Jump to content

Problems making a chef's knife


Recommended Posts

I am trying to make a chef's knife for my wife, and I overheated the blade upon grinding, had to take off some of the belly, then during hand sanding I noticed that I still had a soft spot on the blade.  I re-hardened, but with the de-carb I lost some additional depth and I am ready to scrap the blade.  The questions I have are around grinding technique, I am assuming I am running my grinder a too high of a speed?  Also, should I try and re-profile the blade as something else or take the opportunity to break it and see what the grain structure looks like?  Any tips or guidance on design and aesthetics are welcome as well.  Thanks.  The first picture is the original profile, the second is before I found the soft spot.  I didn't take a picture after I re-hardened, but I lost and additional 3/8".

20210829_163551.jpg

20211110_171205.jpg

20211110_170551.jpg

20211110_171230.jpg

Link to post
Share on other sites

Tips and edges are what usually overheats during grinding. Are you sure the blade was properly hardened to begin with? 

 

Anyways, to prevent overheating when I grind, I use fresh belts and my bare hands. When it becomes too hot to the touch, I dunk in water. Usually 2 passes between dunks at first and one per dunk when the blade gets tinner. I also progressively reduce pressure as I get closer to the tip. 

Link to post
Share on other sites

I do all my material removal to get my edge where I want with 24 grit....then 80 to get rid of the 24 lines...then go to the trizac 300 to get rid of the 80 grit lines.

I guess if the point I am attempting to make is things are going to get alot hotter alot faster the finer grit you use.

I only use them the minimal amount needed.

Link to post
Share on other sites
17 minutes ago, Joël Mercier said:

Tips and edges are what usually overheats during grinding. Are you sure the blade was properly hardened to begin with? 

 

Anyways, to prevent overheating when I grind, I use fresh belts and my bare hands. When it becomes too hot to the touch, I dunk in water. Usually 2 passes between dunks at first and one per dunk when the blade gets tinner. I also progressively reduce pressure as I get closer to the tip. 

I don't know for sure that it was hardened properly, it did pass the file test, but I don't have a method to check the actual hardness.  Thanks for the tips on grinding, I think I may be using too much pressure, and probably too old of belts.  Do you use lower speeds as well when you get to higher grits or keep the same speeds?

11 minutes ago, Kreg Whitehead said:

I do all my material removal to get my edge where I want with 24 grit....then 80 to get rid of the 24 lines...then go to the trizac 300 to get rid of the 80 grit lines.

I guess if the point I am attempting to make is things are going to get alot hotter alot faster the finer grit you use.

I only use them the minimal amount needed.

Thanks, I may be using too many grits.  I do 36 to 80 to 120, etc.  

 

Link to post
Share on other sites
29 minutes ago, Conan Dunlap said:

Do you use lower speeds as well when you get to higher grits or keep the same speeds?

Yes. I go full speed on 60 grit or coarser. 60-70% on 120 grit and so on ...

 

 

Link to post
Share on other sites
32 minutes ago, Conan Dunlap said:

don't know for sure that it was hardened properly

A good trick is to grind off the decarb and dunk the blade in ferric chloride. Any softer spots will show lighter than the rest. 

  • Like 1
Link to post
Share on other sites
On 11/17/2021 at 4:05 PM, Conan Dunlap said:

Thanks, I may be using too many grits.  I do 36 to 80 to 120, etc.

I do things very differently from Kreg, and I have some "rules" (more like guidelines) on grinding.

At any grit level progression, go no further than double the number, or half the grit size. If you start at 60 grit, the next step is no finer than 120, etc.

Rough grind is done before hardening and depending on the forging quality, I tyically start at 60 and finish at 120. Then I got to hardening and tempering. Grits rougher than 60 are only used for really gnarly forgings where I need to remove a lot of material. My edge is usually about  .05" when I go to harden.

Finish grind starts at 120 and goes up from there through these steps: 220-320-400-600-800. Not all knives get past 400 and many of them stop at 400. I use a disc sander for all grit levels 120 and higher with 320 and higher only on the disc. Rarely do I go above 220 on the belt. The exception is the Trizac A45 to set and polish plunge lines when I have them.

 

If all you have is a belt grinder, you can use the higher grits, but the danger is leaving the platen marks in the steel. This is why a lot of us do a hand finish inline with the blade rather than across the blade. I would suggest that on grits above 220, you go from the belt to hand sanding. You could always go from 220 on the belt to 320 by hand and call it good. A 320 hand finish looks fine for most user-knives and it's going to get jacked up the first day it gets used anyway. It takes a little more work to thougoughly jack up a 320 grit finish than it does a 600 grit finish too.

 

Tell us about your hardening/tempering regimen and we can provide better feedback. FWIW, The knife looks pretty good.

Link to post
Share on other sites

Wow, my progression has evolved to be surprisingly similar to Joshua's.  The big difference is I don't have a disk. (yet...)

 

I start at 60 (if necessary) for rough grinding, and finish at 120 for heat treating.  This is all done with ceramic belts.    I've generally gotten away from using anything more aggressive than 60 grit with a blade, but I do use 36 grit belts when I am cleaning up surfaces on billets that I will restack and weld again.

