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I have been researching fillet knives for a while hoping to find the perfect recipe for steel, geometry and heat treat.

 

Well I have found all manner of opinions and info but nothing definitive so I have decided to just conduct my own experiments.

 

I am starting to feel that blade geometry is the key and normalising a critical factor (I do 3 cycles anyway with every blade)

 

I have made some over thickness blades and grind after heat treat and some very thin and tried to quench with mixed results but have settled at this stage on this.

 

Yesterday I forged this blade from a very old rusty meat cleaver from under a farm shed (so just an unknown carbon steel) and forged quite thin (bit over 2 mill at the thickest down to about a mill at the tip)

 

I cleaned off the scale and did some rough profiling then did my quench as normal in oil. The blade hardened very well and a file scated along its length though I lost some to decarb near the tip before the file scated but I want the tip fine so that suited.

 

I got a better than expected slight bend in the blade but this came out in the first temper cycle. I clamped it to a straight bit of steel.

 

here is the blade after forging and rough profiling. Next pics are after rough sanding and quench. The flex pic is after the first temper cycle at 190 c and is at thickness described above.

 

I intend to do 2 more temper cycles at 200c and see how that is for flex and can then do some more post heat treat grinding after till I get the flex I want.

 

So where I sit at the moment (and it may yet prove wrong)is -  forge as close as possible to desired thickness then do basic profile and rough grind of bevels and heat treat as any other meat knife and then grind thinner if required post heat treat.

 

Anyhow for what it’s worth that’s my thoughts. I would appreciate any of your thoughts on preferred blade shape etc and if you have an opinion on the design re a curved blade or straight. Wider or thinner blade.

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That looks like a successful experiment. Only one test left to do and that requires you to go fishing......

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1 hour ago, Joshua States said:

That looks like a successful experiment. Only one test left to do and that requires you to go fishing......

 

Yep, one large barramundi is required for the next step!

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Posted (edited)

Yes Josh and Alan I hope to catch a Barra to test it properly but I seem to have lost my fishing mojo. I have been watching some YouTube on de boning chickens so that will  prob be the first test. Here is a pic alongside a Dexter Russel filet knife. I finished the last temper cycle and it has comparable flex so I am happy. Now to clean it up and handle it.

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Edited by Rob Toneguzzo

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Rob,good for you for picking on such a challenging,metallurgically,project,best of luck!

Your version looks good,though i'm not sure you're comparing it to quite a right knife(is that not technically a "boning" Dexter?).

But yes,they're similar in slender shape and certainly bendiness.

Dexter-Russel is a good bench-mark,an industry standard.

I use them primarily(mixed with Vic's)to fillet and process fish....Lots of fish...Big ones,mostly,but not so big either..

Frankly,that uber skinny-flexible:"filleting" knife has puzzled me always...Most fish in the world is processed using wider,stiffer knives...(i use butchers,for example).

I wonder what's going on there at your local seaside dock-what do commercial processors use?Or pros that fillet fish for charter sports?

.

 

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4 hours ago, jake pogrebinsky said:

Rob,good for you for picking on such a challenging,metallurgically,project,best of luck!

Your version looks good,though i'm not sure you're comparing it to quite a right knife(is that not technically a "boning" Dexter?).

But yes,they're similar in slender shape and certainly bendiness.

Dexter-Russel is a good bench-mark,an industry standard.

I use them primarily(mixed with Vic's)to fillet and process fish....Lots of fish...Big ones,mostly,but not so big either..

Frankly,that uber skinny-flexible:"filleting" knife has puzzled me always...Most fish in the world is processed using wider,stiffer knives...(i use butchers,for example).

I wonder what's going on there at your local seaside dock-what do commercial processors use?Or pros that fillet fish for charter sports?

.

 

Hi Jake,

Thanks for the feedback and reply. That is indeed a boning Dexter and is the knife I take out in my boat. It is the closest thing I own with good flex and I was aiming for similar but hopefully a bit better edge retention.It is a also what I have been using to fillet fish though they have been few and far between for me of late. 

I looked at the Wurstof and Dalstrong fillet knives but have only seen them on line . I have read some good reviews on them and thought I would try something similar to see if the shape worked any better for me than my Dexter.

That is a great idea about going to the fisherman’s wharf and will be what I do when next I am in Darwin. I will also let you know what they say.

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8 hours ago, Rob Toneguzzo said:

. I finished the last temper cycle

As counter intuitive as it may be, hardness does not affect flexibility. 

