CRAZY theoretical idea from the uninformed for makers.

Walking Man

Walking Man

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Recently I read that in order to drill a hole (ie spyderco style) in a hardened blade, it is best to blowtorch the area to remove the temper. (Hope I used that word right)
If someone were to take this process one step further - Would it be possible to differentially untemper a blade in this manner to get extra strength?
If this is possible, Why hasn't it been done before?
and make sure I get the credit.... :D
thanks.
 
If you heat a blade too much you lose the edge holding ability...the tradeoff between toughness and edge holding is the fine line that knifemakers are treading at all times. Complicate this with the fact that each blade material has its own characteristics or toughness and edge holding and you have the knife industry in a nutshell.
 
From what I've read, and done, its pretty difficult to spot anneal the high alloy steels commonly used today. Simple carbon steels aren't bad but the new wonder steels just don't work out that well.

Its not difficult to ruin the heat treat/temper by heating them up, but you don't necessarily get them to an easily workable state, and its not easy enough to isolate heat that intense onto one part of the blade to get an effective differential temper.

You also run into decarb and other problems like warping when heating steel.
 
Torch tempering a hardened blade is an old technique. You clean it off so you can see the colors as it oxidizes, then slowly "paint" the heat along the spine until you get the "color rainbow" you want. This is a gross oversimplification, and it is extremely easy to overdraw the blade. Some dip the edge in water, heat the spine; alternatively, use heat trap paste. It is sort of the opposite of claycoating while hardening.
This technique, along with using a hot steel plate as the heat source and setting the spine on the plate, was a common method in the 80's and before, prior to the popularization of the edge quench.
There has been commentary that the torch technique does not heat deeply enough into the steel to draw the temper on the core without spreading it too far down into the edge.
As mentioned, it won't work as well with high alloy steels because the metallurgy is such that it is designed to rapidly dissipate the heat through the entire piece.
 
Stainless steels don't differentially temper very well. I hear that Paul Bos has done it a few times but it wasn't easy or worth the effort.
Because most of the stainless steels are air hardening, heating it with a torch may even make it harder than before. Even if it didn't make it harder it would still be hard to contain the heat on the spine for the long soak times needed with stainless.
 
This idea has been around for a while. I know a guy who "softens" the spine of knives made from files/tool steel by torching the spine of the blade while the edge is held in water. Takes patience, but can be done.

Now, your everyday folding knife doesn't come with a blade made of O-1, etc. :rolleyes:

Still, though, it does have its useful application in turning old tools into knife blades.
 
If your intent is to drill a hole in a hardened blade you can use a sharpened masonary bit. You will be restricted to 1/8" diameter as anything larger will fall apart due to the heat generated. Buy as many brands as possible, some hold up far better than others. Use high speed and quench the drill tip in cutting lube. Don't try to drill through in one go.
I know of many Boker blades that have been drilled in this way. You should get 5 or 6 blades drilled from one bit before it dies a horrible death. Please wear saftey glasses.
I have no idea why anyone would want to drill a hole in a Boker and what the hell are these springs for?
:D
 
I have and do now, differentially harden stainless as in 154CM , ATS 34 air quench steels the way I'm testing
you need to insulate the spine and be very careful with a
acetylene torch
I'm still testing before I sell any of
these blades but it's looking good..some of the guys here have or have tied this one way or the other but I'm not sure of their
results
if it's done differentially (hardened) or not?
that's the way I'm doing it (other then another way I'm trying to be posted later),,


I've been hardening High carbons with a touch for many years so that helps...
but to try and temper differentially you will have a problem with the air steels
this is to say the easiest way is to differentially (harden) then temper
 
Pete is right about the masonary bit. Another idea, go ahead and get a carbide bit. It will do the job. I suggest, DO NOT mess with the blade temper unless you know exactly what you are doing. Your intended purpose is to drill a hole, not screw with the temper.
 
masonry bits are fitted with carbide and will bite the steel
real bad as you punch through the pitch (angle)is not made for steel.

spyderco style holes are good size holes,
if use try to drill with masonry bits or even carbide bit on a short hardened blade
hang on because you'll need to. :eek: clamp it down and stand back dude...

if this is what you want to do..
your best bet would be, have a machine shop mill it out, with a
carbide or cobalt end mill just 2 cents don't get hurt...
:(
 
There are high tech methods of drilling holes such as EDM, ECM and others that would be far easier than carbide drills.
 
Originally posted by Peter Del Raso

I have no idea why anyone would want to drill a hole in a Boker and what the hell are these springs for?
:D
Click to expand...

A little tiny hole, a piece of wire could fit through? Probably a back up pivot hole. ;)
 
No, not about Peter DelRaso's quip about the spring and the extra holes. I meant about tempering ??? untempering the hole around a Spyderco opening hole.

Is your idea that the hole creates a lot of stress and brittleness in a blade that could be stronger without the hole ? And if there is a hole, tempering the area around the hole would reduce some of the stresses and get better toughness ?

I'm just guessing, but my response is related to that.

#1 - Spydie type blades, with hole or not are pretty bloody strong and won't break unless you are wanting it for a prybar.

#2 - as mentioned it can be difficult to differentially temper a high-alloy blade, and even more difficult to do it accurately on a blade as small as a Spydie's. The high alloy steels may also not respond in the manner you think. Heating up a small area may result in additional hardening if you hit a secondary hardening temperature.

#3 - it may be pointless. The properties of high-alloy steels like ATS34, BG42, VG10 and D-2 is that both hardness, edge holding and toughness to a degree reach an optimum level and particular levels of hardness. I can't give specifics but high-alloy steels don't necessarily obey the simple law of hard = brittle and soft = tough. That applies beautifully to plain carbon steel though.

I understand your thinking (if I'm right about your thinking) 'cos thats what I used to think. Then someone set me straight. Jason.
 
Walking Man,

Are you making a knife or modifying one that is already hardened? Cause otherwise, I would say hole-first, then harden is always the more painless method. If not, than I second the notion to use carbide/masonry bits.
 
You guys have got me wrong.
In the title, I typed theoretical, and that's all I meant.
I have never drilled a hole in a blade, and at this time, I do not plan to. I don't even have tools to do so.
*What I was thinking is that many folks really like differentially tempered blades, right? So the heat treat only hardens the edge, right?
So, when I read that someone (probably more than one person) was able to soften an area of the blade to drill a hole that got me thinking.

So the question that followed was: Would someone be able to dramatically speed up (and reduce the costs involved) the differential tempering process by hardening the whole blade and then softening up the spine area.

Sounds crazy. Maybe. You're the experts, I'm really just a beginner.
BTW some of you guys really lost me with your technical info above.
 
So the question that followed was: Would someone be able to dramatically speed up (and reduce the costs involved) the differential tempering process by hardening the whole blade and then softening up the spine area.

yes, some do that. but generally only with high carbon steels like O1. i believe its called drawing the spine of the blade. its a bit risky if you dont know what you're doing. (you can ruin the edge)

the super alloys that the majority of nice manufactured knife are either not possible to differentially harden or they are cost prohibitive to.

that answer it?
 
yes that would be it, differentially tempered
but at 62 Rockwell I personally think that is way too hard
to easily sharpen in the field.

wow I'm thinking a really rough
hollow grind on that knife, for High carbon
( thinking rusting problems)
but they're the ones that have to worry
about getting repeat buyers.
:( just my 2 cents
 
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