Have I been doing this wrong?

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paintfool

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Sep 7, 2004
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I have been grinding my blades and finishing them to about 600 grit before heat treating, the edges are pretty much ready for the final edge bevel (pretty thin) but I just got Bob T's book and he heat treats right after the profile is done and then grinds the bevels hard.
I've seen a lot of guys doing it this way and then I've seen some guys take it to almost a finished state before treating...
is there a right/wrong way to this or is it just personal preference and experience?
I am using 440C 1/8 thick falt, and was planning on a salt bath for treating, the bath fell through so now I might have to use an oven, but the blade might be to thin and warp on me :(
should I just profile the blade then heat treat?
what is too thin for an oven as a general rule??
TIA, Worried Steve lol. :eek: :D
 
Several makers grind their blades after heat treating. It all depends on how many belts you wanna go through. I grind mine before heat treat, but do not go very thin, as I don't want to encourage warpage.
 
the knives I have on the go right now have short bevels, and that bevels is ground down to about 1/16th, the rest of the blade is pretty much still at an 1/8" aside from a shallow false edge or something like that.
is 1/16" on the edge asking for trouble?
 
Danbo said:
Several makers grind their blades after heat treating. It all depends on how many belts you wanna go through. I grind mine before heat treat, but do not go very thin, as I don't want to encourage warpage.
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As you know Dan, warpage is only one of the problems that can result. Unless you have a very good heating system, a thin edge will over heat very quickly, resulting in carbon loss and grain growth at the most critical area not to have either. I have found grinding hardened steel can keep zirconia belts going a little longer than I expected them to, most likely due to the fracturing affect on the particles. But I also found some serious problems with stress issues from heavy grinding after HT. This may not be as evident with shorter blades but becomes very obvious with swords, and of course extra care must be taken to never let that blade get hot on the belt.
 
Kevin R. Cashen said:
As you know Dan, warpage is only one of the problems that can result. Unless you have a very good heating system, a thin edge will over heat very quickly, resulting in carbon loss and grain growth at the most critical area not to have either. I have found grinding hardened steel can keep zirconia belts going a little longer than I expected them to, most likely due to the fracturing affect on the particles. But I also found some serious problems with stress issues from heavy grinding after HT. This may not be as evident with shorter blades but becomes very obvious with swords, and of course extra care must be taken to never let that blade get hot on the belt.
Click to expand...

that just about proves and adds to my point that steel has stress at any given time.
it's just equaled through out the steel when stress relieved
yes in a way you stress relieve but mostly you're equalizing the stress though-out the steel.
you'll find this out even grinding cold on a surface grinder, it will warp
if you don't take care in the amount you take off each side..
and this can be with dead soft or full hardened to tempered..
some one tell me I'm wrong and then show me why.. :D
 
I can't push her any more captian she's gonna blow. :eek:
paintfool be very carefull with thinning the blade to much before heat treat. About the only to find out now is to do it. I had a couple of blades warp on me durring the quench last week. :mad: I'm sure they were to thin.
Lesson learned.

Joe Foster
 
If you have been finishing to 600 grit before heat treat and like that preheat treat finish that is fine. When asked or when sent to me for heat treat I suggest stopping at 400 grit.

As for warping: It is most largely a function of quench. An often neglected step that can help minimise warp is preheating. Preheating can minimise the occurance of conflicting expansion and contraction within the steel during the austenitizing soak. I usually ramp moderately to preheat and hold there for about 7 minutes, then ramp as quickly as the furnace will to austenitizing.

As for your salt pot: I do hope it was the deal for it falling through instead of the molten salts :eek: .

RL
 
LOL I hope that's not the reason he stopped either! hahaha
naaa I was planning on sending it away to Brian Lyttle but he stopped doing stainless in the salts :(
hopefully I can get it done through Jeff Diotte now, who sends them to allied HT in Ontario. ;)
 
Always leave enough thickness to grind off the decarb and get to the good steel.The thinner it is the more it decarbs.
 
Is decarburization an oxidative process? IE, does carbon form CO or CO2 and off gas or just what? If so, then the less oxygen the less decarb, and hence the less scaling at the edge.

A little trick I read long ago: almost all stock removal makers profile at least some with a grinder. A lot do this by laying the blade on a workrest, creating scratches across the edge. Always do a pass lengthwise along the entire profile so the scratches follow the edge. If I remember correctly, it said that cross-scratches act like little hinges that allow the blade to warp more readily, whereas the longitudinal scratches actually strengthen the edge the way corrugate increases cardboard strength.

Now, that may well be urban myth, but it's of such little difficulty I do it routinely.
 
I'd guess it is just more knife maker romantisisam. Although it does stand to reason they would harden faster in the quench than the steel body. So why not. It sure wouldn't hurt anything.

RL
 
Yes,decarb is an oxidation process.However it will happen to some degree in any oven ,regardless of how well you wrap it.Salt pots are another galaxy away from ovens -oxygen free (virtually).Salt pots are to ovens as anti-matter impulse engines are to jets.
 
I'd like someday to have one for quenching. As I do quite a bit of stainless it doesn't look good for me having one to austenitize with. Anyhow, where I am is not at all safe for any salt pot :grumpy:

RL
 
I usually take mine to 400 before quench, and leave the edge about 25 thousandths. I smooth and round the edge a little before HT, thinking I'm avoiding heat risers from deep scratches. I also normalize at least three times before quench. Since I've been doing that I have very little trouble with warping. The hard part for me is getting the forge temp low enough not to decarb the edge, like Kevin said. I put a 2" pipe, capped on one end, inside my forge. That seems to even out the temp a bit but I still have the issue of heating the edge much faster than the rest of the knife. I'm slowly learning to keep the forge at a lower temp. Meanwhile, I watch the edge for critical and quench when it's ready, not holding out for the whole blade to come up. Seems to have improved my results but I'm sure not there like I want to be yet.

I gotta get that salt pot built! :rolleyes:
 
does anyone have any links to a salt pot setup?
I'd like to see one.
and just how dangerous are they?

I think Allied should be able to do a good job, they do lots of blades from what I hear.
 
Dave, is the pipe going to work out for you OK? I should have had it threaded for a cap on one end. I guess you could have it welded, too.
 
Yeah it is John, my biggest holdup right now is finding the right thermocouple. I have a guy who'll weld it up for me. You are the man, but who knows it'll probably take me two more years to get this thing actually done... :rolleyes: :D
 
man the pics and warnings in the 3rd link are nuts!
I don't think I will be trying that anytime soon... :eek:

Thanks for the Links! ;) :cool:
 
Yeah,salt pots are a lot like anti-mater in that way too.Very unstable if a bit of foriegn matter get in them.They must be treated with great respect and caution.
 
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