Introduction: Functional Mjölnir Prop - Carpentry Section
Recently one of my friends showed me the brilliant video of the "Mjölnir" by Sufficiently Advanced.
It's a great idea and they really made an excellent prop, however, we figured that if one would like to bring such a prop to a costume party a more compact and lighter version of it could be more convenient. With the carneval-season right ahead of us, we decided to have a go at building our own.
The Key features of this version are:
- compact and light construction
- "partyproofe" design
- long battery life
- RFID based identification
- carving knives and chisels
- bow saw (basically almost any saw that is good for curved cuts will do)
- carpentry square
- scrap wood (plenty)
- wood glue
- 4 threaded inserts with screws
- metalic spray paint
- black spray paint
- transparent paint (I've used acrylic)
- duct tape
This instructable is soley dealing with the wooden base construction of the Mjölnir, not with its inner workings and the electronics involved. I'm currently working on writing a separate instructable on that one, so stay tuned. Please also consider supporting me in the contests I've enrolled.
Step 1: Building Mjölnir's Carcass
Instead of fitting the electronics inside a commercially available Mjölnir we decided to build our own. Mostly to allow us to tailor the design to the available components. The reason to chose wood over other building materials was simply due to its availability.
The carcass makes up the hammer head an serves two prime purposes. Firstly It needs to hold the electronics and needs to be big enough to house the electromagnet. Secondly it needs to be rugged enough to to stand the stress of a grown man pulling on its handle. The solution was to fit the magnet and the electronics on a central blank that is permanently and firmly attached to the handle. This contraption is fitted into a carcass made up of much thinner material. Since this outer shell doesn't needs to contribute to the overall mechanical stability, this is no issue. In this work I figured out most dimensions as I went, so stick to what ever materials you have at hand.
The carrier blank is out of 25mm Spruce that is joined to the handle using a dovetail. Since it is solely a functional joint I formed it quick and dirty by cutting the shape of the dovetail using a bow saw and chiseling out the waste. The weakening due to the cuts is compensated later on by adding a strain relief block on top of the blank.
For the housing I picked up some 12mm thick scrap boards I salvaged from pallets earlier. They are quite though and lend them self somewhat well to carving, a necessity in ornamental works like this. They can easily by squared up using a handplane and a shooting board. The front and backside is made out of cutoffs from the carrier blank. This ensures the carrier Blank will fit snug within the housing and avoid the needs for any measurements or fiddly fitting. Just cut the blanks roughly about 5mm oversized which allows for easy trimming to a perfect fit after the glue up.
The handle is made of some Ash scrap wood I had laying around. This part is also not critical, It just have to be long enough to be useful, thick enough to alow for the dovetail and sturdy enough to withstand someone pulling on it like crazy. Cut the dovetail but have it deliberately over-length. Finding the length that just looks right is much easier after the glue-up of the housing.
Step 2: Gluing Up the Carcass
Using a shooting board to ensure square ends of the boards eases this step significantly. To get nice square corners in the glue up, just line up the ends of the housing boards around the carrier blank. The oversized boards provide some wiggle room for positioning all the parts. Glue them up with plenty of glue and clamp all parts firmly. Now it should look something like in the pictures. Any overhang is easily removed after drying using a hand plane. Since the front and back piece are cutoffs of the carrier blank, they have the same width as carrier blank. So blank will fit perfectly into the housing without taking a single measurement. Nevertheless some fiddling around is integral part of the experience ;-). Some last warm heads up at this point, don't glue the bottom of the box shut, this will be lid maintaining the electronic within the contraption.
This glue up consist mostly of butt joints, however, rigidity is not the prime concern here so that should be fine.
After drying the corners are trimmed using a hand plane. and the carrier blank with the attached handle blank is inserted into the carcass. At this points one gets a first impression of the final size and it allows to take measurements where the handle and the magnet needs to protrude the carcass.
This is the only step in this build when you need to grab a pencil and a ruler in order to mark the desired openings. After laying them out on the housing, I've removed the material using a chisel, however, a jigsaw could also be used.
