Introduction: How to Make a Stainless Steel Folding Knife in Two Days
After many attempts of making fixed and folding knives, I finally decided to do a little research and design a better folding knife than I'd been making. So I tried to use the most simplistic knife design I could. This is a frame lock knife, which is about the simplest, and most sturdy design I have found. So after creating a successful design I decided to share my steps on how to make it.
Step 1: Tools & Materials
Now you can make this knife with all hand tools or with power, but either way your going to need some way to make the bevel on the blade. You could use a file but that might take days, I suggest a belt sander or angle grinder, thats up to you.
This design is all stainless which I thought was great since it will never rust so no worries about using with water or anything.
So regardless of if your using power tools this is a list of all of the required tools as well as the extra power tools;
2. X-Acto Knife
5. Sandpaper in reducing grits from 60-400
6. Taping Head and 4-40 and 8-32 Taps
7. Hand drill or Drill Press
8. Spray Paint
11. Paper and Pencil
12. Angle grinder or Belt Sander(better option)
13. Disk sander
14. Spindle sander
15. Band saw with stainless steel blade
For a cleaner more advanced knife, you could try to get access to a mill or water jet cutter. If you can't your also gonna need a small flat jeweler's file or hacksaw blade to make the locking mechanism.
Now the materials:
1. 24" of Stainless Steel flat stock 1 1/4" by 1/8" thick, you could go thinner, but not too thin.
2. 1 Countersunk 8-32 x 3/4" Stainless steel screw
3. 2 Countersunk 4-40 x 3/4" Stainless steel screws
Step 2: Design
Now design your knife. You can make many different types of locks for the knife. Some are frame lock, liner lock, button lock, etc. But I'll be focusing on how to make a knife with a frame lock. Draw it all out on paper, mark the holes and slots and cutouts, then cut it all out to test fit everything and make sure your lock works. Also make sure there is no gap between the lock and blade. And don't forget to design an end piece so the blade stops when its folded, make sure its a little oversized so it ends up flush with the handle after you sand it.
Step 3: Desgin Transfer and Basic Cutout
Now your gonna put the design onto the metal. You can do this any way you like best, but I found that taping it from the underside and spray painting it directly over the top worked best.
Next we're going to cut out the basic outline with a bandsaw. Make sure you try to stay as close to your lines as possible, but if your having trouble just give yourself some extra room, you can always file or sand it off. Do not try to cut the locking mechanism yet! It could cause the whole knife to have way too much play and be pretty hard to cut with, if it isn't done right. And don't forget to leave two flat sides before you drill the holes. Otherwise your going to be stuck with a challenge to clamp it in the vice.
Step 4: Drilling, Fitting, Testing, and Tapping
Now these are critical to get lined up right, so be careful and slow. Drill out the hole marked on the blade from the spray paint with a smaller drill then a #29 drill, make sure its centered on the blade first though. If the mark got rubbed off, then just realign the paper up with the blade outline and make a mark with the awl, then drill it out. Next line the blade up with the lock and the frame on the locking side of the handle then mark the where the hole is through the blade's hole. Now clamp both handle pieces in a vice on a drill press. Make sure both ends are lined up. Then drill through both at the same time so the holes are lined up. Next, put a smaller screw(or a piece of metal rod the same size as the hole) through the locking side of the handle and the blade's newly drilled hole. Also make sure that the locks edge mark is a little bit beyond the back edge of the blade.
Now the end stop in the back needs to be drilled. With the blade still attached to one side of the handle; fold the blade as if it were "closed", then place your end stop up against the edge of the blade and mark where the stop overlaps the back edge of the handle. Then measure about a 3/32" from that line towards the inside and mark two holes about 1/2" apart lengthwise on the 3/32" line then drill them out with a #32 drill. Then line it up with the "closed" blade again and mark those holes on the handle. Now line the holes for the blade on the handles up with the metal rod or screw and then clamp them in a vice and drill both sides out with a #43(or 3/32") drill. Then drill one side of the handle out with a #32drill and the blade pivot hole on that same handle piece with a #18(or 11/64) drill.
