blade in HT oven I wait till it get dark red color and I pull out blade and wait little and then check is it straight .Then I HT and I pray that will come out right ;)
 
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JG Custom Metal Works said:
Thanks for the info gents, I really appreciate it. I was hoping for a quick, easy fix for my problem. A way to chuck a piece into a machine, turn it on, and pop it out straight. Wishful thinking as usual on my part.

Thus far it seems as though I’m horrible at straightening blades. A lot of the time, when I try it by hand, I end up making it worse. I’ve tried straightening during the annealing process and it’s probably worked the most consistently for me. But it doesn’t really work for real crooked blades.

Would it work to try and straighten a blade in the oven, at tempering temps, prior to hardening? Also, when is the best time to normalize? If normalizing relieves stresses in the metal, would that have a straightening effect on it? Or would it just remove the stress and leave it in the bent state? I’m thinking that the best thing to do would be to grind, straighten, normalize, harden, and finish.

Where does annealing fall into the mix? Most steals come pre-annealed. In terms of keeping things straight along the entire process, would it be good to anneal in the beginning? Between the annealing, normalizing, hardening, and tempering, you’d really be racking up the hours for electricity usuage. I’m thinking that annealing might be the one to trim as long as the steel is already annealed from the distributor.

Lastly, as far as high carbon steals are concerned, is there a general annealing process? Or is it specific to each blade type? For instance, I have a fighter in 1084 that’s bent and a bowie in W2 that is too. Would I be able to throw them in my Evenheat at the same time, using one firing schedule?

Thanks again for the responses everyone. I appreciate it
Click to expand...

Just wanted to ad, as I've told some people before, I was at one point so frustrated with straightening, that I almost quit making knives. Learn as many techniques as you can, and eventually you won't even think about it.


Straightening in the temper usually works the best for me. To the point that I always do my first temper, 25-50 degrees lower than my final temper, because I know I want the option to straighten in my second temper, which in my experience, is more effective if you do the straightening after the first temper, but hotter than it.

I use a piece of angle iron that's 3/16" thick, I use 2 or 3 scrap steel "shims" that are the same thickness, maybe half an inch wide and an inch or so long, but sometimes I'll find bigger or smaller ones to help a tricky warp. If it's a good even bow, find a couple of flats on either end of it, place the shims, and use a small "Kant Twist" clamp (these will survive repeated oven use, as they're designed to be exposed to heat), and then adjust the piece until you're straight, and then go just a tiny bit farther, essentially making it warp in the opposite way, just a pinch, if you over do it, you'll just warp it the other way. Make sure and fiddle with the clamp a bit, these things have an optimal orientation, and if they're not in that place, once it moves it'll release pressure, make sure it's tight at the spot you want it, then put this whole assembly in your tempering oven, at 25-50 degrees or so (or whatever, the trick is to be hotter than your first temper), and temper for another hour. Then (and in my experience this is critical), let it oven cool, without opening it, once you remove it, the warp will be gone.

More stubborn warps can be done by doing the above, but after letting it equalize at temp, you remove the whole thing, and quickly quench in water, in my experience though, usually you don't want to clamp past the warp if you quench it, as it'll set very precisely where it's clamped in this case.


I've never done the quench method with high tempering temp stainlesses, just carbon steel, so I'd be wary of that, and do another final temper afterwards.

I've removed some really crazy compound warps with this method though, even warped edges of thinly rough ground blades, that warped during hardening.
 
Am I misreading here? I kind of assumed he's asking about straightening hardened blades/blanks?

Edit: Missed the OPs reply. Yeah, if they're annealed/not-hardened, you really need to just straighten them by hand.

Smack em with a hammer, stress relieve before hardening after all previous work is done.
 
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