The Cleaver: Part 2
Back in the shop and today was all about refining the shape, rough grinding and then the most nerve wracking process for a cutler; hardening!
Again, I am faced with the shadows of envy when I start writing a post. The envy being that my fellow artists here have the luxury of not only having a clean space for taking pictures (it is amazing how quickly the speakers on one’s phone collect metal dust and shavings in the shop), but that they can take pictures as things progress easily! In smithing one has about 15-30 seconds of workable heat (depending on the mass of material you are working with) once you take a piece out of a forge. Of that, only the 3/4 of that heat is useful for effectively forging out material. The rest is straightening and truing up material. Every heat takes time and also adds scale to the material and reduces the overall mass, so fewer heats is always best to maintain the cleanest end result.
But I digress. The end of all this wining and excuses is this: I will do what I can to get interesting ‘Work in Progress’ pictures, but there will be some inevitable gaps in process. Best thing is to get in touch and book a quick intro lesson to see it all for yourself (yes, yes…shameless plug. Totally ineffective given a global pandemic too!)
I try to forge as closely as possible to final shape given that I enjoy smithing and not so much grinding! Regardless, I am not proficient enough to eliminate the entire cleanup process with a grinder and above, you can see the layouts for the final blade shape. Further, the integral bolster was refined on the bottom roller of my Oregon Blade Maker 2″ x 72″ belt grinder. I lucked out that it was the right profile, but I think that the next thing on the ever evolving shopping list is going to be a set of small-diameter contact wheels. Getting into tight radius areas when shaping things like handle transitions and such is just so much nicer to do via power tools rather than files!
After rough shaping, it is all about the heat treatment. Heat treatment is the process where one takes the material to a specific temperature, then quenched in order to increase the hardness of the material. I’ll get into the specifics of all that in a later post (I find it fascinating, but I can imagine that it isn’t quite as interesting as glowing metal). First stage of heat treatment however is normalization: heating the material above the critical temperature, holding it there for a period of time, then cooling off in air. During heavy forging stresses develop within the crystal structure of the metal. This normalization process serves to normalize the entire structure and both reduce the likely of fractures and refines the grain structure (again, more on this later when I get into Shop Metallurgy).
So pretty isn’t it! After the normalization, more grinding! You can see that there was some additional material I needed to deal with at the tip to even out the thickness. Following normalization and any additional tweaks, it is time for the quench! Take a piece of hardenable steel (again, more on that later), bring it past the critical point and rapidly cool according to the material requirements. For most spring steel, this quench happens in warmed oil – I use canola – as it achieves the correct speed of cooling. Other steels will have different requirements and require either faster or slower quenches. Some steels also harden when cooled in still air (most stainless steels).
Know what you are using and apply the correct heat treatment process! This is one of the biggest dangers of Mystery Scrap Steels – you really don’t know what it is you are using. You can see if it is a mild, carbon or stainless steel, but the specifics are lost without a metallurgical analysis unavailable in a small shop.
And again, I digress…
After the quench, the material is exceptionally hard (if you did everything correct) and therefore brittle. To make this a useful tool, one needs to strike a balance between hard/brittle and soft/malleable. This process is tempering – bringing a material up to a significantly lower temperature to loose some of the hardness and bring in a level of malleability. For this material, a 400°F for two hours – repeated twice – brings down the hardness to a nice balance!
Yes, I used my kitchen oven. This process isn’t any different that seasoning a cast iron pan! I would like to draw your attention to the hammer marks on the blade for a moment. I always try to forge as clean and straight as possible, however the customer wanted a ‘brute du forge’ look for this blade to reduce material sticking to the blade when getting through large chunks of animal. As I had completely forgot about this and was exceptionally careful about forging as clean as possible, I then had to add back the marks. Ahh well, lets consider this a lesson in ‘Pay Attention to the Design Brief!’.
All in all, I think it is coming along very nicely! The next part will be all about finishing and adding a handle! To be honest, my least favorite part of the entire process…