 

For example, take two fillet knives in 1084 with the exact same geometry. The one at 56hrc will take the exact same force to bend at a certain angle than the one at 61. The harder one will even bend further before undergoing plastic deformation. But the harder one will also be more likely to snap while the softer one takes a kink. 

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I'm watching this one with interest Rob.  I feel that fillet/boning knives are one of the handiest all around blades to have when processing meat at home.  If I ever get to the point where I make knives to sell, I think that they'd be one of the easier styles to turn over, depending on the audience that is. 

When it comes to blade shape, I think it's more dependent on what the knife is getting used for than anything else.  For large fish like your barramundi, or the salmon we get here out of the great lakes, a longer and wider blade with a gentle curve and good flexibility to it seems to be the preference of the guys that process a lot of fish.  For smaller fish I'm personally partial to a shorter, thinner, blade that is relatively straight and has an upturned tip.  Everyone has there own personal opinions and preferences, but I dont think that theres one particular style/length of blade that will work the best for all situations.

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Posted (edited)
3 hours ago, Joël Mercier said:

As counter intuitive as it may be, hardness does not affect flexibility. 

 

For example, take two fillet knives in 1084 with the exact same geometry. The one at 56hrc will take the exact same force to bend at a certain angle than the one at 61. The harder one will even bend further before undergoing plastic deformation. But the harder one will also be more likely to snap while the softer one takes a kink. 

Thanks Joel I agree about this and was a bit worried at 190c it might be a bit brittle for such a thin blade so I gave it two more at a tad over 200c

 

3 hours ago, Alex Middleton said:

I'm watching this one with interest Rob.  I feel that fillet/boning knives are one of the handiest all around blades to have when processing meat at home.  If I ever get to the point where I make knives to sell, I think that they'd be one of the easier styles to turn over, depending on the audience that is. 

When it comes to blade shape, I think it's more dependent on what the knife is getting used for than anything else.  For large fish like your barramundi, or the salmon we get here out of the great lakes, a longer and wider blade with a gentle curve and good flexibility to it seems to be the preference of the guys that process a lot of fish.  For smaller fish I'm personally partial to a shorter, thinner, blade that is relatively straight and has an upturned tip.  Everyone has there own personal opinions and preferences, but I dont think that theres one particular style/length of blade that will work the best for all situations.

Hi Alex thanks for your thoughts on this too. It is interesting you say about selling knives as I often get enquires about if I make fillet knives and if I get it right I might make a few to sell to put towards a long overdue decent belt grinder

Edited by Rob Toneguzzo
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Well guys I flew too close to the sun on this one.
 

Yet another entry to my graveyard of broken dreams.

 

I was cleaning up any scratches and decided to give it some flex testing which was easily enough for a filet knife but I pushed just that bit too far and snap!

 

This to me fully supports Joel’s ( sorry Joel not sure how to put those dots over the e in your name) comment that hardness does not effect the flexibility.

 

I had good flex in this blade and the gain structure looked good so that said to me the quench and geometry were ok but I feel where I failed was in my tempering - sacrificing durability for hardness. 
 

Instead of tempering at 200c I should have bumped that up to at least 220c or more. 
 

Anyhow back to the forge soon to make the next one.

 

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Just did a bit more research.
It seems that the Dalstrong Gladiator series fillet knife is 55 HRC and the Wusthof fillet is 58HRC so if the next one I make is out of 5160 to get approx 57 HRC I will temper at 260 C.

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Sorry,Rob,this sucks.It hurts to loose work,no matter how many times you do it...It was a really good looking knife.

 

I'm not sure if an alloy choice would get you closer to that flex/hardness/edge-holding ability combination that you're shooting for.

(or even maybe differential hardening is your friend here).

 

For utility strictly there's a trick used here locally where locals,when needing something with huge amount of flex,caeve it out of an old low-alloy carpenter's cross-cut saw.

Being decent carbon steel,and HT'd for use on wood, it has an ok performance and edge retention.Soft,but like old butcher knife type stuff,takes a very fine edge very quickly(and you carve it out cold,so don't have to do your own,challenging HT on such delicate section...).

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Thanks Jake, I may yet try that saw blade idea but I still have a bit of experiment left in me and it is becoming a bit of a personal quest now.  for inspiration I would love to see pics of any fish you guys are catching in your area.

