Introduction: Making a Pattern Welded Pruning Knife
In this instructable I will show you a step-by-step process I used to create a pruning knife.
But first, what is a pruning knife?
A pruning knife has a curved blade similar to a bill hook, which is used to cut vines, harvest fruits or vegetables. It usually comes in a folding variant that is hand to store in your pocket. Most blades also have a spring that assists in opening, closing and keeping the blade locked when in use. There are also different variants with different blade shapes but I won't get in to that here.
For the blade I used:
-20x20mm bar of wrought iron
-an old file
For the handle:
-a piece of yew
-two 3 mm thick brass pins
-initially I used a coil spring but later I switched to c45/1045.
Step 1: Forging the Blade and Spring
As stated in the title I forge welded the blade from three pieces. The wrought iron serves as a base, then a file is inserted in the middle which serves as a cutting edge. In reality the blade would be much better off if it was made from just one material, rather than it being out of multiple pieces. When forge welding there is always a possibility that there will be an inclusion or a delamination that can ruin a blade. But forge welding is fun, challenging and the outcome is always pretty.
First comes the splitting of the bar of wrought iron in to two pieces. That is done with a hot cut tool and a striker. This step is visible in the second picture. The split came out very ugly and needed a lot of cleaning up on the grinder. That is because of the wrought iron, it splits very easily and starts to fall apart. But it didn't cause me any serious problems.
While the piece is cooling down, I start working on the edge material. I chose a smaller old file for the job. The file is first heated up so it looses its hardness, then I ground off the teeth. It is then inserted between the two layers of wrought iron and closed tightly.
The billet is heated up and sprinkled with borax for easier forge welding. It is heated until very bright yellow and quickly taken to the anvil where I hit it lightly with my hammer. This process is repeated three times to ensure a good weld. After the final welding pass I can start to forge out the blade.
When forging the blade I didn't forge completely to shape and thickness, because that could move the cutting material to the side. Basically I just forged it into flat stock and then cut out the blade shape.
And now for the spring.
I designed the spring myself, that way it fits best with the blade shape and handle. Initially I used a piece made of coil spring and used that until I had to assemble the blade together. And then just at the last moment I broke it. I then discarded the idea of using coil springs further and went with c45/1045. 1045 is a construction steel with a medium carbon content. It is water hardening and takes a lot of abuse before it finally starts bending of cracking. I had a 20 mm round bar lying around and forged it into a small piece onto which I drew my design and cut it to shape.
And that concludes the forging part of this build, the next step is
Step 2: Grinding the Blade, Hardening and Polishing.
With the blade and spring ground to shape the next step is grinding the bevels.
This is a pretty straight forward job and there isn't much to say. I ground them on a belt grinder using 40 grit belts, when done I polished it with a 100 grit belt.
Before this process a 3 mm hole was drilled in the base of the blade and the spring. And I also filed a notch on the back on the blade where the spring locks the blade in place.
Then comes the interesting part - the hardening.
This process is done at the forge. The blade is heated up to a hardening temperature and it is left to cool down. This is called normalization and is repeated three times. This enables the steel structure to repair itself and relaxes a little. After that, the blade is heated up for the last time and quenched into sunflower oil. I checked it with a file and the hardening was a success. The same process is repeated with the spring, except that it's quenched into water.
Right after the hardening the blade is tempered. This is also done in the forge. The blade is held above the embers and slowly heated to a golden color or about 220-250 C. The same process is used for the spring except the temperature used is higher 300-350 C.
The blade is almost done it only needs polishing and etching. All the blade surfaces are polished with 100, 320, and 1000 grit belts. After that it's continued by hand using 120, 180, 240, 360 grit sand paper and finished with scotch bite pads and steel wool.
And now its etching time.
I used ferric chloride for the main etch and continued with instant coffee. The blade and spring are submerged into the acid for a couple of hours. This really brings out the grain of the wrought iron which came out really great. One side shoved a nice line between the iron and steel. The other side not so much but its still usable because of the carbon migration that occurred between heating. Then I mixed up a glass of instant coffee and left the pieces inside for 2 hours and polished the pieces with steel wool. The end result is visible in the attached pictures.
Step 3: Handle Making and Assembly
The last piece I still need to make is a handle with two slots. One for the blade and one for the spring. Making this handle was probably the hardest part of this build.
I started out with a piece of yew roughly the final size. On to it, I drew the handle design and pin locations. I drilled a 3 mm hole for the blade to rotate around the handle. I then marked the position of the closed blade and started sawing out the recess. The saw was used as much as possible, then I continued to remove material with a chisel that you can see in one of the attached pictures. This took almost and hour of fiddling with the chisel and small files but the fit was perfect. The same process was used for the spring slot and a little help from a drill.
With this done I shaped the handle to its final size and drilled the spring hole. All the edges were rounded and polished. I inserted the knife blade and spring and cut two brass pins slightly longer than needed. They were inserted into the holes along with the blade and spring and penned with a light hammer. The ends of the pins were filed smooth and sanded. The only thing to do now is to oil the wood and sharpen the blade.
And with that the build is concluded.
Step 4: Conclusion
This was a nice and fun build. It challenged me both in spring making and forge welding. The locking mechanism works smoothly and holds the blade firmly. And the beautiful yew wood gives a really nice contrast to the complex blade surface pattern.
I hope you enjoyed reading this and that it may inspire you to try something similar.
Best of luck,
Participated in the
Build a Tool Contest