Introduction: Alice in Wonderland "Talking Doorknob" Mold
"Sorry, you're much too big, simply impassable." "You mean impossible?" "No, impassable! Nothing's impossible"
Here I'll walk through my process of making the Talking Doorknob from scratch.
- Access to Solidworks (or some other 3D design software if you want to make your own)
- Access to a ShopBot for milling
- A large piece of wax (on the order of 6'' by 3'' by 1'' at minimum, but bigger is better!)
- Liquid Plastic
- Gold Spray Paint
- A touch of black and white paint (for the eyes)
Step 1: Modeling the Part in SolidWorks
Above is a peak at the progression from design to finished product.
High level steps are:
- Trace/design image in SolidWorks
- Import STL file into PartWorks 3D and mill into a piece of wax using ShopBot
- Use wax to make an Oomo mold
- Use Smoothcast liquid plastic to make the door decoration
- Spray paint/hand paint
I played around with my doorknob and determined that it most definitely could not be taken apart without cutting straight through the piece. Thus, I knew I'd have to mold two parts that could fit around the knob. I started off by making my model in SolidWorks. I imported an image of the character and traced it, then extruded in varying degrees.
Note: To trace an image in SolidWorks, create a new sketch and then import an image of your choice via Tools->Sketch Tools->Sketch Picture. You can then use the standard drawing tools to sketch over the image.
Alternatively, you can just use my Solidworks file (AUGUST 2016 UPDATED LINK: https://www.dropbox.com/s/w4diswk5mksqgdl/doorknob.SLDPRT?dl=0) , if you give me credit :)
I hoped to add more texture than Solidworks allowed, so also played around with Autodesk's Mudbox (first image above), a truly remarkable program that lets you push and pull meshes around like a block of clay! Although I had a lot of fun playing around, I worried that the design might come out looking messy, and so ultimately opted to print the flat version and save some more subtle work with Mudbox for another time. [Pro tip: if you'd like to use Mudbox with a SolidWorks file- you'll need to use Meshlab to convert from STL to OBJ formats).
Step 2: Milling the Part on Shopbot
As you can see from the photos above, I milled the two parts at the same time in case I needed to make small adjustments to the wax by hand to fit the doorknob properly (this turned out not to be necessary).
I used PartWorks 3D for image processing and a 1/8'' ballnose endmill for cutting.
The basic steps are:
- Export STL file from SolidWorks to PartWorks 3D
- Setup your part (1/8'' ballnose is a good choice to get a smooth, curvy finish. Don't forget to offset your object from the top plane so that you can make your Oomo mold!)
- mill part into a block of wax
If you're experienced using the ShopBot you should not have a problem! But here are some troubles I ran into:
My side borders were far too fine, and as a result were completely cut off. I also forgot to add some depth to the cut. I ended up recutting right below my original cut, but at the bottom you might notice that somewhere in this process I accidentally cut a bit more deeply. I tried to repair the piece with hot glue, which turned out not to be the best solution since it left some unwanted texture to the doorknob's chin. Fortunately It's not extremely noticeable! I might have been better off repairing with putty, but couldn't find any around.
Step 3: Making the Mold
Since my walls were cut off, I had to use some plastic scraps as makeshift walls wall constructing my silicone mold. They were easy enough to attach to the wax mold. I made my Oomo mold (fun!) and then cast in SmoothCast plastic. The pieces turned out great! I bought some gold spray paint from Artist and Craftsman and spray painted the pieces.
Don't forget to poor the Oomo and the SmoothCast in a very fine stream way above your mold (this helps to prevent bubbles from forming.)
Then I borrowed some black and white paint to paint the eyes. I was so eager to assemble that I didn't let the paint dry enough! Be patient with spray paint :)
Step 4: Attach to Doorknob
Finally, I hot glued the pieces onto my doorknob. It would have been better if I had managed to take apart my doorknob and do a one pieces mold. Another option would be to 3D print or mold/cast a piece for the back of the face so that it sits more cleanly on the knob. But for my immediate purposes, hot glue worked just fine.
And there you have a talking doorknob :)
(Bonus project: add some electronics to make it actually talk when you touch the doorknob !)