 

After heat treat, I start with a fresh 120 grit ceramic, and run it fairly slow with lots of water.  I like to see the metal shavings falling from belt.  I know ceramics don't like to run slow, but for some reason this works well for me.  After the 120, I move to cheap AO 220 and 320 belts.  At a buck each, I use them like they are free.  Then I start hand sanding at 220 with rhynowet and work up to whatever level of finish I need for that knife.

 

Sometimes I use trizacs in slightly finer grits, but this is usually when I have a hollow ground blade, and want to leave the machine sanding/grinding lines in the blade bevel.

 

 

Edited by Brian Dougherty
Link to post
Share on other sites

I suppose there is more than one way to get there. He was mentioning having trouble with a final sharpened edge.

When I take it with 24 grit and get a burr that looks like this ....I know my finished edge is going to be sharp AF. 

I harden with my edge at least as thick as a dime. I personally cant see any reason not to go at it with the 24 until you get to this point

Takes longer....uses more belts.....more overheating risk using finer belts for longer periods.

I hear of guys hand sanding to 400 grit before quenching....again I just dont see the point.

To each his own I guess.....grind on.

24burr.jpg

Link to post
Share on other sites
26 minutes ago, Kreg Whitehead said:

I suppose there is more than one way to get there.

Yes, there are many ways to get "there", and depending on where "there" is, some ways are easier than others. Grinding, especially the finish grind, largely depends on the type of bevel (flat, convex, hollow, etc.) and the maker's desired finish level. Hollow grinds are typically finished differently than flat grinds. Scotchbrite belt finishes hide a lot more than 600 grit sandpaper. 

 

When it comes to creating the edge, the geometries are more or less the same. How you get there, is less important than getting there.

 

33 minutes ago, Kreg Whitehead said:

I personally cant see any reason not to go at it with the 24 until you get to this point

That really depends on what you want the finished surface to look like. I can think of many reasons to not do that, and instead walk the edge down over successively higher grits until the burr appears. Most of my reasons pertain to the level of finish I want on my blades.

Link to post
Share on other sites
2 hours ago, Joshua States said:

Yes, there are many ways to get "there", and depending on where "there" is, some ways are easier than others. Grinding, especially the finish grind, largely depends on the type of bevel (flat, convex, hollow, etc.) and the maker's desired finish level. Hollow grinds are typically finished differently than flat grinds. Scotchbrite belt finishes hide a lot more than 600 grit sandpaper. 

 

When it comes to creating the edge, the geometries are more or less the same. How you get there, is less important than getting there.

 

That really depends on what you want the finished surface to look like. I can think of many reasons to not do that, and instead walk the edge down over successively higher grits until the burr appears. Most of my reasons pertain to the level of finish I want on my blades.

I agree totally with the how you get there is less important than getting there part.

At the end of the day I could care less what you or anyone thinks of the way I do it....and I equally dont care how you do it.

I am not to smart to learn anything so maybe you can spell it out for me how the way I am doing it isnt going to let me get any level finish I want?

For discussion sake lets say we are talking 120 grit.....the belt that you start your finish grinding with...because if we are equal to that point the rest of it is pretty irrelevant I would think.

I grind with 24....I dont always go all the way to a burl.....if I were making a 1/8 kitchen blade I would probably try and head into that with more like an 80 before the 24 got that far.

After the 24 or 80 I paint a bunch of sharpie on both sides of the blade and go 120 until the sharpie has vanished....now I am at 120.

How exactly is it that your 120 is superior because it took you longer and you used more belt $ than I did?

Legit question.

 

Edited by Kreg Whitehead
  • Like 1
Link to post
Share on other sites

First of all, this is starting to hijack Conan's thread. Secondly, you seem to be taking it personally and it isn't. We are two very different makers with different processes. Nobody said my way was superior to yours and the assumption that my way takes longer and uses more belts is just that, an assumption. You have never seen me grind a blade and I have never see you do so. We only know each others' work from photos we have seen here. Not a really great way to gauge. 

14 minutes ago, Kreg Whitehead said:

For discussion sake lets say we are talking a 120 grit belt that you start your finish grinding with...because if we are equal to that point the rest of it is pretty irrelevant I would think

I wouldn't think that were true at face value, because you haven't said how you get from 120 to whatever level you finish at. If you go from that 120 straight to a 400 grit finish, I would bet serious money it takes you a lot longer to get there than I can get there by stepping through 220 and 320. Especially using the disc sander. I'm not trying to say my way is "better" than your way. This is about options. Your post gave me the impression that you went from 24 to 120. I have tried going from 36 to 120 and it takes me a lot longer than it does to go from 36 to 60 to 120. I can't imagine how long it would take to remove 24 grit scratches with a 120 belt on a flat grind. Maybe on a wheel, and a serrated wheel would be much more aggressive, it would take less time than a platen, but Conan is talking a kitchen knife. I don't think hollow grinding techniques apply.