Now comes the painfully slow part. First clamp your handle piece with the smaller holes in a vice, then take new or close to new 8-32 and 4-40 taps. Then tap the respective holes; the 8-32 for the blade pivot hole, and the 4-40 for the end stop.
Remember you need a SHARP tap since we are tapping stainless and this puts a ton of strain on the taps and could very possibly break it. This would ruin your nice new piece and your tap so be careful, especially with the 4-40. so go very slow, painfully slow with lots of cutting oil. And make sure that the tap is straight. If it isn't it could put extra strain on the tap and make the handle out of alignment. Please don't forget this!
Once thats over with, you can move on to countersinking the handle piece that wasn't tapped. But first put the handle together and mark which side is on the outside, so you don't countersink the wrong side. Then take a small countersink and only do a little at a time and test it with the screw each time. Your going to want it just barely recessed so when you finish sanding it it will be flush with the surface. Then do the same with the pivot hole, only with a larger countersink.
Step 5: Lock Cutout
So now comes the complicated critical part; the lock cutout. This may seem simple but if done wrong could ruin the whole knife so be careful again. Ok, so there are multiple ways to do this. The most professional and cleanest way to do this is with a water jet cutter, but since not many people have access to one I will cover the second best alternative, machining. I did this since I have access to a mill. And also a description of the simplest way to do it.
A little info before you start:
Since this is going to be different on every design I will only give a simple summary of how to do it. If you have access to a mill I will guess you have some know-how of how to operate it and if not I suggest at least looking up some instructional videos first before you start.
Even though this is a reasonably simple project on a mill, if it is your first time working on a mill or with stainless then I suggest practicing on aluminum first then with some scrap stainless before you tackle this.
Now enough with the info, on to the actual project. Now you can either thin out the lock or leave it the thickness that it is, I suggest taking off a couple of thousandths(of an inch), but don't take too much off because then it might bend or break when you are using it. If you do decide to thin it out, remember to leave at least a 1/4" on the side that locks the blade the original thickness so it'll lock the blade securely.
Next your gonna make the slot on top with the smallest mill end you can find. Remember to make it at least an 1/8" above the top of the pivot hole. Otherwise the blade might fold backward. Then make the slot for the actual locking edge make sure to make it so it overlaps the back blade edge just a couple thousandths so that the lock is secure. You can always file off the extra. Remember that with very small mill ends they break very easily. Your going to have to go really slow so take it easy and don't try to cut the slot all in one pass. Take multiple small passes.
Cutting with a File and Hacksaw Blade
These are the simplest methods, but not the best. But if you don't have access to a mill or water jet cutter this is your best option.
The first step would be to mark where your slots will be. Then take an awl and a ruler and mark a straight line down the center of both slots. Then take a 1/16" drill and drill as many almost connecting holes down the lines you marked, as you can. Then take your hacksaw blade and cut through all of the parts that didn't get drilled out. And finally clean it up the edges with the file.
Step 6: Filling, Sanding, Sharpening, and Polishing
Filing and Sanding
Now your going to finish cutting your handle shape out. Then to the final filing and sanding of both the handle and blade so that you have a smooth surface all the way around and so that the shape of the handle is right. Remember to use a disk sander for the outside edges and a spindle sander for the inside edges if you have access to those tools, otherwise just use a file and sandpaper on a flat surface.
So now on to the important part. So this can be done many ways. But I'm only going to cover two of the best ways that I know; using an angle grinder which creates a more convex rounded bevel, or using a belt sander, which is the professional way, and making a flat bevel.
