grinding pre/post hardening?

T

trogdorr

Joined
Jan 3, 2015
Messages
84
I am relatively new to knife making and I have a question about whether or not you should heat treat your blanks before grinding them? For my last couple of knives I have been using farriers rasps which I flattened the teeth, annealed, shaped into a blank, ground the bevel, then heat treated.

My thought process is that it is going to be a pain to grind on hardened steel and I should take advantage of the blanks softness while I can. Is this correct? Is there an advantage to heat treating the blank while it is still uniform in thickness? I realize that thinner metal will get hot/cold faster than if it were thicker metal. How much of an affect might this have on edge retention since the edge is cooling faster than the spine on its way to the quench bucket?

Any little nugget of information about the steps you take to make a knife, or the heat treating process, would be much appreciated.

Thanks for your time,
Trogdorr
 
As a beginner, I'll assume with limited tools, I'd do most or all pre heat treat.

I am the exact opposite of Don in that I grind after HT because I hate grinding soft steel! :)

With good equipment grinding after HT is a breeze. I prefer it because there's more tactile feedback and easier "steering", less gauging with rougher grits, and less chance of warp during heat treat.

Many guys will do grinding before AND after. I personally have no desire to do the same job twice.
 
Hey Trogdorr
Ditto on Don's comment for me too. I usually try and do most of my grinding up front (prior to HT), but after Joe's remarks, I think I'll give his method a whirl to see how it goes.
 
I almost always grind my steel post HT. Everyone has their preference but I just hate grinding the blades twice.

Here's some pros and cons

Pre HT
pros
fewer sparks
easier on belts
less pressure needed
easier to get a really high grit finish (If you don't plan on grinding post HT)
Cons
You have to finish the blade to at least 120 grit, then grind it again post HT
Makes blades more prone to warp
You can easily bend thin blades


Post HT
Pros
1 step grinding.
Thin blades wont bend
less likely to warp
You can keep HT'd blanks in your shop and finish them whenever you like.

Cons
Tons of sparks
harder on belts
harder on the body as you have to apply more pressure
 
I've only ground W2 and AEB-L. W2 was done mostly preheat treat and AEB-L was done post heat treat. With my limited experience so far I prefer the stainless post heat treat.
 
I prefer to grind pre-ht, and doing only surface touch-ups post-ht to get rid of decarb if present and to get a nice finish.
I only do hand sanding or water cooled belt sanding after ht. Belt heat treatment is a no-no. ;)
 
I grind my blades down like Don does + I hand sand them before heat treating. I usually edge quench, thus a good portion of the blade remains relatively soft.

I have to hand sand again after heat treat, but the hardest hand sanding post heat treat, is the edge. Usually, the unhardened portion of the blade is quite easy to hand sand after heat treating. This is because it is at 400 grit or so. My grinding post heat treat is isolated to just the bottom third of the blade.

Geometry plays a big roll in how much you have to grind after heat treat too. I take the edge down to .030 - .040 before the big dip. And I use a beefy aluminum quench plate to keep the quenchant where I want it.
 
Thank you for your replies, Its good to know I'm not alone in my methods. I have been using old motor oil as my quenching liquid and it leaves this layer of gunk on the surface. It darkens pits left by file teeth of the rasp and I really like how it looks, but its hard on sandpaper and takes a while to remove. Any comments?

-Trogdorr
 
why is that? I've heard that the used oil adds carbon to the metal, not sure where from, but up until I read that that was my understanding.
 
trogdorr said:
why is that? I've heard that the used oil adds carbon to the metal, not sure where from, but up until I read that that was my understanding.
Click to expand...

No, that's all wrong. Short answer is the hot blade is not in contact with the oil long enough to pick up carbon. And why would a smith want to add carbon to a high carbon steel anyway? :cool: Used oil is just nasty, carcinogenic & probably the wrong speed for a quench oil.
 
According to YouTube, knifemaking equals railroad spikes, magnets, bbq grills and motor oil....:grumpy:
Thank the gods for Nick Wheeler, Kevin Cashen and Bladeforums, eh?
-Mark
 
Emerson knives grinds all their blades after HT, but they have production machines setup
I just saw a video in the Bark River shop and they also grind post HT on Burr Kings,
that said, the 3 knifemakers I've visited do partial grind first, HT and then final grind post HT.
 
Interesting- for me, it all depends on how thin the stock is. A .070 or thinner blade will usually cup and warp during hardening if ground pre-HT, but 1/8 and over rarely do. OTOH, I do fairly wide blades- this may not be the case with penknives and such.

Operator error, perhaps, but it works for me, and there's not that much material to remove from a blade that thin- the only caution is overheating.
 
Last edited:
trogdorr said:
That is good to know. I've heard of it done with water also, how well does that work?
Click to expand...

Water is too fast for most high carbon steels and blades will crack. It does work with the right steels, but the learning curve is steep. If a person doesn't want to get 'real' quench oil, canola is the next best thing...
 
You must log in or register to reply here.
Back
Top