How Do I Get Chef Knives Dead Nuts Flat?

S

SteveGallo

Joined
Apr 29, 2014
Messages
45
Most of the knives I've made so far have been 8.5" chefs from 3/32 15n20. The largest issue I am having is making them absolutely FLAT. The steel comes from Aldo and is great, but at that thinness it doesn't even come out of the tube perfectly flat. I don't own a flatter, and even if I did, my anvil isn't big enough to use one anyway. - is there any other reliable method for getting these thin chef knives perfectly dead nuts flat? I rough grind, then draw file to remove waves, but not having an absolutely flat blade is driving me nuts!

Thanks for the help!
 
It's a bit of elbow grease but what about gluing sandpaper to a surface plate and sanding it on there?
 
Fletch Helical said:
It's a bit of elbow grease but what about gluing sandpaper to a surface plate and sanding it on there?
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I should have been more specific with my question; I'm not looking to remove waves from a blade (of course that's always a concern), but rather to make sure there's zero curvature in the stock to begin with. The flattest thing I own is my glass top stove, and if I lay the work on it, it has minor yet glaring bending/warping. I'm basically at a point where I've cut the shape of the blade outt with an angle grinder but haven't done any grinding yet, and I want to know how I can flatten the thing out

Edit: Here's a pic of what's going on. All of my knives start of having this issue to some extent, as all the stock I've ordered this thin never comes straight.

vo5yjt.jpg
 
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Try doing what most people do when their quenched blades curve or warp.. Put it in an oven at about 400F (or higher since it's not heat treated yet) and use a piece of angle iron with some metal shims and use c-clamps to over-correct the curve(s) a bit and let is temp for an hour, then take it out and quench it in water if it's straight (enough). Then you can flat sand it.

Or if you have a forge or a HT oven heat it up to a bit over critical temp or around a forging temp and try clamping it heavily between tw steel plates, then of course normalize and anneal afterwards then grind. Or use a flat wooden stump and light hammer blows at a forging temp to hit it straight. Check out some techniques Murray carter does when he forges his kitchen knives... He straightens each one a number of times throughout the process of making one. I'm sure there are a number of ways you can think of to straighten it while it's hot... Use a vice and clamp it at a forging heat and play around with shims there as well if needed.

Watch these vids and check out how he straightens..

[video=youtube;UqwxkyaSws8]https://www.youtube.com/watch?v=UqwxkyaSws8&list=PLRXwH4gb88trIMqQUiKSOsDPSMFEMAGs6&index=22[/video]

[video=youtube;HrasEQhVOLo]https://www.youtube.com/watch?v=HrasEQhVOLo&list=PLRXwH4gb88trIMqQUiKSOsDPSMFEMAGs6&index=48[/video]

Hope this helps you come up with some ideas :)

~Paul
My YT Channel Lsubslimed
 
I heat to about 1400° then clamp between 2 pieces of 2" angle iron. It gets it 95%there. Then normalize as usual.
 
Kieran Klein said:
I heat to about 1400° then clamp between 2 pieces of 2" angle iron. It gets it 95%there. Then normalize as usual.
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My concern with trying something like this is that 15n20 air hardens, so I'm worried I would have to anneal before working it again. I don't have vermiculite or ash on hand, but I suppose that if this is the best way to flatten the blade I will have to get some.

I've seen those Murray Carter videos before, and I was always hesitant to try what he does. Cold forging/cold straightening seems to work for him, but I've also read to never attempt to flatten a blade below 400°, so I'm not sure what to believe there.

I think I will try gently flattening it cold, and if that doesn't work I'll invest in materials to anneal. I'll go to hand sanding/draw filling to get it the rest of the way.

Thanks for all the input.
 
Steve, that knife looks to me like it has one nice, gentle curve from tip to tang. I know what you mean about thin stock. I have some of Aldo's 1095 that looks like the waves of a surfing beech! But that curve looks to me like it can be taken care of easily during tempering. I would say go ahead and heat treat it. Run ONE temper at a low 350F first. Then use the 3 point clamping system for straightening knives. A search here on BF will bring lots of results on how to do that.

I had a chef's knife do exactly that after hardening. The 3 point system worked perfectly. It was dead flat when done. You have to use 400F or higher, but make sure you run one quick cycle at 350F or so first. If you don't, when you put it in your three point jig and crank down, it may snap. One temper will prevent that.
 
It seems like it is not heat treated yet if you are planning to draw file the bevels, so in that case bend it by hand or with a soft material mallet on a stump. It will probably warp in heat treat to some degree so that is when you counter bend with clamps at tempering heat.

Supposedly Peters Heat treat is know for getting blades very straight after HT, I would love to know how they do it if anyone has any idea. Warped long thin blades drive me nuts!
 
SteveGallo said:
My concern with trying something like this is that 15n20 air hardens, so I'm worried I would have to anneal before working it again. I don't have vermiculite or ash on hand, but I suppose that if this is the best way to flatten the blade I will have to get some.

I've seen those Murray Carter videos before, and I was always hesitant to try what he does. Cold forging/cold straightening seems to work for him, but I've also read to never attempt to flatten a blade below 400°, so I'm not sure what to believe there.

