Jump to content
Sign in to follow this  
JohnCenter

Grinding after Heat Treat - Tips and Advice

Recommended Posts

Recently added a 2x42 grinder to my shop. Only has one speed (fast). But it is amazing at cleaning and shaping the blades after heat treat (compared to sand paper and muscle!).

Any tips or advice for post heat treat grinding (O1 if it matters) to be sure not to ruin temper?

Right now I figure steel changing color: really bad. And I grind with bare hands and never let the steel get too hot to hold.

Share this post


Link to post
Share on other sites

Grinding with bare hands, as you are, will alert you before it gets too hot as long as you are touching the area of the blade you are grinding.

The other big thing is to use a fresh belt.  Old ones create a lot more heat.

Share this post


Link to post
Share on other sites

That's pretty much it, never let it get too hot to hold in bare hands and watch the edge and tip.  I and most guys keep a bucket of water under the grinder situated so it catches the sparks and grit.  It also serves as a cooling dip between passes.  That is, grind until the blade is too hot for comfort (around 140-150 degrees F for most people)  then swish it around in the water until it's cool.  Wipe off, repeat.  The wipe-off is optional on water-resistant belts, necessary on others.  3M Trizacts, for example, are not in the least bit waterproof and will go away in short order if used on wet steel.  The Klingspor Zirconia belts I use for rough grinding don't care about water and can even be run wet.  The Klingspor gold J-flex belts don't much appreciate running wet, but they'll do it if necessary.  

  • Thanks 1

Share this post


Link to post
Share on other sites
1 hour ago, Alan Longmire said:

3M Trizacts, for example, are not in the least bit waterproof and will go away in short order if used on wet steel. 

How do they "go away"?  Does the abrasive disintegrate, or do they just stop cutting?  I bought some a long time ago because so many people like them.  I haven't had much success with them, but did run them against wet steel.  They still look ok, but your comment makes me wonder if water messes them up in a way that isn't obvious to the naked eye.

Share this post


Link to post
Share on other sites

Ive used a trizact to take about 30 blades from 80 grit to 220 or 320 grit (I dont remember what it is), I hand sand at 220 after that, the trizact still has 10% or so of its grit left. They last forever if you treat them right but if they get wet they lose grit very fast, faster than cheap aluminum oxide. You also have to be careful about sharp edges on the blade scraping off the grit.

The 80 grit I used was a worn down 3m brand, I dont remember what, but I used it with water until it broke at the seam. It was just fine for post hardening grinding when I ground on the wheel of my grinder, kinda slow on the platten but faster than a 1x30. Just some water dripping on the belt kept it cool enough that I didnt have to worry about overheating and I could grind faster and more precise because I wasnt constantly having to remove the blade to cool it. 

Usually I grind a steep bevel at the edge with the platten and get the edge straight then use the wheel to grind to the edge and then flatten the sides of the blade on the platten.

Wet grinding will get everything around you wet and if your eye protection gets wet you wont be able to see anything, but I think its worth it, otherwise you have to use a fresh belt every couple blades.

I tried running my trizact wet once and lost a bunch of grit but it worked fine after it dried out, I smack my blades on something to get off any water thats on it from cooling, you can get a little water on it, they probably dry pretty quick when running on a machine but I wouldnt try using a damp/wet one again.

Share this post


Link to post
Share on other sites

The adhesive on Trizacts is not waterproof, so like Stephen said you lose abrasive fast with nothing to show for it.  If you get wet spots you lose grit there, leaving a lumpy belt.

Share this post


Link to post
Share on other sites

I struggle with getting this right, will get a blue tip as often as not.

Also, except in the case of 5160 (and other through-hardening steels)  I don't get how people forge and heat treat these massively thick blades and then grind  down.....

I know FiF is not the gold standard but that's not the only example.

On this forum I was told 1095 only hardens about 1mm deep, so if you start with 6mm (or even thicker) my math tells me you should have unhardened steel by the time the bevels are ground in.......?

