The Sickle

Not too long ago I moved into a new house, its got a small yard and that introduced me to a problem I've not really encountered before, yard maintenance. At first I thought oh, no problem, just get a weed whacker and call it a day. However there were some issues with the weed whacker, first my girlfriend and I both wanted to grow various plants in the yard and the weed wacker was not precise enough to avoid all of our baby plants. The second issue was that while cutting stuff went quick, since the whacker kept recutting grass the cleanup process became more time consuming and labor intensive than necessary. Even if we used a lawn mower it still wouldn't solve these issues so we started to do some research on alternative options.

After a bit of looking, I ended up finding this 20 or 30 dollar sickle off amazon. It was a blast to use however it got dull after about 5 or 10 mins of cutting, plus the tip kept excitedly discovering various rocks in our yard which cause it chip a number of times. It worked well enough, and was absolutely worth the money I spent on it, but I knew I could make a better version.

Curious about how the cutting action of the sickle worked, i ended up taking some slow-mo footage in order to see what was happening to the grass as it made contact with the blade. I found that as I was trying to cut things I was naturally aiming in a straight line out from the axis of my hand (see the photo with the red dots). The grass would clump in that area and not get cut very effectively. To solve for this, I just traced the proportions of the sickle and extended the blade back so that red dot would be at the middle of the blade instead of the end.

I made a quick card stock mock up and experimented with some grass. Even though it was only paper, it was clear that there was something to this idea.

Using fusion 360 I ended up tracing out a jpg of the sickle and built up a basic 3d model. Then I made a quick laser cut plywood version. This one had a little angle gauge so I could more easily figure out exactly what angle worked best for cutting.

I wanted to keep this thing as light as possible, but it needed to be tough as well. As I was browsing around I came across Richlite which is made by taking a lot of layers of paper, laminating them together with a low formaldehyde phenolic resin. It's a pretty neat material and I found that this cutting board was the cheapest way to get some at 1/4" thickness. I was wondering just how robust this was so I cut off a narrow length of it and tried my hardest to break it. I couldn't even come close to breaking it with any normal amount of force! Anywho, it's a cool material, supposedly sustainably made. If you do use it, just make sure you wear a respirator as you work with it.

This is a super complex step, but you take the form you want to copy, and use a pencil to trace around the shape, this way you will know where to cut the material when its time to cut. Crazy right?

I ended up cutting out 3 of these center parts, this was before I did that flex test since I wasn't sure if i'd need to laminate them together for strength. I still ended up using them a lil later though

I just wanted to share this, because that pup was having a nice day in the sun

I ended up breaking the first laser cut blade shape, so I just traced the broken one onto some plywood and cut out a non-broken version

So the chinese sickle back in the beginning used some basic carbon steel for the blade, but it dulled too quick. So i thought, what the heck, why not go all out and use one of the most absurdly wear resistant steels out on the market, CPM10v. To my surprise it cut really really easily on the bandsaw, maybe it won't be too bad to grind!

With a file (and later a belt sander) I went in and cleaned up the profile of the blade before heat treating.

I ended up using 3 holes because I wanted to make sure that there would be plenty of shear strength in the head joint, that way if i hit something hard, the blade wouldn't just pop off.

Just found an angle of the blade that I liked, clamped the handle to the blade, and drilled through the handle using the blade holes as a guide. (this should probably be done on a drill press instead)

After all the holes were drilled in the handle, I added a second clamp to make sure everything was perfectly secure. I then popped over to the belt sander and made the back end of the blade flush with the handle.

I live over in northern california, we have a lot of wildfires, to prevent wildfires the park service here hires out goats in order to eat back all the dried out grass so there aren't great big fields of combustible grass. Thought it was worth sharing!

Before heat treating its a good idea to degrease your blades as any oils from your hands may be etched onto the blade at the high heat. Also, make sure the blade is totally dry before tossing it in the kiln.

Ok since we will be heating up this blade to a super high temp, we need to wrap it in stainless steel foil. This will prevent the blade from forming some nasty scale which is a pain in the butt to remove. Also i've seen some folks say that adding a bit of paper into the foil will help eat up any excess oxygen, so sometimes I like to write little notes or good wishes on paper and stick it in. I've chatted with a material scientist who thinks the impact of the paper eating up oxygen is negligible at best, but I still think its fun to do.

After waiting about 3 hours for my kiln to reach temp, I threw the blade into the oven at 1970f, just a few degrees below the target temp. This was just so that the kiln could restabilize its temp, and then initiate its timer once it reached 1975f.

If you want to see where I got this heat treating recipe, look no further than knife steel nerds!
https://knifesteelnerds.com/2020/08/03/cpm-10v-steel-history-properties-and-how-to-heat-treat/

Once that 30 min soak at 1975f is done, we need to cool down the blade quickly, but not too quick. The faster we try to cool this, the great the risk of warping or cracking. Cpm10v is air cooling which means you could literally just pull it out and let it cool in the air to quench it, but sticking it between 2 slabs of aluminum works a little better since it will force the steel to stay flat. I also left the steel at full thickness in order to prevent any additional warping.