Using an Angle Grinder
For this method your going to need a grinding disk and a sanding flap disk. The first step is to find someplace to clamp the blade to, like a table. Then use a C-clamp or bar clamp to secure the back of the blade to the table. Make sure the clamp is 100% tight, if not your knife could go flying, and no one wants that. So keep the clamp tight. Now to the actual sharpening. Take your angle grinder with the grinding wheel. Pick a very slight angle and slowly with steady pressure start from the back of the blade and work your way to the tip, check periodically and repeat till the sharp edge of the blade is about half the thickness of what it used to be. So for a 1/8" thick blade it should be 1/16" thick on that edge. Then flip the blade and repeat on the other side till the edge is sharp. Don't try to get it perfectly sharp yet. You can do that with a sharpening rod or sandpaper if you don't have one. Next is to smooth the surface a little so it'll be easier to sand and polish later. Take the angle grinder with the sanding disk attached and follow the same angle as you did with the grinding disk. But this time don't try to thin the blade out as much, you're just taking out all the grooves and scratches the grinding disk caused.
Using a Belt Sander
This is the simpler and more professional way of the two. But since it is more likely people will have a angle grinder than a belt sander, I'm covering both ways. Now the first step is to get some rough sanding belts for your sander (like 40-80 grit) and a couple of lighter grits (like 100-220). Then start with the heavy grit belts and start to grind a bevel in the blade. Keep a bucket or can or something full of water nearby so you can periodically dip the blade in it when its starts to get hot. Also check the edge of the blade periodically to make sure you don't go past the halfway point. When you get to the halfway point, flip the blade over and do the same on the other side till you get a sharp edge. Then switch belts to a finer grit and then sand all of the lines from the previous grit out and do the same till you get down to around 220 or higher grit. Then it's on to the hand sanding.
Hand Sanding and Polishing
This is the simple part. You're going to need sandpaper from grits 220-400 and waterproof 400 or "polishing paper"(if you want to polish it). Then start by taking the 220 and sanding lengthwise along the blade. And repeat that with finer grits till your down to the 400. Once you finish sanding with the 400, take the waterproof 400 grit and get the blade a little damp and sand it lengthwise as before with the waterproof paper. Or the simpler way, is just to use polishing paper and you won't have to use the water and the waterproof paper.
If you are having trouble taking out the lines from the last grit, change the direction your sanding, to diagonal to lengthwise. And change the direction each time you change grits till you get close to 400 grit.
Sanding the Handle
To sand the handle take full sheets of sandpaper from 50-220 grit. Place the paper on a flat surface and sand the side of the handle, so you get a flat and smooth surface on the handle. Again repeat the same step with finer grits till you get to 220. I only used 220 as the finest grit because it leaves a small amount of grip but still looks polished.
Step 7: Hardening and Coloring
Well the hardening is pretty important to the lock on the knife but isn't that important to the blade since we're using stainless which can keep an edge on its own. Though that's not to say that it does help it keep an edge longer. Coloring is just for style and looks.
This is a simple process that only involves a blowtorch with map gas. You could use a gas stove or BBQ but a blowtorch is a little better. Your also going to need a metal can with water or oil to quench the blade. Oil is better but a bit more dangerous due to the fact that it does burst into flames when you quench the blade, though it does usually put itself out once the blade cools.
Hardening the Lock
The first step is to grab the locking side of the handle with pliers. Then get your can of water or oil and go out into your driveway or someplace else that doesn't have many flammable things around. Then heat the whole lock to a bright red color. Make sure to get the base and the end the contacts with the blade as well as the main body of the lock. Then quench it as quickly as you can and make sure that it is cooled to the point that you can touch the lock. Do this process about 3-4 times.
If you are going to harden the blade then use the same process. But you only should heat the sharp edge of the blade to red, then quench it.
If you are going to color the blade, then as you might have noticed while hardening the blade that it will change within a rainbow of colors till it gets to light blue. Then it will change back to the original silver. So follow the same steps as hardening but wait until you get the color you want. Then quench it. That's it. You only have to do it once. If the color doesn't come out the way you wanted, just polish it off and try again.
Step 8: Finished
Put all the screws in and finish sharpening with a sharpening rod or sand paper and admire your new blade. You're done! Flip it in and out a few times and see how you like the feel.
Notes and Improvements
One major improvement I would've done and will do on my next knife, would have been to make an upper stop so the blade can't fold backwards. But the knife still works great either way.
Thank you for reading my instructables!