One Piece Carabiner From Scrap!

Back in 2019 I was working on making a slipjoint knife entirely on my homebrew cnc, bevels and all. I ended up making an instructable for that project which can be found here The-Slipjoint but shortly after that was written, I ended up packing up my workshop, selling off my cnc as well as a few other nice big toys, and moved into a new house. Since I didn't have a way to make more of those little slipjoints, the stock i had cut was just sitting dormant in a drawer for years. When I saw that there was a scrap challenge here on instructables I thought it would be neat to make a compliant mechanism version of a carabiner and that scrap would be absolutely perfect for the task.

Very important thing to note! This is not a climbing carabiner! This is not meant to support your entire weight, it may be steel, it may be sturdy, but the latch has no way of locking which could result in serious harm or death if used incorrectly.

heat treatable steel or titanium

jewlers saw with #6 blades

handfiles

a drill

a clamp or vice

a way to heat treat your steel

tons of elbow grease

I ended up taking the measurements of the steel I had on hand and made a cad model of the carabiner I wanted to make. The long thin cutout there will act as a spring, and the little zig-zag pattern will also aid in providing more flex to the mechanism (not as much as I would have wanted though)

Anywho, this picture should be scaled to be printed on a standard 8.5x11 sheet of paper (A4?)

If you want to, feel free to print it out and give it a go!

Before spending hours and hours on this project I wanted to at least test out the design and make sure it would work in the first place both in terms of scale and function. I had some spare acrylic laying around so I printed out a sheet of the designs and used some spray adhesive to glue the paper onto the acrylic.

Using a jewlers saw I went through and cut out one profile. In doing so I found that all the sizing was spot on! More importantly though I found that the order in which you make your cuts makes a big difference on how easy or hard it was to work on!

To begin, I used another printout of the design and spray glued it onto the little piece of 440c. Just to make sure the printout was on there really well, I rubbed the paper down with a 2x4 cutoff.

I then took another offcut piece of wood and made a little jewlers v-block. This allows you to support your workpiece a lot better while cutting with a jewlers saw. I think the logic behind holding the part down with your hands instead of just clamping it is that since your part can move more freely, the blade will bind less which means that your blades will last longer. Just a guess though!

The first cut I took was that long spring cutout. If this was done later down the line, the sawing would cause the part to get real wobbly and it would generally make your life more miserable than necessary.

Next up, drill a small hole on the interior of the design and fish the jewlers saw through there. Even though we could come in from the side, I highly recommend doing it this way, since again, you want to maintain as much rigidity per cut as possible.

This whole project will teach you a lot about sawing, make sure you only cut on the downstroke, take your time, apply just enough force but not too much. Every broken blade is a new lesson I learned, and by golly i broke a lot of blades.

Back to the cutting process, after you cut out the core, I nipped off the short end of the material first and then went for the longer exterior side. I'm not sure if the order really matters here or not, but it felt right to me.

Ooooof, that was a lot of sawing, it's not done yet, but if you made it this far, the worst is pretty much over!

We are about to move into the sanding phase of the project, which means we will be loosing the paper template that has been guiding us this far. Just to make sure you know where to place that final cut, just make a shallow cut across that opening line.

Now it's time to hide all those little imperfections from the sawing process. Clamp down your part to make your life a little easier and start working on all the parts that you can reach. Looking to get nice, smooth, flat, and continuous surfaces. The more careful you are in this step, the better the end result will be!

Since its going to be a pain to chamfer the exterior round surface, I took a c clamp and a spare piece of material to securely hold down the part while filing. Make sure to have contact on both sides of the oval as it will prevent the part from moving on you while you take passes with a file.

Steel often comes with mill scale on the surface, it can be nice to look at if you are intentional with it, but I really wanted to keep everything nice and clean. I started by removing the mill scale layer with a file. After I removed all the little bumps and stuff from that face I started sanding the metal in one direction, trying to keep all of the scratches as uniform as possible. This just makes stuff feel way more proffessional. I should note that when i say one direction, I mean just move forward with the piece, lift it off the sandpaper, then repeat. If you go back and forth you will get a little pattern of "j hooks" which make the surface look a little sloppy. That said, this is not exactly the neatest work I have done, but its good enough for a keychain.