As soon as I was able to touch the blade with my bare hand, I stuck it in liquid nitrogen. This will help make all the crystals in the steel turn into nice happy strong crystals.

Also its worth mentioning, don't grab steel with your hands while its in liquid nitrogen. I did, and i burnt my fingers a little, kinda similar to touching a hot pan in the oven...just...cold?

Once I pulled it out, I let it hang and come back to room temp in the air. The reason I wanted to hang it specifically was because if i sat it on a surface, one side may warm up faster than the other which could cause warping.

Alrighty, and in the oven it goes! Again, to prevent warping I wanted to have as much of the steel contacting air as possible, both during the heating and cooling.

To start grinding any blade I find its easiest to create an initial bevel. Just take your time and make sure everything looks even and symmetric.

I used a couple pieces of hardened steel as a guide for my bevels, just so that the plunge would stay nice and even.

For an inward curved blade like this one, I found that using the edge of the sanding belt yeilded great results for this phase

As the bevel reached the back of the spine I was able to use the full width of the belt instead of just an edge. Once the bevel got all the way to the spine I just kept feeling the edge of the blade to check for thickness. I do this by pinching behind the edge and then pulling my fingers away from the blade. Thinner is generally better, and a slight convex bevel is also good to use.

One thing to note about using cpm10v, it eats belts. I went through close to 10 coarse ceramic belts just grinding this, and it took a good 4 or 5 hours to do the entire grind. Also i should mention im using a 2x42 belt sander with 1/3hp, so a beefier sander may do better. Since I knew it would take a long while to grind before starting, I actually didn't hate the process at all. Instead i was just glad I ordered extra belts!

This was a weird experience. I ended up using a little diamond file that came with one of my leatherman multitools, and it just very easily added a little bevel onto the blade. With the amount of grinding belts I went through I was fully expecting that it would take a long time to add an edge, but it honestly took about the same amount of time as any other steel.

Just to add a little thickness to the handle, I ended up cutting out some handle scales from those extra handle cores I had cut earlier. If you ever end up making scales just make sure that you do the front end before you attach them to whatever you are working on. Once they are glued in place they become substantially harder to work on.

Pretty simple, just marked out where I wanted the scale pins to go, drilled some holes in the core, then used those holes in order to drill the handle scale holes. Also make sure you use a wood backing so the material does not explode out the back.

Just stick a brass rod through your scale holes and saw it off leaving a decent bit of excess material. This excess is just in case anything gets stuck while you are working on it you now have little handles to use

You could technically do this bit at the end, but with everything dry fit I ended up belt sanding the profile so everything was flush, then cleaned it all up with a file.

Next up lets nip off some pins for the head to blade joint, again making sure to leave a lil excess.

I know some people dont like using epoxy from bottles like this, but I find them way nicer than using the plunger style dispensers. Anywho, there was a little bit of rust on the blade so I just cleaned that off with a little scotchbrite pad, then slathered epoxy everywhere and added some clamps. It got pretty messy so i ended up using some paper towels to prevent the clamps from getting stuck. Since this tool is just for me, and since ill be using it for a lot of yard work, I could care less if there is a lil excess epoxy here or there.

After letting everything cure overnight I removed the clamps and found a fair bit of paper towel stuck to the richlite. Nothing a little elbow grease couldn't fix!

Ok now it's time to go through and trim off any pins that are proud of the surface. We want to cut as close as we can to the surface, but we also don't want the saw to start eating away at the non-pin material.

This is just about the end, but we just need to file down those pins so everything is flush, then start shaping the handle. As with any handle shaping we want to make sure there are no spots that feel like they are poking into your hand. So every couple of minutes actually feel the handle, squeeze it hard and see if it hurts anywhere. If it does then adjust.

Once everything feels nice and comfy, its time to clean up the surfaces. Just take some sand paper and remove any marks from previous grits. This process can change how surfaces feel so just be sure to keep checking to see if any new hot spots form.

If you really want to go wild, see if you can control where your facets are, have some that blend out and some that are super nice and crisp. It's incredibly challenging, but also fun and nerve wracking. I didn't go all out on this one since I mainly just wanted a nice looking tool that would be used to cut grass, not a show stopper. Maybe one day ill make a more sculpted one.

let me preface by saying, im not sure exactly if this is an ok wax to use on richlite, but it is my favorite wax to use for finishing things. Feed-n-wax is just awesome stuff that smells great!

I ended up hitting a few rocks and a log by accident which chipped the tip a bit (not at all suprised) So i will need to make some modifications to the design. That said, holy cow this thing is a beast. That pile is probably about 1 meter high and 1 meter in diameter of just grass, all cut without needing to be sharpened. By the end of that cutting session the edge needed a little touch up, which only took about 2 minutes before it was shaving sharp again. This thing is an insane improvement over the chinese one!

Thank you so much for reading this whole thing! I had a ton of fun working on this project and I'll be submitting it to the home and garden contest. If you liked it I hope i can get your vote in the contest!

Lastly, I'm really curious, would you use something like this? I'm in the process of building a cnc and will hopefully be able to make stuff like this on there so I can make and potentially sell them at a reasonable rate.

Anywho, I hope you are having a fantastic day, and if not, I hope things look b