Hey how does everyone go about making knives from hardened steel? For example a wrench or a saw blade. Is it hard to keep it cool enough that you don't lose the hardness or should I grind to my hearts content and then normalize and heat treat? I don't have my forged burners built yet so I'd rather keep it hard. Also when you grind and get that blue colour is that the area that lost hardness or will the area around it be soft even if it doesn't change colour?
Hi Steve-O I am not sure how everyone else does it but I work hardened steel with the following in mind: Frequent cooling Light pressure Good fresh belts Fast belt speed Many passes I grind all my bevels after heat treatment. I have the ubiquitous water (or ice) bucket next to the grinder. Every pass or two I will dunk the steel. Old, worn belts will burn steel faster than anything. If you can imaging the tempering colour scale where that straw or light tan colour is ideal and a bluish-purple colour is spring steel. If you get a blue spot it means that area has essentially become spring steel. The thinner the steel the easier it is to burn, so pull back on the pressure when getting close to the point. Dunk and repeat. In general it's about your control of the pressure. Don't try to grind your bevels in four passes. I know it looks cools to see a stream of sparks shooting at your boots, but it really helps to take off a little each time. I don't slow the belt down, slowing the belt down affects the performance of the abrasives. I may take a hundred or more light passes to get the bevels done in a chef's knife. Dan
Dan knows what he's talking about. I will add though, you can't keep the steel cool enough. I've ruined a lot of steel by getting lazing with the water bucket. Mostly in the winter when I didn't want to get my hands any colder (i really need to heat my shop). I'm also terrible for overusing belts. DON"T DO IT!! Once the belt is worn, toss it. I know they're expensive but it's the cost of doin' business I'm afraid. You'll be amazed at just how much better things seem after getting that one thing down cold. (listen to Mr. 1 knife every other month here)
I'm going to take the opposite view. You can grind hardened steel if you're really careful but it's a lot more work and you will go through belts faster. In my opinion, the trade-off isn't worth it. Wait until you can anneal the steel, or set up a temporary heating area with some firebricks (or even your forge body, if you've got it ready) and use a torch to heat the metal.
Yeah if Dan does more then a hundred passes with a cool down after every one or 2 just to get the bevels in I was thinking that it would take me till my 103rd birthday to get a wrench down to a usable thickness. Might be worth the effort with a saw blade because it's already so thin. Annealing isn't a problem. I have access to oxy acetylene torches at work and can do that no problem. My issue is the rehardening. I have tried 3 times to harden with a 2 brick forge and have had mixed results. One cracked, one was overheated at the tip and one wouldn't get hard no matter how many quenches I tried. I have just been bitten by the knife making bug and I was hoping to find a way to get one done as I collect the parts for my burners. Thanks for the input.
If you are using a simple known carbon steel like 1084 (or even O1 in a pinch) you can harden with your torch. Again, a small cave of piled firebricks helps, but isn't vital. Just play the torch back and forth along the blade until you reach a nice even cherry red / non-magnetic and quench. That's what I did when starting out and had good results. O1 prefers a good soak but you can still get a decent blade using that method. The problem comes when you use unknown steels, like your wrench or saw blade. Any alloys in there are going to play havoc with the heat treat. Unfortunately, you really can't know what is in those without testing them.
Yeah the ones I have tried were all 01. Everyone's suggesting 1084 as a starter metal so I'll probably get some of that soon and try my hand at that. Still learning lots about grinding and stuff even if iam not ending up with hardened blades so at least it's not a compleat loss
When you say "you grind all your bevels post heat treat", you mean you take off a good chunk of the steel first right? I've recently been persuaded by my buddy to grind post heat too but i assumed he meant "grind a lot of the bevel first" and then grind the remainder after heat treatment. Just curious... for me the benefit seems to be that it's harder to make a huge slip after heat treating. It takes longer to get results but i'm less susceptible to slips. It let's me "figure out" where to remove stock first before i lose too much in the attempt. Can i ask (as somebody who likely has a better reason than it's harder to mess it up) why you do it this way?
Haha I like the way you think Todd. I always end up with ugly spots going up to the ricasso where the edge of the belt hits unevenly.
After almost 3 years of this, I'd still say I struggle with the plunge lines. I "can" free hand but it's still all over the place so I still use a jig. But even with that, it's very hard to get the two lines looking the same. It doesn't help that I made my grinder and it has some character flaws. When you flip the knife and grind the other side, for example, i have to check the tool rest for square first. I discovered that the rest isn't level... well, it's level, just not in relation to the levelness of the platen... It's confusing but it takes some figuring out. This is why i wanted to build the sayber (new contact wheels are in the mail !!) Anyway, my point it, I'm still working on consistent plunge lines after 3 years. I think grinding post heat treat may actually help.
Grinding the bevels after heat-treating can help reduce warping too, especially with a long, thin blade. I still prefer to do all the bevels first. Maybe just out of habit, but also because I still like using files. I stick to carbon steel and run a normalizing cycle before hardening to remove stress. I can't say I've every had a problem with warping.
There's sort of two main approaches: do the bulk of your bevel grinding before hardening, or do all of your bevel bevel grinding after hardening. I cut/grind out the profile, drill any necessary holes, then harden. I typically use 3/32" stock in longer blades, say 7 to 8". Keeping all of the mass there for hardening and reducing the risk of warping, which is one of the reasons I grind post heat treat. I use good ceramic belts that will tear through hardened steel without issue. If you think about it, you'll still be grinding hardened steel whether you do most of the grinding before hardening or grind it all treat after heat treat. If you are using a belt grinder the risk of killing the temper is still there. You could use files/stones/sandpaper to finish your bevels, but at hardness Rockwell C (HRC) 60 a blade is almost as hard as a file. I too would be 103 years old if I did that way. If you have some unknown hardened steel like a saw blade, you'd be better off to anneal it, machine it, and then harden it to your specs. There's no guarantee that the heat treatment of the saw blade is optimum for your purpose. Maybe the manufacturer of the saw blade wanted a bit mores springiness and tempered it to HRC50, in which case you certainly want it to be harder. You can take small pieces "coupons" of the same steel and practice a few recipes before committing. As also mentioned, wrenches on the other hand will likely have chromium, vanadium or other alloying elements in them which means you are trying to heat treat stainless steel which requires more precise temperature control than a DIY forge. Annealing stainless steel can be a very long process and likely not worth your time and effort. That's a whole other can of worms. Dan
It makes so much sense now. I'm going to try grinding it all post HT. I need to get some newer belts though. I tend to ...ahem... stretch the life expectancy of my belts beyond what i should. I know, i know... bad idea... Thanks Dan. Great info.
