Introduction: The Urban Micro-Knife

There are zillions of knife-making instructables out there, but how many of us have a propane torch? Let along a forge.
And to be honest, I don't need a 20cm long knife that's indestructible.

All I need is a knife thats:
 - Fits in my pocket
 - Easy to make if I lose it
 - Can cut paper, string and peel oranges.

Enter the Urban Micro-knife. A simple, easy-to-make knife that you can carry with you all-day, every day, and not care about till you need it.


Step 1: Idea and Concept

Once I had identified the need for me to make a knife, I laid down the set of rules to describe exactly what I wanted. They ended up as the ones on the first page: small, easy to make, but usable.
As all engineers know, understanding the problem is half of the problem

So, knowing what I wanted, I started to draw.
In the fifteen minutes between getting in bed and turning off the light, I drew the first concept sketches (attached). Even in this age, paper remains my favorite way of generating ideas.
I also applied some thought to materials. 
The blade was easy, that sharp angle matches the one found on a craft knife blade, and the handle I figured I could make from any thin metal.

I continued finalizing the concept on the computer the next morning, producing two CGI images, which I could then use as reference for dimensions.

Step 2: The First Prototype (and How to Make Tube-Rivets)

This one was a real quickee to test out the functionality of the idea. Would a craft-knife blade be strong enough? Are the angles too angular? How does it look, and is it too small to be useful?

So, in 45 minutes I assembled a knife. I didn't make any plans, I just eyeballed everything. An old craft-knife blade snapped off to 5cm long, the end with the hole rounded nicely on a grinder, and the handle made from coke can.
At first I left it in coke-can silver, and without the cutouts, but then I painted it black and made the cutouts. This left the handle weak, but it looked way cooler.

This prototype taught me a lot. It showed me that I needed to allow for space for the blade to open out fully. It proved that the notch in the handle exposing the blade did allow you to cut string (and open letters, if you ever get any), and, most importantly, it let me know that the blade was indeed strong enough for a small knife like this.
I carried it around for a day or two in my pocket, and used it a couple of times. This really sold me on the idea of making a version with a more durable handle than the flimsy coke can.


I also used this as a test for how to make tube rivets. A bold could be used, but it would add a lot of thickness to the knife, and not look that great.

Here's my mini-ible on how to do tube rivets.

Tube Rivets:
These things are pretty simple to make, as I discovered.
1) Drill a hole
2) Find a piece of tubing that fits snugly into the hole
3) Cut the tubing so it sticks out by a 2-3mm
4) Flare the ends of the tube using a nail
5) Continue flaring the ends of the tube with the round side of a ball-pein hammer.
6) Using a flat-faced hammer, finish it off leaving it nearly flush.

I may make a proper Ible on these one day, as they are a very easy way to join two bits of metal. They are nearly as simple as, and (in my mind) look better than pop-rivets. They also don't have a sticky-out catchy bit to tear at your skin.

Step 3: Materials and Tools for Version 2.0

After the prototype, I knew the idea was good, and all it needed was a stronger handle material.
I paged through my stocks of aluminium and pulled out a section of some 1mm sheet.....
I also drew up an outline, though I never used it.

Cost:
- $3.75 for ten blades
- $? for 1mm aluminium (0.5mm would be better)

Time:
- 1 hour

Materials:
- 0.5-1mm sheet metal (I used aluminium, because I had it)
- 3.5mm exterior diameter tubing (I used brass, because I like the color)
- Craft knife blade 
- If you have it, a very thin oil (I used Trumpet Valve oil, my standard for anything small)

The materials aren't fussy. If you don't have brass tube, use aluminium, steel or whatever you have. Or just use an M3 bolt. No aluminium sheet? Copper or steel would probably work, or, if worst comes to worst, Aluminium Coke Can wasn't too bad (plus you get to drink the coke).

Tools:
Needed:
- Sandpaper
- Ball-pein hammer if you want to tube rivet it
- Something to cut your sheet metal (I used a junior hacksaw)
- 3.5 drill bit (and a drill of some sort)

Useful:
- Bench Grinder
- Disc Sander
- Drill Press

Things that may be used, but I didn't:
- CNC (for cutting the handle)
- 3D printer (I don't know what for, but people use these for everything)

Step 4: Shaping the Blade

Unfortunately, craft-knife blades aren't ideal. They have a few quirks.

Snap
Snap off the blade to the right length. V1 had a 5cm blade, V2 has a 5.5cm blade. Take your pick, it doesn't really matter.
Clean up the snap with sandpaper or a grinder.
- Don't snap it with your bare fingers. Guess what happens.... Be nice to yourself and use a pair of pliers.