It is a good idea to chamfer the edges after the layout of the openings. This makes for easier measurements and layout since you still have crisp corners on that thing. A lesson I've learned the hard way ;-) . This is also a good stage to decide on the final length of the handle. Take some pictures of you holding the prop so that you get a better feel for which length looks reasonable if you don't feel confident just eyeballing it.
Step 3: Preping the Surface and Carving
This is the perfect moment to fit the lid of the hammer head to the rest of the head. Use a shoulder plane to cut a rebate around the lit so it will fit snugly onto the box without wiggling. When it is seated mark the correct orientation of the lid in respect to the head and drill all four in one go to ensure a perfect fit. Since You need to access this compartment regularly when changing the batteries and so on, the threads should not wear out easily. Therefore, using threaded inserts (see the picture 2 for the ones I've used) is surely the better option than solely relying on wood screws for this.
At this point the Mjölnir's head got its final shape, although, in this state it still looks very wooden. By applying a water based filler and some sanding the surface can be evened out. Since all surfaces are rather plane anyway, this step is rather easy. However, avoid very thick layers of fillers since they are prone to cracking when it dries.
This thing is based on north European mythology right, so it definitely needs some Celtic ornaments. Sketching out the desired layout with a pencil helps a lot to get the proportions right. Since it will be spray painted any way we don't have to worry about pencil marks.
For the carving itself I used a carving knife and a 5mm round carving chisel. I guess a multitool with a small ball rasp could also do the trick. Anyway, don't go crazy with the surface finish of the carving. I just cleaned it with some steel wool.
Step 4: Adding Wings to the Handle
In a next step I turned the handle round, to give it a more finished look. How you choose to round over the square handle is not very critical and If I'd ever make a second one I'll probably carve it.
When playing around with it at this stage I found out that I'll need a larger flat surface on the handle to house the RF-ID reader. Additionally, I need the user to grab Mjölnir it in a rather deterministic manner for the capacitive touch sensor to work properly. So I figured, some bat like wings wouldn't violate the design and their pointy ends should encourage proper handling by the user.
Luckily I've had some ash scraps in the correct thickness. I've used a bow-saw to cut out the shape and a rather aggressive rasp to profile the outline. Since the wings can be stacked during profiling, achieving a perfect symmetry is rather easy. I've chiseled some flat surfaces onto the sides of the handles to provide a good glue surface and glued the wings on.
After the glue dried, I chiseled out some recesses for the RF-ID reader PCB. This results in a flat surface when the PCB is installed. But more about this in my instructable on the electronic part of this project.
The wedge like profile of the wings was shaped using a handplane. This works surprisingly quick and marking out a center line ensures a symmetric result.
Step 5: Carving the Wings
Now its once again time bring out the carving knives. Firstly, I started with hollowing out the curved sections using a 15mm carving chisel to 90% of the final depth. Then I switched to caring knifes and started to form the ridges and used the rest of the material to blend this two features together. Some sanding is mandatory, however, since carving leaves a rather nice surface din't took long.
Step 6: The Paint Job and Assembly
In order to give Mjölnir's head an authentic metallic look I've primed the surface using a sliver metallic spray paint. After three coats and I made sure I've covered all the features also within the carvings I hit it with some light puffs of black spray paint. Do that form a shallow angle instead of dead on, that will provoce uneven depostion of this darker paint and give your design greater depth, especially at the carvings.
All other wooden parts got some swift coats of water based transparent acrylic just to protect the surface form greasy finger prints and spilled drinks.
At this point I've decided to go mad on this project and add EL-wire to the carvings in order to illuminate them when It is in the hand of a person wearing a valid RF-ID tag. This just called for some tiny holes to be drilled and some hot glue to keep it in place.
To cover the RF-ID reader the capacitive-touch and all other electronical bits and pieces, the handle was wrapped in duct-tape. Not very elegant, however, the somewhat slippy surface and the water repelling property of this stuff really serves the functionality of the overall concept.
Step 7: The Final Assembly
When all the carpentry work is done , one still needs to add all the electronics and write some Arduino code. Since this is a story of its own I'll cover that in a separate instructable dealing with the electronic part of this project.
Thank you for reading my instructable and have a fun time recreating this project. If you have any suggestions or questions, feel free to contact me using the comments.