Had a knife form a nice banana shape( slight exaggeration) in the quench. Tried clamping to a piece of angle iron for the temper cycle ( both cycles actually) and it's just as warped. Any tips, or is this another one to hang on the wall of shame? Cheers, Toby
Did you clamp it straight or overcorrect? I find I often have to overcorrect by about half the bend to end up straight if it’s a particularly bad warp.
Toby, No guarantees, but this one way that I have straighten blades. You'll need two small all steel C clamps, no plastic parts on them. Look down the blade and mark the place where you want the straightening to take place. Mark it with a Sharpie. Using a rod (big nail, hinge pin etc.) as a fulcrum and an old file or piece of angle iron, clamp the blade with the fulcrum at the point where you marked. See image below. Plan to make the opposing bent about two times more than is required to bring it straight. Set the tempering oven to a just under the original tempering temperature. Put the knife/jig into the tempering oven. Bake for two hours. Let cool, disassemble and check the blade. If required...repeat. If you can get it to the point where you can grind out any small curve/warp you should be good. Let us know how it goes. Dan
Ok Dan - thats a very detailed and appreciated explaination. I'll do it and let you know how it turns out. Cheers, Toby
Hi Dan - I'm sorry to report that after following your procedure the warp remains unchanged. I'm thinking of annealing now and starting over. Thanks again!
Thin sections can warp when they are not symmetrical and the thinner the more a small difference can cause problems.
So I've brought the knife up to just under tempering temperatures three times now well under clamps, to no avail. Would you gurus recommend annealing it and Heat Treating all over again?
I won’t speak to whether or not you should anneal it now (I’d be interested what the guys say about that myself) but I would say that it may be very likely that you didn’t over correct the curve enough. I have very limited experience with doing this with o1 but this method worked for me after a few tries but each time I over corrected more until it worked.
I would normalize the blade, straighten and check profile for uneven grind. Then go through the hardening steps
Well guys, I annealed, straightened and re hardend and it stayed nice and true this time. Thanks for all your help!
I’d like to ask something on this thread since we are on the subject. I’ll use O1 as an example, but this applies to all steel via the manufacturers recommendations. 01 from Hudson is recommended to be soaked for 30 minutes per 1” (25.4mm) of thickness. I have never had 01 warp on me when 3/16th’s or 1/4”...but did warp at 1/8th. So what if you pre-ground a 3/32 01 fillet knife or whatever, and then sandwiched that between two pieces of 3/16ths 01 and then soaked it for the recommended time for the overall thickness and quenched? Less likely to warp? Or would you still be concerned that the thinner cross section of the bevel (the cutting edge) not making contact in the clamping might still warp?
I think it would improve the chances of coming out straight. You'd be quenching a pretty thick "piece" at just under 1/2" thick when added up. Whatever fasteners used would be considered disposable unless you use some kind of high temperature anti-seize compound on the threads. I've used bolts to squeeze layers when making mokume gane and I had to cut the bolts off. Usually one would leave some additional steel, say 0.050" on the edge when hardening. If the spine comes out straight, you'll have a little wiggle room to grind the cutting edge side into a straight line. It would be best if you grind the bevels after heat treatment and have all three parts of the sandwich in full contact with each other when hardening. No matter how you slice it, hardening steel of varying thickness means different rates of cooling in the same piece of steel. Dan
Anything that uses threads for clamping will weld itself together once welding temperature is reached. When the steel is in the furnace I would not be concerned with warping. Warping occurs from asymmetrical profile about the vertical section or is bumpy or uneven. Once the martensite temperature is reached all hell breaks loose internally and steel volume changes.
100% talking about bolts that would be cut away after quenching. Use two straight pieces of 1/8th or 5/32 to knock down the overall thickness. Again though, regardless of thickness, steel is still austentized at the manufacturers recommended temp and time, and it’s still quenched in the recommended media be it oil, air etc. Never have I seen in tech sheets that you have to change your method of quenching depending on the thickness of steel. For example tech sheet’s don’t say for 1/16 - 1/4” quench in Parks AAA...and anything above that quench in Parks 50. I think if anything it would be down to ‘volume,’ of oil in oil quench scenarios. You would not quench a 1” x 2” x 8” bar in a bread pan lol...you probably dunk it in a full 5 gallon pail. And air maybe still air vs forced air? Anyway, food for thought, it’s just me trying to get out of post HT bevel grinding (hate the thought) haha!
I think a subcritical anneal to relieve any stress would probably work better than sandwiching. The issue I see with sandwiching it would be that you have a small gap between the layers. This will prevent the oil from properly contacting and circulating around the blade. What you effectively end up with is hot oil trapped between the layers, cool oil not getting fully to the knife, and the oil just cooling the outside layers as they pull the heat from the inside layer. Basically it’s going to create the worlds slowest plate quench. Oil quenching sandwiched layers with air gap can also cause the small amount of oil that gets between plates to flash boil and shoot out.