 

The bridge down from me ( about 3 mins drive) is flowing after recent rain and I plan to get up early tomorrow and flick some soft plastic lures to try to catch a Barra. I have caught them there before at this time of year. then all going well I will give this fillet knife another go.

 

This is a pic of my best Barra so far ( about 15 years ago) though the fisherman has seen better days.

 

 

 

 

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Real pity about the snap Rob. Nice grain and nice fish though.

 

This was my best (about 12 years ago), a 31lb Fenland Pike. Sorry, it is a photo of a framed photo. Kinda ruined pike fishing for me, I’ll probably never get even close to this again.

 

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That sucks man :mellow:

 

I just wanted to tell that you can indeed lower hardness to solve this problem OR grind the blade thinner and keep the same hardness. Thicker cross section puts more stress on the steel as it bends. Had your blade been thinner, less stress would have been applied for the same bending angle so it would not have snapped. Two years ago, I made a small kitchen knife in 1095 tempered to 60hrc. That steel is known to have low toughness(around 10ft/lbs at this hardness), yet I can almost bend the last 2" at tip 90°. And it springs back perfectly straight every time. 

 

I think is was Don Nguyen who passed the ABS bend test with quite a hard integrally hardened blade that completely sprung back 100% straight. I've seen the video and it was quite impressive. The blade had enough hardness to give good yeild strength to the steel while it's geometry allowed a full 90° bend without putting too much stress on the steel. 

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2 hours ago, Charles dP said:

Real pity about the snap Rob. Nice grain and nice fish though.

 

This was my best (about 12 years ago), a 31lb Fenland Pike. Sorry, it is a photo of a framed photo. Kinda ruined pike fishing for me, I’ll probably never get even close to this again.

 

 

Thanks Charles...and wow what a fantastic looking big fish!

 

26 minutes ago, Joël Mercier said:

That sucks man :mellow:

 

I just wanted to tell that you can indeed lower hardness to solve this problem OR grind the blade thinner and keep the same hardness. Thicker cross section puts more stress on the steel as it bends. Had your blade been thinner, less stress would have been applied for the same bending angle so it would not have snapped. Two years ago, I made a small kitchen knife in 1095 tempered to 60hrc. That steel is known to have low toughness(around 10ft/lbs at this hardness), yet I can almost bend the last 2" at tip 90°. And it springs back perfectly straight every time. 

 

I think is was Don Nguyen who passed the ABS bend test with quite a hard integrally hardened blade that completely sprung back 100% straight. I've seen the video and it was quite impressive. The blade had enough hardness to give good yeild strength to the steel while it's geometry allowed a full 90° bend without putting too much stress on the steel. 

Thanks Joel, this really interests me and thanks for the info. I really do need to get a decent grinder asap.

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Wow,Rob,so that's a barramundi...Prehistoric looking beast,look at that tail...it's almost like it ought to have legs!

 

I'm ashamed to say i'm not an angler,and fish by  means much less sporting...:(...Mostly,King salmon early in the season,then Chum salmon later...3 other Pacific salmon are occasional by-catch,and so are several other species not related.

 

King salmon,with an incidental sheefish in a tub with it,and chum in the next photo...

 

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But all these get cut;first filleted:

 

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But that's just a beginning.Next comes the tedious part where the fillets get cut into thin,maximally even strips...(i've a problem with computers dying on me with all my photos in 'em,so couldn't find a photo of the cuts themselves:(...).

But this is the drying scene(why they're cut so small):

 

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It's a Lot of cutting...And each cut through very tough salmon hide,and against the wooden cutting surface...Serious knife freaks and makers all tell me i'd benefit from switching from industrial knives to some custom Unobtainium ones....i'm sure that they're right,but setting up the specialized sharpening scene is intimidating...

 

 

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Wow Jake I have never seen anything like that. Wonderful fish and The colour of that flesh is amazing. That’s a lot of fish. How do you eat it and how long will it keep once dried? Thanks heaps for showing that. I fillet my fish and then skin and crumb or batter and deep fry with chips is my favourite way but probably not the healthiest.

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36 minutes ago, Rob Toneguzzo said:

 How do you eat it and how long will it keep once dried?

 

Rob,i'll try my best at a brief,and least complicated explanation(it's actually a very complex scene).

 

There're two different kinds of cuts there in the smoker mixed up.(smoke,btw,contributes nothing to preservation,it's only to keep flies away).

