Here's how I used my LEAD CNC 1010 to make a practice butterfly knife out of aluminum and some scrap wood from my shop. This is for anyone who might like to casually play around with a butterfly knife without the whole cutting your fingers up part.
- Machine Type:
- CNC Router
- Adobe Illustrator, OpenBuilds CAM, OpenBuilds Control
- Machine Time:
- 1.5 hours
- Bit or Laser Size:
- 16th" 2-flute fishtail/upcut
- Feeds & Speeds:
- Aluminum: 10 in/min, depth .002"
Wood: 40 in/min, depth .03"
- 6061 aluminum, canary wood, maple
Here are the parts I scrounged up for the project. I grabbed some 1/4" and 1/8" thick aluminum, some scrap 1/4" maple and canary wood pieces, a few stainless machine screws, and a couple brass standoffs and nuts. I knew that this hardware wasn't exactly ideal, but it's what I had on hand and I still wanted to give it a shot and see if I could make something passable with it.
Knowing what I had to work with, I began designing the parts that will make up the practice knife. This was pretty quick work, with most of the focus being placed on the blade design. The most important thing was making sure that the blade would fit comfortably inside the handle channels and that the handles and blade would align correctly both when open and closed.
Next I glued up and clamped up the two pieces of wood together. While that was drying, I got started on the "blade" (Is it a blade if it's never going to have an edge?).
To get set up to cut the blade, I attached a 1/16th" upcut bit to my spindle and secured the work piece down with a couple of clamps I made out of scrap plywood. I didn't put much thought into making these clamps, but I'm actually going to hold on to them since they worked so well. I'm always a little paranoid with aluminum since these tiny carbide bits break so easily.
I've got my CNC system in an enclosure I built to cut down on noise and dust. It works pretty awesomely and my ears and respiratory system have been thanking me since making it. Yes, that is a bathroom grab bar for the handle - works a treat.
From the enclosure windows, I can keep an eye on how the job is going. Getting clean edges and keeping the bit from getting too hot requires low speeds and cut depths, especially since I'm doing this dry.
I spaced out and also carved the latch out of this thinner 1/8" piece of aluminum instead of the 1/4" sheet, but no big loss there, I just discarded that part. Otherwise, everything looked great.
After I cut the 4 small tabs holding the "blade" in place, I could begin cleaning it up. No big job here, as the cuts had come out very clean.
10 minutes later, I had a pretty nice looking piece - this came out even better than I had hoped for. You'll notice these holes are way too small to do anything with, this was on purpose but I was probably being a little lazy. Knowing I would be tapping the lower hole to receive the threaded standoff, I figured I would just drill the holes with the exact drill bit size that I know my tap likes. This saved me measuring the bit and potentially having that hole size be a little bit off.
I need to get a better clamping situation going on with my drill press, but this worked well to get me the exact holes I need. Having the centers of the holes marked by the CNC router makes this pretty foolproof.
A few twists of the tap and the hole is threaded and ready for the standoff.
I wanted this hole to be threaded so that this part could not spin inside the hole. Here it is not yet correctly aligned; flat sides will be pointing left and right once it's installed later. A little thread locker will be added to make sure it will really stay put.
The latch was carved from the thicker 1/4" sheet of aluminum, which the LEAD CNC had no problem with either. Since this was my first time cutting aluminum on this machine and because I ran it dry I was pretty conservative with my speed, but I'll be running future jobs faster and faster to find my ideal settings.
Because I didn't have much excess surface to clamp down on to, I decided to use double-sided tape for this part. This can be a little nerve-wracking as it is not as secure as clamps, but this was going to be a quick job so I just stood by to keep a close eye and make sure there was no movement. I also like to periodically press down gently on the work piece to make sure the tape isn't lifting off the wasteboard during the carve because I'm a worrier.
I made a big rookie mistake here, but had to just let the job finish at that point. This glued-up piece was 1/2" thick, but my bit begins to taper around 3/8" up. That's why these top edges look so ragged here, that part of the bit is not meant to do any cutting and so was just tearing up those edges. It left indents where the bit raised to leave the tabs below, which was another thing to fix.
You can see the result better here, it didn't look great. But it was nothing that couldn't be remedied with some quick work.
To fix the ugly edges, I used an edge trimming bit with a bit of taper to it. I was able to adjust the bit to a height where the angle of the blades aligned pretty perfectly with that tapered edge. This cleaned off all that ragged wood that the bit ate up along with the phantom tabs. Happily, the resulting taper was not very noticeable and almost looked intentional. Score.
I had to file out all of the corners in the handles so everything would fit snug. Using a small bit in the router helps make this pretty quick work.
After a little elbow grease the handles were looking promising. Good, even.
At this point, I could start mocking up how everything was going to go together. My design calls for the of the handles to be tapered slightly so that the blade doesn't look too thin where it meets the handles. So I next had to reduce the width of each handle by about 2mm near the top with some sanding blocks and elbow grease.
You can see the slight taper here. It isn't huge, but it will be noticeable once the blade is attached. It was important to have this just right so that the arc of the handles would be correct later.
Home stretch. I drilled holes in the top of the handles, supporting the overhanging pieces with the aluminum latch to make sure they didn't flex much. These holes need to be straight so they don't bind with the screw that's going to be going through it.
With the holes ready, i could test the fitment and mark where the standoff that acts as a tang pin will meet the handles. This contact area needed to be filed down so that the handles could fully close and hold the blade tightly.
Now that I was confident that everything was going to line up correctly, I could install the makeshift tang pin with some high strength threadlocker.
Since I was just using regular bolts and nuts for the pivot pins, I had to recess the hole opening to hold the nuts and keep the backside looking nice. If I make an improved version of this, I'll buy some more appropriate hardware that will look and function a little better.
With that drilling done, I realized I had made a second mistake. I filed down the wrong sides of the handles - the insides will not be coming in contact with the tang pin. Some blades do actually have a second pin higher up that would hit the insides, but my design did not include one. I went ahead and filed the correct side as well and it actually didn't look too bad, so no huge loss.
Finally the last piece. All I had to do to complete the latch was first drill a hole in it, starting with a tiny bit and then moving up to my final size...
...and then round off the two edges on that side. I started shaping them on a grinding wheel and then moved to a sanding block.
The last piece was ready and I could finally assemble everything.
And here are the final parts laid out for assembly. I realized I needed something like plastic washers between the blade and handles to make everything move smoothly. All I had on hand were some brass washers, so I went ahead and used those. I imagine they'll create a lot more friction than plastic would, but this seems to be an okay solution for now.
I'm happy with how it came out despite the small mistakes I made. After playing around with it, the only major issue is that it does not weigh quite enough. And because of its crazy light weight, it's a lot more difficult to control than it could be. Still, it actually moves really smoothly and feels good in the hand, enough so that I feel good calling this one a success. I might revisit this design to add an oz or two of weight, which I think would improve it significantly. Thanks for checking my project out!