Discussed this with my mentor, but he grinds to final thickness and HT's in foil envelopes to prevent decarb, only sanding and edge bevel after HT.

Share this post


Link to post
Share on other sites

Gerhard reminds me of something I read on another forum: The blade might not be getting to hot, but the thinner edge could be heating and cooling faster than the worker is aware...?

But what about Scandsi? I've seen countless videos of makers finish grinding them to sharpness as well as sharpening them on belt grinders...

As a beginner I don't know... I just question and ignorantly speculate. It seems final grinding after heat treat is the standard, so maybe that speaks louder than 'theory'...?

Share this post


Link to post
Share on other sites

With regards to overheating, when finish grinding, I run the grinder fairly slow, with fresh belts, and the steel is always wet.  This allows me to have my thumb or fingertip right at the edge where it is touching the belt.  (I do sand my fingerprints off every now and then.)  Once it gets warm to the touch, I dunk it again.  Using this approach, I avoid getting blue tip, or spots along the edge.  I hardly ever use anything more aggressive than 120 grit after heat treating anymore, and final thinning of the tip is usually done with 220.  I'll use 300 grit to clean up the grind marks, and then start hand sanding after that.

Running slow (probably around 1000 to 1500 feet/min) with a good 120 grit ceramic belt, I get very little heating.  I can probably work the blade for 15 to 30 seconds before dunking in the water unless I am working on a very thin area.  The 300 grit AO belts cause the balde to heat up more quickly, and I have to be more careful at that point.

As with all things on the interweb, YMMV :)

 

  • Thanks 2

Share this post


Link to post
Share on other sites

I suspect many of those doing HT on a full-thickness blank are either a:) using a thin blank for a kitchen or filet knife to start with or b:) using a stainless alloy that has a high tempering temperature.  

I am probably the one who told you 1095 fully hardens only about 1mm (more like 1.5mm) or so from all surfaces, and that is true.  If you are doing a kitchen knife blank at up to 3mm thick, and doing a full quench without clay, you get full hardness since it comes from all directions.  There reverse it also true, which is why you get auto-hamon on shallow-hardening steels.

Finally, Brian brings up a very important point that hadn't been addressed:  level of finish before heat treatment.  This has a HUGE effect on what happens after HT.  I always finish things up to at least 400 grit before even thinking about heat treatment.  I also use anti-scale compound and/or a muffle tube with reducing atmosphere on non-axe objects.  This means there is no scale to clean up afterwards, and usually all that need to be done is a quick hand-sand at 400 and then grinding the final edge.  I don't do stock removal on hardened steel if it's not the best way to get the results I want.  I leave the edge thin enough that no more than a minute on a 400-grit belt puts the edge on, and go with stones and stropping from there.  

If you match the alloy with the quench medium and pay attention to atmosphere you can even harden a fully sharp edge.  I don't recommend you try unless you know exactly what you're doing, but it is possible.  The danger of decarb and warping/cracking is extremely high.  

  • Thanks 1

Share this post


Link to post
Share on other sites

I use a 24 grit 2x 72 pre and post quench....then a 50 grit...then a trizac 300,100,45,then 30. A scotch brite and a 2x 72 leather belt are on my to do list as well.

Its been my experience that the coarser grits build heat less quickly than the finer belts.

I leave my edge about the thickness of a dime prior to quench.....I don't see the point of going finer than 24 grit prior to ht/quench.

On thinner blades like 1/8 stock kitchen knives I will go thinner.....but not so thin that I see a need to use anything finer than 24 grit.

I don't hand sand or sharpen anything.....

  • Thanks 1

Share this post


Link to post
Share on other sites

I'm starting to suspect the digital kiln has done me more harm than good :ph34r:

My grinder/platen issues complicate matters, but I also know they use the good belts I don't have access to on FiF......

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...