 

The almost-whole width fillets with cross-cuts is "dia'gah",the way native people here dried their fish for the rest of the year(salmon only run for a few weeks in summer,but run in huge numbers,so this was The mainstay of diet,there's precious little else here.In spring,when dry fish ran short,many would die of starvation just because of this shortage).

Alaska is extremely arid,and once dry,fish or meat can store for a long time,but it starts freezing in mid-September anyway,so it's even handier.

However,meat is one thing,Fat being quite another.And we need fat desperately,it contains most of the more complex amino-acid chain segments;meat is only protein that humans,unlike say canids,are incapable of utilizing for this.

Fat doesn't dry.It goes putrid(polite term is "fermentation",but is not technically correct,being conversion of sugar,but here we run into unstudied complexities...).

Putridity,rotting,is what we call the process when assorted bacteria come and start decomposing matter into finer components.From this point everything becomes pretty variable...What kind of bacteria,how long they're at it,how we Like it(and Why,one of the unanswered questions...Palatability is a huge deal for humans,physiologically so).

 

So it all depends.I kinda "study" this stuff,have been for quarter-century,and there're few if any clear answers.

 

Native people here used no salt(which is it's own kind of fermentation process btw),and dia'gah is very challenging for me to make.

But it does keep indefinitely,becoming more stale,and at times even mouldy,but changing gradually all the time.

I mostly freeze it as soon as it's "ready"(another uncertain term...).

 

The long thin strips is a Scandinavian product,introduced here by gold miners a bit over 100 years ago(Alaska is just like Australia in that sense,only even newer,first white interloper up my drainage for example was russian half-breed Glazunov,in 1827).

 

This is in contrast a complex form of salt,And fat,preservation.After "drying"(King salmon is so greasy it can never really be said to "dry"),it was packed into oaken casks,where the oil rose up to cover the fish,and acted as preservative.

This i've actually never tried in that purely traditional form,and not sure just how stale or sour that fish oil may've gotten by the time weather turns to freezing.

I also terminate these processes by simply freezing.

Frozen,this stuff doesn't last forever,either.It's hard to package hermetically,and keeps on getting staler and drier("freezer-burned" in local usage).

In general it works to keep it till almost the next fishing season,any longer and it may affect your fishing luck....

 

I'm not(i hope)being so long-winded because i'm a freak...It really is an infinitely complex,organic system(-s),flexible,ever-changing,rooted in some intensely complicated issues...

 

All over the world Every culture does something of this kind.Cheese,cultured sausage,wine,bread even,and many,Many other ways to take advantage of that symbiosis we have with ambient aerobic bacterium.... 

 

I fillet my fish and then skin and crumb or batter and deep fry with chips is my favourite way but probably not the healthiest."

 

I totally relate!I think it's the best,and can be just fine if the grease is of a good sort.Often a big sheefish here would have enough fat around it's guts to almost fill the frying pan to overflowing...I use it to do just what you say,(if often too lazy to bread it...:)

 
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That blows my mind. What a process and you would have to get it right as there is such a short window of opportunity to catch those fish.    We can catch fish all year round but the fishing gets better during the build up before the wet season though it is uncomfortably hot and humid. I have seen where bears eat those fish when they come in great numbers but had no idea they only came for a short while.I really appreciate you taking the time for that reply

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Found this old bread and butter knife in a second hand store - no visible makers mark. Someone had sharpened it.

 

It takes and holds a great edge, flexes like an acrobat and returns to straight . They don’t make them like that today. If all else fails I will fillet my Barramundi with it.

 

Anyhow forged up another today out of 1075. Here is a pic as forged. I left the handle oversized but will refine it in profiling. I tend to make handles too small.

 

the starting stock was 4mm thick and I forged the blade to 2mm with a slight distal taper in blade and tang. no bevel this time I will Ryobi that in after heat treat all going well.

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Well it looks like success.

Heat treat went well with just a slight bend which came out in temper.

I did 3 cycles At 220c. 

The blade spine is 1.7 mm tapering to .7 near tip and has good flex but not too much. I still have to grind in bevels and clean up but happy.
 

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Final straightening as it had a slight kink still 3/4 of the way near the tip.

 

I just clamp against the rest of the 1075 stock I forged it from and used some aluminium foil to shim and clamped 

 

bevels ground and now just to clean up with hand sanding then handle and then to find a Barra.

 

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Wow, Rob, that thing looks wicked!  Nice job.

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Probably not the biggest but definitely one of my favorites. This was 6 years ago. Back in my bow fishing days. Just a big ol nasty carp!!!

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