Darker than Black Hei's Dagger Replica Project

Darker than Black Hei's Dagger Replica Metal Ver Rev2.5

Thingiverse:  You can download the STL from here to get the prop version printed - note that you will need to sand and paint the part yourself which takes some skill.

Project Overview
Not to be satisfied with other creations I've seen online, I set out to model Hei's dagger from Darker than Black with CAD so that I could have it accurately fabricated for me and easily reproducible.

Here's a rendering of the model I made - I used various screenshots and scans from the series as reference to make it look as authentic as possible.  The layouts that Volphin provides on his website were also a big help, though I did not follow them exactly and you can see the profile in my rendering is a bit different.

I am making a prop version that would be safe for bringing to events as well as a battle-ready metal version that Hei himself could use.  I've made the prop version an open design and anyone who wants it can download the model in .stl format at my Thingiverse.  If you want it in another CAD format shoot me an email and I can export it for you.

The metal version I made more or less exclusively for myself and a few friends.  I'm sure a lot of people would love to have one but few want to pay $500+ to have them custom made.

Please post any thoughts you have in the comments below!

Metal Version Rev.1
I commissioned Burdett Metalsmithing & Design to fabricate a battle-ready replica of this dagger with a 1095 high carbon steel blade and 6061 aluminum handle.  The dagger is fairly well balanced with a balance point within 1" of the guard.

As depicted here the metal version consists of three pieces held together by cleverly hidden flush rivets rather than being made of a single piece like the prop version.

The outer profile of the blade is first water jet cut from a sheet of 1095 carbon steel based on my provided CAD files and the bladesmith does his work to take care of the rest.  A similar approach is taken with the two handle halves.

The fabrication process for the metal version is quite involved and Burdett has provided me with step-by-step pictures of the process so we can see how it's done.  I have these posted below:

Darker than Black Hei Dagger - Metal Version Rev.1

Video Overview:  http://youtu.be/9OgEA-62LFc

I think that overall everything turned out fairly well. A better job could've been done with the powder coat masking as it looks a little bit sloppy around the transition from the blade to guard/handle; there is a slight bit of warping right around the tip of the blade as well due to the hardening process.  I also mis-estimated the scaling on this first run so the overall length is a whopping 20".


Metal Version Rev.2

I worked with QB Precision Technology Ltd. to create a Rev.2 part.   The handle halves are CNC milled out of 6061 Aluminum and anodized black; the blade is CNC milled out of 440C stainless steel and then hardened and sharpened.  Overall length is 16" and the assembly is glued together with strong metal glue.  This is obviously not as secure as using rivets, but this way you don't have to worry about hiding rivets and masking powder coating.  Overall weight is almost exactly 1 pound and it feels fairly hefty in hand.

I was pretty happy with the prototype unit and there are only a few minor issues which I would tell them to deal with if I ever decide to make a batch run.  I've posted plenty of pictures in the gallery below:

Darker than Black Hei's Dagger Replica Metal Ver Rev.2

Video Overview:  http://youtu.be/VQf9u-QfsY0


Prop Version
I looked into various fabrication techniques to see what yields the best results at a reasonable price for this version.  The prop version can either be made of a single piece or out of a three-piece assembly like the metal version.  The single piece is more economical but ends up being a bit harder to paint since masking various parts of it is fairly tricky.

The latest .STL file is always available for download at Thingiverse and you are free to do with it as you please.  Listed below are some of the fabrication techniques that I have or am currently looking into for this project:

Polyamide/Nylon 12 3D Printing [Selective Laser Sintering]
-Excellent durability; good flexibility prevents it from snapping under stress
-Rough surface requires heavy sanding and primer before painting
-Visible build layering effect throughout part
-Long and thin parts such as this one can potentially end up slightly warped
-One of the cheapest 3D printing materials

Video Overview:  http://youtu.be/UwZr99qxrCU

Polyamide is not as premium feeling as paintable resin and has a sandy/porous surface texture due to the laser sintering process but it's easier to post-finish and paint than 3D printed ABS.  It's durability and flexibility is comparable to that of paintable resin, and its pricing is fairly reasonable.

The full scale 3D print from Shapeways that I received looks fairly good but has a few visible defects on one side of the part. (due to removal of support material most likely)  The part durability is also very good though the porous surface poses a bit of a problem.  Paint applied directly to the part tends to get "bubbly" due to air being trapped in the porous surface.  I would recommend using a fairly thick sanded primer layer as a smooth painting surface if you want good painting results.  I neglected to do this on my prototype so it doesn't look that great.

Paintable Resin 3D Printing [Stereolithography]
-Excellent surface quality enables painting without much post-finishing
-Fairly rigid but can be snapped fairly easily when bent too much
-Visible build layering effect throughout part
-Too expensive even when produced in batches

Below are images of a 70% scale paintable resin 3D print I ordered from i.materialise along with a 35% scale prime gray 3D print just for kicks.

Video Overview:  http://youtu.be/Mjy07LSsJnU

My inexperience and lack of patience when it comes to painting things shows here; most of you guys can probably do a better job than I did.  I think the results are fairly good though given my lack of professional equipment and experience.

The properties of paintable resin make it almost perfect for the target application.   The surface quality / paintability make it possible to achieve a very good appearance.  The generated part is also fairly durable and its slight flexibility helps it withstand some minor abuse.  The density and feel of the material is just about right for a prop as well.

Unfortunately it is also far too expensive for the target application, and I also snapped the blade cleanly off of one when playing with it just after unboxing.

Resin Casting
-High part accuracy
-Excellent surface quality
-Mold requires high initial investment (~$600USD) but low price per part afterwards
-Slight shrinkage

This process would yield better surface quality and part accuracy than most 3D printing technologies at a lower unit price.  Unfortunately at the moment I'm not really willing to put in the initial investment to make a mold of this part, but it may be something I could consider in the future if there is the demand. (which I'm not seeing)

Here's a picture of the part I would use as the master for mold making.  It was CNC milled for me out of ABS plastic by QBPrecision Technology Ltd.

The copies would probably be cast out of something like Smooth-Cast 305 or TASK 3 resin from Smooth-On.  Resin casting is commonly used by prop makers so it's a tried and true technique and there are quite a few mold makers that could do the job for me as well.


Wrap-Up
So there you have it - a full project log of everything I've done and all of my findings undertaking this project.  I'm more or less done with it at this point as I'm happy with my current metal dagger and have already sold all of my 3D printed prototypes on eBay.  I'm pretty happy with what I've done and I don't really plan to do anything else with this project.  Thanks for reading!