Round the back
The back of the blade is angled at about 30 degrees. As I'm sure you realize, this won't rotate nicely when mounted, so we have to round it.
I used a bench grinder, and it worked fine, but here are a few hints:
 - Don't cut or burn yourself, work slowly.
 - Don't de-temper the metal by letting it get to hot. As I said before, work slowly.

If you are using sandpaper, it will take a while. You can speed it up by snapping little sections off with a pair of pliers, but it easy to make a mistake. Then again, a blade is only 38 cents.

Step 5: Folding and Making the Handle

Folding and shaping a coke can is easy, I did it with my hands and a pair of scissors. 1mm Aluminium is a little harder, though not much.

Folding:
It is much easier to fold it in half first, so the sides are identical. To do this, insert a few centimeters into a vice and fold it over to 90 degrees. Take the sheet out of the vice.
Now comes the nifty bit. Put the blade into the corner, and fold it right over. You should be able to do this by hand, resting one side down on something.
Now hammer the corner lightly to get it to stay folded right over.

Because the blade is inside the fold, there is a blade-width slot! You may need another blade to get it out though.

Shaping:
- Draw
- Cut (with a hacksaw)
- Smooth (with sandpaper, a disc-sander or a file)

Drilling the hole:
Because the hole in a craft-knife blade is not central, take some care when deciding where to drill. You want the hole to be so the blade will open exactly 180 degrees. I used these steps:
- Place blade in slot, in the open position, right where you want it
- Memorize where it it
- Place the blade in the same position, but on top
- Mark where the hole is.

Now center punch and drill the hole with a 3.5 drill bit

My drill-bit was blunt, so where the hole was, the aluminium melded together inside the slot. I used the blade and simply cut through this. After all, aluminium is soft.

Step 6: Putting the Two Together

I used a tube rivet, as described in step 2. Other alternatives are a bolt, which is easier, but far bigger and likely to loosen. And honestly, a tube rivet isn't that hard.

For those that don't want to got back to step 2, I've copy-pasted the steps here:

Tube Rivets:
These things are pretty simple to make, as I discovered.
1) Drill a hole
2) Find a piece of tubing that fits snugly into the hole
3) Cut the tubing so it sticks out by a 2-3mm
4) Flare the ends of the tube using a nail
5) Continue flaring the ends of the tube with the round side of a ball-pein hammer.
6) Using a flat-faced hammer, finish it off leaving it nearly flush.

Step 7: Painting and Finishing

Humbrol Super Enamels are amazing.
These were bought ten years ago, and are still fine. Most aren't more than half empty either.

Painting:
- Round the corners slightly
- Stick it in a cork
- Paint it

The first knife I did gloss black, and the second, mat red. Do whatever color you like.

Oiling:
You may notice that it's a little stiff to open, because it's a snug fit with the case. This is good, it removes the need for a latch of any kind. Mine was a little tight, so after the paint had dried, I oiled it with the lightest oil I have: Trumpet Valve Oil.
The easiest way to get oil into the handle is with another blade. Put a drop or two of oil on a fine blade, and touch it to the crack between the blade and the handle. Watch as capillary action sucks the oil into the knife. This is a useful technique in other cases as well.

Now we can call our knife done, at least for now.

Step 8: Evaluation

I'm pretty satisfied with the knife. It fills the design requirements: small, light, easy to make. 
This one is a real keeper. V1.1 lives in my wallet permanently now, and V2.0 is often in my pocket.

I'll probably add the cutouts to V2.0 sometime in the future, after Uni Exams, and I may well make a few more, perhaps using a thicker blade. But who knows? I'm pretty satisfied.

Comments

author
urill made it! (author)2013-05-27

There are a lot of this kind of knives where I live, usually sold for 5 cents USD each, for sharpening pencils. Maybe you can make one with a 3d printer.

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author
dan3008 made it! (author)dan30082015-10-27

sorry to resurect a 2 year old post, but what are those knives called? I'd love something like this for pencils ect... That or I might have to design my own with a 3D printer, and Stanley knife blades lol

author
sdfgeoff made it! (author)sdfgeoff2015-10-27

Funnily enough, I thought of this ible yesterday. I'm thinking of re-doing it slightly differently.

You can make a similar knife from:

- A craft knife blade
- A piece of aluminium coke can
- An M3 bolt and nut

Fold the coke can, cut it with scissors, punch a whole, insert blade, put in bolt.
It takes about 3 minutes.

author
sdfgeoff made it! (author)sdfgeoff2013-05-27

Huh, we don't get those here (New Zealand), and if we did, they'ed probably be at least $4-$5....

author
Schmidty16 made it! (author)2013-05-30

and if you wanted to make it have comfort use surgru

author
Gregbot made it! (author)2013-05-26

nice and thanks!!!

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