 

You have your way, I have mine. We disagree. So what? Conan can try both and decide which way he likes best. Let's just leave it at that.

Link to post
Share on other sites

I jump as many grits as possible. I regard each successive grit as only removing the 'ridges' from the previous one, not grinding 'virgin' steel, just knocking the ridges off. I dont see the point in doing this progressively. 

 

I don't get on with 24g belts, but never tried a quality one, on a suitable machine. 36g ceramics sometimes.

 

 I generally go 60 / 120 on the belt grinder. Its only a couple of passes at 120 to move the ridges from the 60 grit. All the work is done with the coarse belt. I then hand sand (or use a wet stone grinding wheel, but that's not relevant to this conversation!)

 

A 120 grit 'hand sand' is a totally different finish to a 120 machine belt finish. The trick  to efficiency for me is getting it 'true' and accurate with the coarse belt, everything else is a finishing operation, 120 machine grit is a couple of passes, and if your accurate, hand sanding takes no time at all. (ie, not chasing a wobble out of it for hours hand sanding)

 

Edited by John N
  • Like 2
Link to post
Share on other sites
17 hours ago, John N said:

The trick  to efficiency for me is getting it 'true' and accurate with the coarse belt,

I true all my knives on the disc. All those "wobbles" from the belt dissapear at 120 or 220. 

 

Link to post
Share on other sites
On 11/17/2021 at 3:39 PM, Joël Mercier said:

A good trick is to grind off the decarb and dunk the blade in ferric chloride. Any softer spots will show lighter than the rest. 

That is a great idea, thanks.  I will have to try that on the next one.  

 

On 11/19/2021 at 12:26 PM, Joshua States said:

Tell us about your hardening/tempering regimen and we can provide better feedback. FWIW, The knife looks pretty good.

Thanks, I love doing this, I hope I can get to the ability level of some of you guys some day!

 

I did 3 normalization cycles at 1600 F, 1550 F, then 1500 F.  This was done wrapped in stainless foil to try and prevent decarb, but I am afraid I am not getting the blade itself up to the correct temperatures because when I take the blade out of the foil, I don't see the colors I would expect.  I quenched at 1500 F the first time with a clay coating to prevent decarb.  The second quench I went up to 1600 F and skipped the clay.  I quenched in Parks AAA oil.  

 

Sorry for the late reply, I was out of town for a while.  Thanks to all for jumping in and giving me advice, I appreciate the help!

Link to post
Share on other sites

I was struggling with putting an edge on a small kitchen knife just yesterday afternoon.

For me the conundrum is getting the things sharp without cooking the edge, versus not hand sanding a sharpened knife........have don't it on occasion, but I try to avoid it as far as possible.

Link to post
Share on other sites

If you've got a variable speed grinder, new belt , slow it way down, just above a crawl,, and very little pressure,  let the belt do the work. On a single speed I use on brand new belt to cut the angles then its to sharpening  stones.

Link to post
Share on other sites
16 hours ago, Conan Dunlap said:

I did 3 normalization cycles at 1600 F, 1550 F, then 1500 F . . .  quenched at 1500 F the first time . . . second quench I went up to 1600 F

 

15 hours ago, Joshua States said:

What steel is this?

 

I'll second this question.    According to my Dr Larrin Thomas's book, there's 1600F is not a recommended quench temp for any of the alloys he writes about. 

The steels that require at least 1500-1525 austentizing temps are: A6, 8CrV2, 52100, 5160. 8670 & L6.    So if it's not one of these, you either quenched a few hundred degrees cold, or a bit too hot which will grow grain unnecessarily.

Link to post
Share on other sites
1 hour ago, billyO said:

So if it's not one of these, you either quenched a few hundred degrees cold, or a bit too hot which will grow grain unnecessarily.

And if it's anything other than O1, AFAIK Parks AAA is a medium speed quenchant, probably not ideal.

Link to post
Share on other sites
18 hours ago, Joshua States said:

What steel is this?

 

Hi Josh. Conan mentioned in WDYDIYST that it is 80CRV2. I’d initially thought he might have ground through a shallow hardening steel.

Link to post
Share on other sites
5 hours ago, billyO said:

 

I'll second this question.    According to my Dr Larrin Thomas's book, there's 1600F is not a recommended quench temp for any of the alloys he writes about. 

The steels that require at least 1500-1525 austentizing temps are: A6, 8CrV2, 52100, 5160. 8670 & L6.    So if it's not one of these, you either quenched a few hundred degrees cold, or a bit too hot which will grow grain unnecessarily.

Yes, I am sure that I went too high on the second quench, I was reacting to the lack of color inside the foil on the normalization cycles.  I do realize this was a mistake.  Does anyone have any experience with the Brownells ATP 641 anti-scale coating?  I used this during the first quench and I am questioning if this prevented proper hardening.

Link to post
Share on other sites

 

4 hours ago, Joshua States said:

And if it's anything other than O1, AFAIK Parks AAA is a medium speed quenchant, probably not ideal.

I couldn't find any Parks 50 when I ordered the AAA, but now I see it is available everywhere so I just ordered some.  Thanks.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...