Talking on your cell phone can be a dangerous affair. Better arm yourself with some kind of defence in case someone tried to tangle with you while you're gabbing away. What better way than to combine a knuckleduster with a phone case! You may have seen these neat "knuckle" iPhone cases, which is an iPhone case within a knuckleduster. However I wasn't a fan of the $99 price tag, so I decided to make my own.

I have zero experience with any type of 3D modeling software. So, you can understand my apprehension when I wanted to make my own custom 3D printed object. Luckily there was a very detailed Instructable already written on how to make your own action figure that outlined the process, showing that mashing up existing 3D models is easy. Making my own custom 3D model was so simple I was able to make my model in about an hour on the computer.

This project uses the free modelling tools Netfabb, and MeshMixer. I printed my model through another service, but there's currently an offer through Instructables to print a model for free! You could make your own for almost nothing! How great is that?!

Step 1: Find Models and Convert With Netfabb

After a quick search online I found 2 free models on Thingaverse:

iPhone case model
knuckle duster model

If you don't find anything you like on Thingaverse there's loads more models on 123D Gallery and TurboSquid.

If you've downloaded .STL files you'll need to convert them to .OBJ files before you can edit them (if you have .OBJ files then skip to the next step). After you've found the models you want open each model separately in Netfabb and export as an OBJ file: Part > Export Part > As Wavefront OBJ. Next, we'll combine the models in MeshMixer.

Step 2: Merge With MeshMixer, Make Watertight in Netfabb

Meshmixer (picture 1):
Once you have your .OBJ files, I followed ShadyLogic's steps on how to edit with MeshMixer and was able to quickly import 2 models. Import one model, then import another making sure to "append" the project to have both models in the same environment.

Using the alt+right-click/alt+left-click mouse button(s) I was able to navigate around the MeshMixer environment and line up my models. I placed the palm portion of the knuckleduster inside the iPhone case with the finger openings resting on teh outside edge of the iPhone case.

After the models were lined up I used the 'select' tool to paint the palm of the knuckleduster, then used Edit > Discard (X) to delete the highlighted area. You can merge the two models by selecting one model then Shift+Click the other model (they should both turn white). Then go to Edits > Combine to merge the models into one.

Netfabb (picture 2):
Now we can export the merged model back to NetFabb so we can make it watertight before sending it to print. In Netfabb go to Extras > Repair then find Automatic Repair on the bottom right, then execute the repair. You now have a watertight, custom 3D model to send to the printers. Save the model as an .STL or .OBJ (depending on what the printing service requires.

Step 3: Print

After you've got your .STL or .OBJ file you'll need somewhere to print it. Desktop 3D printing has come to the hobby maker, and the Creality 3D printer is a great way to get into printing at home.

There's companies like shapeways and i.materialize, the pricing will depend on the volume of your model. After submitting your project for printing all you can do it sit back and wait for your model to be shipped to you. When it arrives, tear into the packaging like a kid at Christmas and dig out your model.

Step 4: Insert Phone

There was a fair bit of fiddling to get the phone into the tight-fitting case, but I eventually got it in. My model was printed on white ABS plastic, meaning it was stiff and did not have any 'give' when I tried to get the phone in. I might see if I can have this printed again with a slightly rubberized medium, allowing an easier transfer if I wanted to take my phone out.

You're now ready to take on those mean streets and let all those around you know that you mean business with your knuckleduster iPhone case!