Making a Thumb Dagger - Inspired by WW2 Clandestine Daggers

Hi Instructables Community,

in this project I would like to share the making of an World War Two inspired clandestine thumb dagger. Originally these little daggers were issued by the British SOE (Special Operations Executive) and the American OSS (Office of Strategic Services) to their agents working behind enemy lines. These daggers were designed as a last resort weapon to surprise an enemy and maybe just buy enough time to make a getaway.

This design was inspired by the regular dagger types with double edges but I decided to go for a chisel grind as well as a slightly different beveled tip.

I did most of my research for this project on www.fairbairnsykesfightingknives.com/ which you might also find interesting if you have a general interest in knives and more specifically in fighting knives. Thank you to David Decker for for your suggestions and advice which I will use for future dagger projects!

Please also take the time to watch the embedded video as I made quite some effort to present the process for you!

In the last step I'm providing information on how you can support me (If you are interested that is) but I'm also very happy about any votes for contest I might get from you.

Cheers

Alex

Materials

1. Old saw blade preferably without carbide teeth - I did take some samples of this old saw blade previously to test whether the steel could be hardened with positive results.

2. Some twine or leather sewing thread

3. Leather strip as a lanyard but you could also use paracord for this

Tools (The products are linked through my Amazon Associates Account which supports me to make more content)

1. An angle grinder with cut-off disks, flap sanding disks & wire wheels
2. Belt Sander and or Grinder - This can be substituted by file work and lot of hand sanding if you do not have those tools
3. Cordless Drill with HSS bits - For more precision a drill press would be preferable
4. Whetstone

During my research I created a number of dagger designs for this project. For my first version I chose a design that was based relatively closely on designs used in World War Two but decided to add a few personal touches like a chisel grind and a steeper tip.

Now with a design chosen it is time to copy or print it out and cut it out so you can use it as a template for the following steps.

I chose to re-purpose an old saw blade as the material for this project. This saw blade was used a few times in the past to provide me with steel for projects. Although I do not know what exact type of steel it is I know from those previous projects that it will serve me well. Over the years the saw blade had become a bit rusty but that was only superficial and I was able to remove most of it with my angle grinder and a wire brush.

This step mainly serves the purpose to prepare the surface so the template will stick to it better.

Since I do not like to waste good resources I used the template to mark the area on the saw blade that was required to be cut off. To keep things easy and safe all that was required for now was one straight cut.

With the saw blade clamped down a 1mm cut off disk made quick work of this first cut. If you want you could also clamp down a sacrificial fence that can help you to make this cut straight. I prefer to do this freehand though which isn't too hard if you take your time use little pressure and let the grinder do the work for you.

You could use spray adhesive to do this but I prefer a simple glue stick to attach the template to the steel.

In this step I moved closer to the dagger outline by removing more material with my angle grinder. This step was done to make the shaping easier and save on abrasives belts. In hind sight I think I should have also removed further material with a flap sanding disk to make the following step easier.

To avoid cutting curves (which can be quite dangerous with the angle grinder) I recommend to prepare longer cuts by making relief cuts along the planned cut path that are perpendicular to that line. I usually make a cut every 5mm or so which works out fine for me. Be careful though to not move too close to your outline as those thin disks go through steel like the proverbial hot knife through butter.

I got myself a 1" x 30" belt sander for Christmas and now was the time to finally try it out on a project. I quickly realized that although it did remove material quickly I could or perhaps should have removed a little more material with a flap disk in the previous step.

Anyways using a coarse 60 grit belt removed the material quite effectively and I was able to move towards the outline quickly.

One thing I noticed however was that the design I used was completely hand drawn and resulted in a few asymmetric areas. I tried to square things up as good as possible and went on to the next step

To be honest this step should have been done way earlier and I recommend you to do it before you glue on the template.

The purpose of this step is to remove tool marks (from it's previous life as a table saw blade), dents and any other imperfections. This would be especially important if you intend to give the blade a mirror finish.

Initially I tried to do this with my belt grinder but noticed that the flat work area wasn't large enough and resulted in grinding in a noticeable dent. What followed was a long time sanding away with my old bench belt grinder until the dent was gone and another lesson learned. Using a welding magnet I was able to comfortably hold down the blade whilst not worrying too much about the heat (I did of course take care that the blade didn't get too hot).

An automatic center punch was used to create a small dimple which was then enlarged with a regular center punch. This dimple is very helpful for drilling because it helps the bit to stay aligned during the initial drilling. If not using a drill press it is likely that the drill bit will "walk" out of alignment.

