grinding after heat treat?

hardheart

hardheart

Joined
Sep 19, 2001
Messages
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After grinding a couple rough knives from hss power hacksaw blades, removing considerable amounts of M2 after HT seems like a bad idea (if going from 1/16" down to ~.025" is considerable:confused:) I know machinability varies greatly among steels, but are there some which can be hardened before being ground at all without wasting lots of time and abrasives, or worrying terribly about the hardness getting screwed? Chuck Stapel makes a knife while you wait, according to his site, from hardened steel. http://www.stapelknives.com/latest_news_ki.htm
A small skinner with a Micarta handle can be turned out in a couple of hours. He starts with a piece of heat-treated steel, then shapes, grinds, drills, clamps, cements and sharpens the small knife while you watch. ...The current design features a 3 3/4-inch blade of high carbon steel...
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Also, Sal Glesser mentioned in a recent thread how some steels have to be ground before HT, which kind of read to me like Spyderco manages to grind several after HT. http://www.bladeforums.com/forums/showpost.php?p=4252198&postcount=1

We would cut them out, heat treat, tumble (cheap), grind, sharpen and ship. Some steels have to be ground before heat treat.
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Plus I see questions about how thin a knife can be ground before HT, which I don't completely understand. Is this just because of using a forge or torch for austenizing, and having a harder time controlling temp? If a controlled oven or something like salts were used, would it still matter how thin the blade was ground, or is it then more of a concern with quenching speed? I would guess that could also be dealt with somewhat by using the same temp controlled devices to gently lower the temperature considerably from the austenization range to Ms (marquenching?)
 
I don't have a lot of time at the moment so I'll give you the nickel version.

If you keep the edge temperature of the knife at or below the tempering temperature for the particular steel the blade is made of, no detremental effects will occur during grinding (well none that are heat related). Some steels are hot work steels and tempering temperatures may approach 1000degrees F with working temperatures on some in the red range! Most of these steels will also be a bear to grind even at these temperatures.

Generaly speaking thin blades are easier to warp than thick ones. Plate quenching of air quench steels gives mechanical support to the blade during the quench and helps eliminate warpage. An even symetrical grind and even heat removal during quenching is essential to eliminating warpage. A plunge quench is usually more forgiving than other methods of entering a liquid quenchant.

Hope this answers some of your questions.

Jim Arbuckle
 
I have made fillet knives out of power hacksaw blades. As long as you don't get the blade hot enough to change the temper you don't need to re-heat treat them. They were very though on belts and are probally a Rc of 62 or so but hold a great edge with minimal sharpening. I basically put a convex edge on them and they were good to go, they were only 1/16 thick.
 
So is grinding after HT for most knives an uncommon thing, outside of creating the desired final finish? Do fillet knives generally have to be ground after the steel is hardened because they are so thin?
 
Grinding after HT is not uncommon. It's often the preferred order if you're using the big CNC flatgrinders used for production knives.
I don't notice a whole lot of difference on grinding with the new, quality belts. Just have to keep things cool while doing it.
 
Hmm, I guess for large volumes, eliminating lost blades due to warpage offsets any extra cost in abrasives-and for handmades, being able to straighten a knife while heat treating is worth saving money on belts, at least for some?

When grinding on the hacksaw blades, with a 4" angle grinder, I goofed and got the blade tip to turn blue and gold a couple of times, and even moving quickly on the flats I had dark brown spots where it took me just a fraction of a second to change direction while grinding. Kinda surprised me for high speed steel, the difference in lesser heat buildup using a 2X72 belt must be extreme.

Appreciate the comments :thumbup:
 
Almost all commercial knife blades sold by the major companies are ground after heat treating. They punch out ( fine blank) or cut out the blank, drill, profile, then harden and temper. Then they go onto the grinders. The are wet ground with grinding wheels, not belts, completely flooded with coolant while grinding. They lock the blade into a fixture and each side of the blade gets one pass, it only takes a few seconds. The blades are then surface finished, with scotch brite wheels, vapor blasting, media blasting or abrasive media tumbling.

I have watched this process at Gerber, and in the old Schrade factory in New York.

Bill Cunningham
Atlanta
 
hardheart said:
Hmm, I guess for large volumes, eliminating lost blades due to warpage offsets any extra cost in abrasives-and for handmades, being able to straighten a knife while heat treating is worth saving money on belts, at least for some?

When grinding on the hacksaw blades, with a 4" angle grinder, I goofed and got the blade tip to turn blue and gold a couple of times, and even moving quickly on the flats I had dark brown spots where it took me just a fraction of a second to change direction while grinding. Kinda surprised me for high speed steel, the difference in lesser heat buildup using a 2X72 belt must be extreme.

Appreciate the comments :thumbup:
Click to expand...

If your cutting something hard with the proper abrasive, it's not that big of a deal hard or soft.
You can wreck HT with a 2x72 machine with top-quality belts if you'e not careful as well. I use a mister or sometimes a cold-air gun and keep a close eye on things while doing it. If you're grinding freehand, you just have to make lots of trips to the dunk tank.
 
I grind all my blades and springs after heat treat, also maybe inefficiently, surface grind to specific thickness often after heat treat.
I am not too scientific about grinding to excessive heat but grind holding the balde in my fingers/hands and and keep a dip can real close to the grinder....
So far, steel is much below hardness change before the nerves in the fingers tell me it is NOW dipping time. And yes, there is probably a smarter way to do it, but most all of my blades are small compared to the makers who do those big beautiful straight knives.....and I do use only variable speed grinders and seldom run them real fast at all....
 
I think I read that a maker Loveless liked wet ground all his blades after HT. I dont know how anyone grinds a significant size blade ,>4" or so, having to dip it every few passes. I've tried it and every time I take the blade away and put it back, there's another facet that has to be fixed. I suppose practice has a great deal to do with it.
 
me2,

I wonder if you've noticed a difference in the past 6 years? :) This same problem has been giving me some trouble. My 4 x 36 grinder is a beast and gets my blades way too hot. When I get close to final thickness, I can't grind for more than a second without needing to dunk. Hard to keep an even, flat grind this way. Is the problem just that I need a lower speed grinder? I'm considering getting a rotating water stone/sharpening machine with a low grit for final grinding after heat treat...
 
Of course being able to slow down your grinder will help do the job. As well, if you are over using the belts you are going to heat your blade very quickly. Are you using the right grit or using too fine a grit and skipping one or more sizes? Hope this helps. Frank
 
I grind my blades after HT starting with a 60 grit cubitron and then go to a new 220 ceramic and on down the line. Dunking the blade after every couple passes I have very little heat buildup. I do run the grinder very slow though. Most all my blades are for folders and seldom over 4".
 
Here's a little trick if you like a convex edge: work just above the platen, it seems to carry excess heat away from the blade a lot better than working on the platen or wheel.
A sharp belt heats up way less than a worn one, too.
 
Another advantage of good belts is that they cut more even and do a far better job. You may find most of your problem is just over use of belts by7 trying to do a job they can't. Frank
 
Thanks for the advice, everybody. I start with a 50# aluminum oxide belt, but am definitely guilty of pushing them too long.
 
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