Hack a Swiss Army Knife to Have a Carbon Steel Blade

OH how I love my Victorinox Forester SAK. It has everything a resourceful and civilised gentleman should need in an Every Day Carry knife, such as a corkscrew. One thing that isn't quite great though is the quality of the steel used for the blade. Stainless steel looks good, but - for most types of SS - that's about it. Its edge is lost as soon as it gets good use. Carbon steel, however, holds a great edge for much longer. The other thing about the Victorinox blade is that the shape of the blade ("the grind") has a long taper with a secondary bevel - really I prefer short single bevels ("scandinavian grind" or "scandi" for short) which is personal taste but it is very easy to sharpen in the field.

I looked at other knives to see if there was anything out there with similar features to the Forester but with a carbon steel blade. Nope.

I looked out there to see if any clever cutlers are making retro-fit, aftermarket, Carbon-steel Scandi-grind Victorinox replacement blades. No such luck.

So, armed with some YouTube-learned metallurgy, and my Dad's garage (which is set up for metalworking, as opposed to mine which is set up for a band) - I hacked it.

This Instructable will work fine with most types of SAK although the method of mounting/hinging the blade and removing the scales might vary. If your SAK has a non-locking blade then the hack is MUCH easier since you don't need to worry as much about getting the "tang" exactly the same as the original - for the (locking) Victorinox Forester the tang has a "liner-lock" [wikipedia] which means the tang has to be very accurate for the locking mechanism to work properly, if at all.

MATERIALS:

• STEEL - I measured the thickness of the existing blade: 2.4mm at the thickest bit. I couldn't get tool steel in this thickness so I settled for 2mm and figured I would have to use a washer/spacer. I got "O1 Ground Flat Stock" - about £10 from eBay, and I still have LOADS left to do other tools with!
• PIN - during dismantling you will remove the hinge pin which is a 3mm diameter brass pin which is caulked over (hammered) on both ends and has a little round ferrule around it (difficult to describe, and so small I couldn't really get a good picture, you'll just have to see for yourself) - when you remove this it will be useless so you will need some other 3mm diameter piece of metal - I used a 3mm diameter nail and it worked perfectly. It will rust but is probably stronger than brass.
• WASHER - as mentioned above I needed a small washer (see final assembly stages) which I had to make by cutting it out of a bit of 0.5mm brass sheet (cannibalised from the inner shell of an old carbon brush from a motor)

TOOLS:

• general metal working tools - files, vice, hammer etc
• gas torch for heating metal to harden it (but note that this can actually be done using a charcoal fire - see the GreenPete Knife Making Video)
• domestic oven
• optional extras that make life easier - bench grinder

KNOWLEDGE:
http://vimeo.com/album/1577465
I found this great video a few years ago which shows how you can make a bushcraft knife out of an old file in the woods. This guy is great and I cannot thank him enough for putting this video together, it is quite incredible what he manages to do with virtually no equipment - I felt mildly embarrassed about the fact that I used something so unmanly as a gas torch for the hardening process!

• Prise off the scales (plastic handle pieces) with a sharp-pointed screwdriver or similar tool.
• There is a brass pin on which the blade hinges. File off enough of the brass pin on one side so that you can pull it out the other side. The knife blade should fall off. On the Victorinox Forester SAK, the wood saw blade and the tin opener will also fall off. Other SAK's may be different. The removed pin probably isn't any use now, you will need something else to make into a hinge when rebuilding the knife.

In an attempt to be all 'geek' about it, I tried to scan the blade into JPEG format and then edit the shape using GIMP. Unfortunately, due to my lack of skill in this area it failed miserably, I could not satisfy myself that the digital tempate was EXACTLY the same size when printed as the original. I couldn't really be bothered to spend any more time on it as I was eager to get my new blade done.

So, I did it the Old Navy Way, copying round the original blade with a scribe, direct onto the tool steel blank. I added a thumb hole to enable one handed opening (see later) - giving the blade a definite Spyderco look - in the end for various reasons I ended up changing the shape back to the normal victorinox blade shape after experimenting with a thumb stud (see pics)

I then cut this shape out with a hand saw and did the final work with a grinder, getting it pretty close to the original.

Then I located my pivot hole on the new blade and drilled it - since this point is the most important bit of the whole blade.

Once that was done I essentially riveted the old blade and new blade together through that hole, once fixed in this way I spent a bit of time filing so the two were IDENTICAL. The most important bit to get right is the EXACT shape of the tang, as this is crucial in getting the linerlock system to work right.