With the blade prepared it was relatively easy to drill a 4mm hole using a HSS bit and a cordless drill. Going slow and using some cutting oil resulted in a clean hole.

Once the hole was finished I used a deburring tool to remove the burs around the hole. If you do not have such a tool you can also use a larger sized drill bit and remove the burr with that by hand.

Here is a trick I've learned some time ago from Laura Kampf. It is quite simple to make and costs next to nothing when made out of scrap wood. The only down side is that you will need a chop, table or miter saw to create an exact miter (Or you are skilled enough to achieve this by hand...or sorcery). I decided to go with a 15° bevel and see how it would turn out. The blade was fastened to the wood with a single screw which in hind sight was not ideal but more on that later. A second screw or other means of fastening would be preferable and I'm thinking of a number of design improvements (If you have any please feel free to post them in the comments.

I started this process with a 60 grit belt and the process was surprisingly quick and smooth. At this stage it becomes quite important to keep the blade cool to avoid ruining the temper. I did not plan to heat treat this blade so keeping cool was quite important.

I usually checked the process after each pass along the belt adjusting by hand where more material needed to be removed.

Did I mention to keep the blade cool? No? Right so when you see that the steel changes color cool it down immediately as this means that your blade is way too hot and the heat will change the physical properties of the steel in that area making it softer or too brittle depending on the temperature and type of steel.

Achieving symmetry by hand is quite the challenge. It helped a lot to move up to a 100 grit belt and continuing slowly. Also choosing to use a chisel grind made the whole thing only half as challenging as grinding four symmetrical bevels.

In this step I removed the remainders of the template and glue as well as giving the flat surfaces a rough finish on the disk and belt sanders.

This step is mostly clean up and was done with 120 & 240 grit belts. I removed any burrs as well as polished the edges and removed the 90° angle on the grip area to make it more comfortable to hold.

Using a whetstone and manually sharpening a knife is quite time consuming but the only alternative since I do not have appropriate power tools for this step. It is also a quite satisfying feeling to bring a piece of steel to razor sharpness this way.

So if you go with stones you will have to soak them accordingly. I usually keep mine soaked throughout the week and giving them time to breath during the weekend.

The decision to use a chisel grind came in handy during the sharpening as this type of grind is relatively easy to sharpen. Maintaining only one angle and then deburring the flat side was quite simple.

This step wont be necessary for most and I only did it for practice. The red stone is a 8000 grit polishing stone and was used to sharpen and polish the bevels as well as deburring the flat underside.

To remove any burrs and straighten the cutting edge the blade was finished by stropping it on a leather belt.

The blade is moved at an angle over the belt which polishes the blade. Other materials and compounds could be used for this step as well.

To test the sharpness of the blade I went for the paper test. The blade is moved along the edge of a piece of paper and if sharp enough cut thin & clean strips off of it.

Some of you might have noticed that I didn't do any heat treatment for this blade. This was mostly because my workshop setup didn't allow me to do the heat treatment at the time. This results in a "softer" blade which won't hold an edge for very long when used. This is however not a real concern since this type of blade is not an everyday carry item but a weapon of last resort.

To provide more grip I wrapped leather sewing thread around the grip area. I've attempted a criss-cross pattern for more grip but will have to experiment with that further.

In the pictures I tried to show how to form a loop though which the thread can be threaded and secured once the wraps are completed. Both ends would be cut off and the tucked under the wraps (Don't use a screwdriver though as it might scratch your finish, a toothpick will do).

An additional measure to secure the wraps would be to glue them in place with epoxy (which I didn't do in this case but will try out in the future).

Last but not least I attached a leather lanyard which would be used to pull the dagger out of its sheath (That'll be another Instructable) and as a means to keep it securely in your hands when drawn. It was tied with an overhand knot since I felt that a simple knot would complement this dagger more than some fancy decorative knot.

These daggers where worn and carried as a last resort means to overpower or surprise a guard or patrolling soldier. This could buy the agent enough time to either overpower his enemy or make a getaway. The small size allows the dagger to be hidden easily but makes it difficult to use safely which is however a minor concern in a fight over life and death. An agent could either hold the dagger between thumb (hence the name) and index finger or between fingers as a punch dagger to stab or slash an opponent.

I do not recommend however to actually carry this dagger around nowadays. It's legal status might get you in trouble depending where you are and there are other self defense options available today that might be safer for you and/or an attacker never minding the legal and moral consequences that would follow a stabbing.

Mine rests on my work desk and is now a nice letter opener and conversation starter.

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