How far before heat treat?

[imskippy]

Hey guys just looking for a rule of thumb here. How far do you work your blades before heat treating them? do you shape and grind all the way to the edge or just get them close and finish up after the temper? Also what about the overall finish prior to treat aswell? Just working on a few blades from a sawmill blade and wanted to know what the "pros" do. maybe some pics if anyone has some at that stage. I'm doing a scandi type grind on these kinda like Robtattoo's grinds and sticshooters recent bowie. Thanks Skippy

[Steve Nuckels]

Good question!  I'm watching this close!  

I take my edge close to finish edge, just short of final sharpening!

I was considering leaving more material than usual on my current project to try a smoother final finish on the blade, I usually end up with a interesting texture like damascus.

[Lin Rhea]

Take the blade to 80%-90% shape and to about 220 grit finish. Leave the cutting edge about the thickness of a nickle till after the quench. I like to get the edge, again as thick as a nickle, pretty smooth and slightly radiused. This helps prevent cracking in the quench. In other words, deep scratches across the edge can provide a place for cracks to start. The blade can be under a lot of stress during the quench, so a little extra precaution is worth the effort. Lin

[Lin Rhea]

As a rule, the longer/larger the blade, the thicker I leave it during the quench, because of the tremendous stress it is under. Again about the thickness of a nickle. If it's a hunting knife, I can take it down to about a dime's thickness.

Steve, If you leave it slightly thicker for the quench, you can remove all the rough stuff and have a good finish. Allow material to remove. Just dont get the balde too hot while finishing. Lin

[Steve Nuckels]

Thanks Lin, your so genourous with your knowledge!

Steve

[chiger]

Hey Steve,

I do pretty much as Lin said.  I'll leave it about the thickness of a dime on smaller blades and a nickel on the thicker/bigger stuff.  On stock as thin as a saw mill blade, it might be closer to a dime though.  If you're talking about a band mill blade.  

I too sand um to at least 220 grit before heating and quenching.  Maybe to 380-400 on thick blades with deep hollow grinds.  For most shapes you don't need to go any finer than 220 though.  But you do need to make sure you get any scratches that are courser than the 220 grit out.  Lin ain't kidding.  Quenching steel is a very violent process inside the steel!  

Oh, and he's right about rounding corners, like where the grind mets the rassco and the tang shoulders...that sort of thing.  Those really set up stresses in quenching.  Plus a sharp angle will break and fail quicker than a round junction.  

That, I found out the hard way!  GRRRR!

[skullworks]

Great info from the pros! Thanks guys!

[imskippy]

Excellent info Lin. Thanks for sharing your knowledge with us wanna be's. Would anyone car eto share pics of their work at this stage? Skippy

[kbaknife]

Lot's of info on this:
Also keep the 220 or higher "scratches" running lengthwise with the blade - don't have any running across the blade.
When the steel goes through the high stresses of forming all of these different "-ites", from perlite to austenite into martensite, which can sometimes happen in only milliseconds, sometimes longer, it's an atomically violent transformation. Perlite, austenite and martensite are different sizes! If that transformation of expansion and contraction occurs in a tight spot, like a sharp 90 degree corner or a deep scratch, it can actually seperate the different plates in the steel and create a tiny little "CRACK" that can't be seen by the naked eye until too late. Sometimes, on the other hand, you can end up with two pieces of steel when you only started with one! Oops!
Listen to Lin. Don't get it too hot during hardening!
Heat is your friend, or your enemy.
Learn to make friends with him.

[tippit]

I also do about what Lin says.  Out of experimenting, I've tried to see how close I could get to being finished on the edge.  When too close the blade edge will usually warp as apposed to cracking for me anyway...tippit

[Jeremy]

I'll weigh in for no other purpose than to drive home the point  

On hunting knives I'll leave the edge the thickness of a dime before hardening.  Larger knives get left a little beefier still.

I normally go to 400 grit with all corners and edges rounded off.

[loyd]

those warped edges can be a heart braker after 2 hours of grinding and polishing. just makes you want to throgh somthing. loyd been there and done that

[sticshooter]

Now ya guys decide to tell me this stuff! But I never payed to much attention to this detail. and only had 3 crack a bit when quenched. But I will a start paying better attention to this from now on.<><