After all the sanding was done, I felt like it would be a great time to make that final cut, but I should have done the little zig zag cuts first. Live and learn!

Now just get back in there with a jewlers saw and cut out the little zig zags. Once cut, you will need to come back in and knock down the sharp corners at the entrances to the the cuts. Future me would tell past me to make the cuts for this part wider, since they didn"t flex as much as I was hoping for.

Ok now we switch gears over to heat treating! Before we do anything, make sure to put on some gloves and degrease the part! You could just use soap and water, but I opted for acetone.

Since this is a stainless part, we are going to wrap it in stainless steel foil wrap in order to prevent oxidation of the steel. If we used aluminum foil instead, the foil would just melt due to the high heat involved.

If you have not worked with stainless foil before, its pretty similar to aluminum foil, but its stiffer and will cut you pretty quickly if you are not careful. Every time I cut off a piece with tin snips, the cut edge ends up being really nice and jagged which lends itself great to cutting your fingers. Use leather gloves if possible here

In order to get a nice happy seal we are going to fold over the edges of the foil twice. On the first fold, make it fairly large since we will need to fold that area over itself. Once folded, crease the edge with some scrap wood and use the wood like a little hammer if the foil is being uncooperative.

I reference this post every time I do heat treating of 440c and always get great results from it! If you ever hop onto bladeforums.com Stacy is one of those members who I place a ton of trust in.

I placed the foil packet into my heat treating oven before I turned it on. I can never remember if this is good to do or not but it prevents me from getting all stressed out about the perfect time to plop it in the oven.

440c requires plate or air quenching, so as soon as the heat treatment is done, I'll pull the material out, place it on top of a big aluminum block. Without cutting the bag open, ill take a second aluminum plate and place it on top, making a very toasty sandwich. Sometimes I'll clamp the two plates together, but i find its faster to just sit on the sandwich instead.

After a minute or two the little baggie should be cool to the touch which means you can go ahead and cut it open. Also I always find it super cool that aluminum can just suck the heat right out of a bright orange piece of steel so fast!

So a couple steps ago I showed a heat treating recipe. That recipe is awesome but I didn't have liquid nitrogen on hand to do a deep freeze, and also we actually want this steel to be a lot softer than what a temper at 375 would provide. Generally speaking, during the tempering process you would want to get the steel as soft as possible if you were going to use it as a spring, but since my regular oven only goes to 500f, that's what we are going to have to settle on.

I know i could just use my kiln again, however you need to get the steel tempered as soon as possible after quenching in order to prevent if from just randomly cracking on you from all the internal stresses that have just built up. If I was going to use my kiln, I would need to drop the internal temp of the kiln from about 1900f to 1100f in a very short time span. Maybe I'm totally wrong, but I feel like that would end up damaging my kiln.

(heat treating chart from alphaknifesupply.com and can be found at the bottom of this linkylink)

After heat treating if you are at all like me you will want to play with opening the little mechanism. Also if you are like me, you may find that its just a touch tougher to open than you would want, and that's totally ok, and fixable! All you need to do is just thin out that little spring area either with sand paper or a little grinding bit from a dremmel. Just remove a bit of material, check the force, remove a bit more, check again, and repeat until it works for you! Take your time with this step since you don't want to end up with a floppy spring.

That's it! You are done! You did it! Congrats!

Some closing thoughts though, first off, there is a bit of a pinch point at the bottom of the lever section, if i was to do this again, I'd probably just cut out that area or add a bigger bevel there.

Very important thing to note! This is not a climbing carabiner! This is not meant to support your entire weight, it may be steel, it may be sturdy, but the latch has no way of locking which could result in serious harm or death if used incorrectly.

All that said, this was a really fun little project and I'll be entering it into the scraps challenge! I hope I get your vote! Outside of that, i really hope some other folks try and make one of these!

Hope you have a fantastic day!