I think I will try gently flattening it cold, and if that doesn't work I'll invest in materials to anneal. I'll go to hand sanding/draw filling to get it the rest of the way.

Thanks for all the input.
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Your right I do find that even 1084-80crv2 hardens a bit when doing the angle iron straightening. I just throw it in the oven for 1250 for 45 min or so and that anneals it well for me. I just do it as part of the process
 
If that is the condition in which you received the steel, then it should be in a spherodized condition.
I would go ahead and "three-point" striaghten the blade.
Now, Ray Kirk, MS, sell a ton of 15N20 and makes lots of knives from it.
He plate quenches his 15N20 - you even said it air hardens.
There is no need to oil quench it.
Go ahead and straighten the steel - give it an austenizing soak and plate quench between a couple aluminum blocks. (You can get them on ebay!)
The plate quench may give you what you want.
 
1200 F for two hours is a sub-critical anneal/ stress relief temper .It's good to take out stress from the original material which often has been rolled . Use before HT.
 
Karl B. Andersen said:
If that is the condition in which you received the steel, then it should be in a spherodized condition.
I would go ahead and "three-point" striaghten the blade.
Now, Ray Kirk, MS, sell a ton of 15N20 and makes lots of knives from it.
He plate quenches his 15N20 - you even said it air hardens.
There is no need to oil quench it.
Go ahead and straighten the steel - give it an austenizing soak and plate quench between a couple aluminum blocks. (You can get them on ebay!)
The plate quench may give you what you want.
Click to expand...

I didn't even think of plate quenching, which I have never done. You're saying I don't need an oil quench at all? What I've read about plate quenching, most people seem to do a quick quench followed by a plate quench. Can you elaborate on this?

I would try that Mete, but I don't have the equip to hold at that temp.
 
Murray Carter has less issues straightening and cold forging because his blades are forged with a low carbon body and high carbon edge insert. The cheeks support the thin edge. I think this is a great way to go about it. Alas, my forge-welding sucks so I have to improvise. Keep in mind, I like the Japanese "forge finish" look. For thin kitchen knives I...

Normalize and refine grain after forging
Make sure to leave stock
Minimal grinding to clean up for quench
Stress relieve prior to final heat treat(I heat to red but still magnetic a couple times
Quench in oil, transfer to aluminum plates to play out to Mf
Run a couple temper cycles
Put edge in tray of water and torch the crap out of the spine
Grind and straighten with a brass hammer on a stump.

Ideally, I should just learn proper forge welding technique... for now, I fake it.
 
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Edit- Thought it looked like you had ground your bevel(s), then I re-read your post. That is strange to get that much deformation just from grinding the profile. I would guess it's a function of your tooling (table of the grinder not supporting the blade enough maybe?), hard to say though.

I've had to combat this on all my knives made from AEB-L and the thinner 440c knives, both before and after heat treat. If you are doing a single sided grind, it will be a major issue. Like everyone has said, you just have to straighten as well as you can if that's the case. I just do it by hand. Now, if you are grinding both sides to a center line, with some practice you can get it to come out flat by working back and forth a bit and modulating how you apply pressure during the grind so it's more or less straight at the end. With S30V, it seems to be impervious to bending (under normal conditions), even when annealed. Honestly, I'm done with AEB-L because I got sick of dealing with it, it would develop curves during finish sanding.
 
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I've always straightened bar stock cold with a piece of leather
on the anvil using a hammer. Never a problem in 25 years...
 
Rick Marchand said:
Murray Carter has less issues straightening and cold forging because his blades are forged with a low carbon body and high carbon edge insert. The cheeks support the thin edge. I think this is a great way to go about it. Alas, my forge-welding sucks so I have to improvise.
Click to expand...

Good point Rick, I forgot to take into account the "soft" outer layers of the san mai, which would deffinitely make it easier to straighten without the blade wanting to return like a spring. :thumbup:

Ideally, I should just learn proper forge welding technique... for now, I fake it.
Click to expand...

You're kidding me, even I can forge weld, (maybe not the best at it, but.. ;) ) and you're deffinitely WAY better at forging than I am and have a LOT more experience than I do. I think you would be great at it if you started doing it. So are you saying that you "can't" forge weld, or that you don't feel that you would be putting out optimal perfoming (san mai etc.) blades (to your standards at least) with the techniques you are using at the moment.. Because my guess would be that you are selling yourself short and/or being too picky about your technique but you are able to do it :D Have you made any san mai or damascus knives in the past? If so, have any links to any pictures? I'm a big fan or your style btw :cool:

Anyway, sorry for getting side tracked here guys! :foot:

~Paul
My YT Channel Lsubslimed
 
Ha! I have made San Mai and pattern welded blades. I just haven't made enough to get good at it and should set aside the time to get it consistant. I want to do it the way Murray does(splitting the steel and inserting the high carbon bit). I like mono-steel for camp blades, choppers and swords but I think the san mai would best suit my idea of a kitchen knife. I like being able to go ridiculously thin and "tune" the blade true.
 
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