After a bit of internet research I found that for a single bevel "scandi" grind you need to file an angle of about 12 degrees into each face of the blade, together this makes a blade with a bevel of 24 degrees.

Clamp the blade horizontally in a G-clamp, which is itself held in a vice (see picture)

I used a protractor to get a rough angle for the bevel, and then more or less did it by eye, making sure the bevel was similar both sides. I used a file although I think the "pro" custom knifemakers use a belt sander.

It's important to get all scratches and gouges out of the metal now before it's hardened, after hardening it will be a lot more difficult to remove any imperfections. I used a heavy/coarse file, then a fine file, then several gauges of sandpaper (finest was 240 grit). Then I buffed it on a buffing mop wheel.

I thought, since I was making myself a nice new blade and all, I could add a feature I really like on my CRKT knives - one-handed opening.

Initially I thought that I could do this by enlarging the blade and putting a thumb-hole in it (see Victorinox's own one-hand openers for what I mean) - you can see the intention in the initial blade-making pictures. However, when I actually tried to use it the hole was not really in the right place and it was harder to open than it was before!

My next attempt was to remove the metal bearing the hole and put a small stud in the blade for thumb-opening (like on the CRKT M16 knife) - all went well until I suddenly realised why this won't work on a SAK - the thumb stud obstructs the opening of the adjacent blades!!! DOH.

So I ground it all off and so now my blade is the same basic shape as the original. I left the back of the blade quite rough and with sharp 90 degree un-smoothed edges (where I had ground off the thumb hole and thumb stud experiments) as this will provide a striker surface for firesteels.

Serves me right for trying to out-clever the Swiss.

Once the blade was shaped right I did some sanding & buffing to make it nice. Then comes the fun part - hardening.

Basically the process is to heat the metal up to Very Hot, when it stops being magnetic due to a change in the crystal structure. Then you quench it cold very quickly by plunging it into some oil. It is now VERY hard, BUT very brittle. So you have to soften it a litte, a controlled softening, using an oven (there are other ways to do this but I thought the oven would be most consistent). This creates a blade that is hard enough to stay sharp, while being much less brittle (so it won't shatter of you drop it like a file would). Depending on the temperature you use to temper it, you can make it varying degrees of hardness, I chose 250C as it is supposed to result in a Rockwell Hardness of about 58 (ish) which is meant to be about right for a bushcraft knife.

There are people on the Internet who actually understand this and there is loads of information out there so I will let you get any further information you require from the Green Pete Knifemaking Video and from other Internet sources, I'll just stick to describing what I did.

1) Preheat your domestic oven to 250 Celsius. In fahrenheit that is 482 F.

2) Holding the blade in locking pliers, heat up with the gas torch until cherry red. Then start checking with a small magnet if it is still magnetic. Once it loses it's magnetism the structure has changed, hold it at this temperature (judged by colour I suppose) for a few minutes, then plunge into a bucket of oil AND COVER IT (in case it flashes into fire!!!)

3) Remove and wipe down. Sometimes the metal has distorted a little from this process, mine acquired a small twist to the left less than 1 degree and I was happy to ignore this. I suppose if it was worse you could try re-heating it to above the critical temperature again and re-quenching but I'm not sure if this causes weakening.

4) Stick it in the oven at 250 C (482F) for 2 hours, then switch off and allow to cool slowly.

5) Sanding and buffing again, to remove all the black stuff!

As I mentioned earlier you will need to make or find a small washer to make up the difference between the 2mm tool steel blank and the original blade which is about 2.4mm thick. I cannibalised a piece of brass plate that was about right and drilled a 3mm hole, then cut a circular washer using tin snips around this hole, so that the final was about 8-9mm diameter.

Then it's just a case of putting everything back in the same order it came off and using a new hinge/"axle" (I used a plain steel nail that was exactly the right diameter - 3mm)

Cut the nail (or whatever you've used as the axle/hinge off) so that about 2mm sticks out each side of the knife.

Caulk this over using a hammer, I would advise repeatedly checking the friction on the blade while doing this - you want it tight enough that there is very little lateral wobble on the blade, however if you make it too tight it will be hard to open the blade. Experimentation is the only way. If you go too tight you can always saw one end of the axle off, pull it out and do it again.

I was very happy with my result and can report that the lateral "play" or wobble is no worse than with the original blade.

Clip the scales back on, and youre done

Clean blade, sharpen blade & oil the hinges and you are done.

possible future instructable:
It would be very easy to make a set of nice decorative wooden scales by copying the shape of the plastic ones and then gluing them on with some good glue like evostik contact adhesive.