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fillet knife blade's geometry?
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fillet knife blade's geometry?
In rec.knives
wrote:
Sorry for the late reply, I've been away from my computer for a
while,
That's ok, some of you actually have a life away from newsgroups.
All I know is that you get a nice flex / resharpening frequency
with a 56hrc blade and the 63hrc blade snapped when I tried
putting a 9 inch blade to about a 45 degree flex.
If Del breaks the sucker, that's his problem.
But that isn't the question anyway.
What geometry would you suggest in a fillet blade?
Was the blade that you broke "full hard HSS" made from a power
hacksaw blade?
How thick and how wide was the blade on that broken blade?
Was it a forged blade heat treated by a bladesmith?
I have a full-hard tungsten HSS hand hacksaw blade here that can
flex more than 120 degrees. No kidding on any of that. The back
of that sucker absolutly cannot be filed. It's made in Sweden and
brags on the fact that it's tungsten HSS (and spark tests right).
The tungsten based HSS's are considered to have slightly less
strength and only slightly better edge holding.
So here we go again
the flexibilty of the steel has mostly to
do with cross section.
The 63hrc blade does make an exellent trout knife, it doesn't need
to flex like a fillet knife does,,, so if you can accurately
temper (draw) it back, yes the power hacksaw blade will work
great.
Have you "drawn the temper back" on HSS like that before?
If you are grinding it clamped to a board you most likely are
getting the blade hot enough to be drawing the hardness down a bit
anyway,, but you have to be real lucky to be able to do it that
way consistantly without burning the blade, although soaking the
board with water might help a bit as a heatsink.
I grind mine held in my bare hands with the blade supported with
my fingertips so when I start at 63 or 65rc I finish at the same
hardness because my fingers won't let me hold onto a blade much
over 200degrees F. (it's a very slow prossess)
Oooo... what you just wrote is perfect for hardened carbon steel but
is not needed for HSS, it can handle the heat.
It takes 40 hours at 1200F for M2 HSS to be drawn down to 45hrc.
It takes 100 hours at 900F for M2 HSS to be drawn down to 64hrc.
That ain't a typo, Page-689 ASM's Tool Steels 4th Edition.
When I read "full hard" in the first post I thought you meant to
leave it that hard so I may have miss-read your intent.
Happy grinding,
Bear
Yes, we're completely knuts
that's the whole point of making it
from a power hacksaw blade. The steel has already been heat treated
to high strength and at its best edge holding hardness by the
factory.
We want to use their heat treating knowledge and expensive equipment
to our advantage, even if it's just to cut up a stinky old fish.
That's why we're called "knife knuts"? :/
I'll catch back up with you in a week,, the ice just went out of
the lake my parents live by this past week,, I'm after some of
those 2 pound crappies so I can test out my 10inch fillet knife.
Cool.
Get back and tell us about it.
Compare this...
You've done enough hand hacksawing to know that a carbon steel
hacksaw blade with teeth at about ~65hrc will wear out pretty
dangged quick. And a high speed steel-toothed saw blade at about
the same hardness usually gets changed out when you get tired of
a kink in the blade, not because it quit cutting.
Am I anywhere close to your experience on that?
I've got several brands of all-hard (full-hard) hand hacksaw blades
around here and they are a hand-hacksawer's dream, they don't kink.
You push them hard enough they'll break.
If you push "un-breakable" type (carbon steel, or bi-metal or
"flexible HSS") hard enough it would break an all-hard one, the
un-breakable type would kink to beat heck and be ruined, anyway.
IME, the un-breakable type are weaker than the all-hard breakable
type. YMMV
Metallurgy theory agrees with me on that, BTW.
The all-hard ones cut straighter, in my expereince, it's true what
they say about the all-hard hacksaw blades cutting straighter than
the "un-breakable" kind. No kidding, see for yourself.
We (knife knuts) want to take advantage of the extra edge holding
ability HSS has over carbon steel at 65hrc. HSS holds its edge 5
to 7 times as long as high carbon steel at 65hrc according to
industry's sales pitches.
But knife blades aren't 65hrc from the factory, right?
They aren't hard like carbon steel taps and hacksaw blades, like
you're used to working with, they are much softer than that.
I drew the temper on a couple plain carbon steel hand hacksaw blade
to soften them up like a custom knife (~58 hrc) not as soft as the
typical factory knife. Yeah the factorys say they are that hard
but they weren't counting on you having access to a $10,000 Wilson
hardness tester, now were they?
It's to their advantage to fudge-toward the soft-side for production
reasons when they're grinding 10,000 knives per hour.
Ok, enough BS about the "about right for a knife blade is 58hrc"
knife magazine bull****, the ~58hrc carbon steel saw blades were
-forced!- to cut though 1/4 what the factory-hard ones would cut.
What number-value a guy could put on that is up for grabs, I put
"at least 4 times" but right away the ~58hrc ones didn't cut worth
anything.
Can you imagine drawing all your carbon steel taps for an hour at
525F so they'll "be easier to re-sharpen" -as sold to you- in the
knife magazines?
Until you get used to knives for certain cutting tasks that are hard
like a tap or hacksaw blade teeth, then you just don't know the
magic of them.
The extra hard knife blades cut into stuff that the soft ones won't
because the soft one's edge rolled so quick, you didn't really get a
chance to evaluate the original edge.
No kidding on that.
It's not just "edge holding" it's "cutting ability" or "edge
integrity" that makes it cut so extra good and keep cutting.
I'm not saying you can get this from a newsgroup post, it's
something you have to experience yourself to really get it.
Alvin in AZ
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