I've been making these cases for a couple years now for friends. They're very simple yet highly functional and not hard to carve. I like how the iPod's menus show clear through the closed case.
They fit 5th generation, 30 gigabyte Video, and 6th generation, 80 & 120 gigabyte Classic iPods.
Step 1: Materials
1. First of all you will need to find a solid discarded cassette case of the correct dimensions. Most cassette cases of the style pictured fit ipods well with minimal extra room, however some are not quite tall enough so be sure your ipod's hold switch fits snug when choosing a case. As for the extra space in depth and width, we will return to that in the 6th step.
2. I use a Dremel with a tapered sanding bit to carve my cases. You need this bit specifically so that you can drill, cut and polish your case. In the past, I have used a soldering iron to melt the plastic but I wouldn't recommend it.
3. Your iPod video or classic for reference
4. Needle nose pliers
6. A good rag for catching shards and fillings of the cassette case. I've found hand towels to be most effective.
Step 2: Removal of Cassette Case's Unnecessary Plastic Structures
First, carefully separate your cassette case into its two parts (the joint between the two is the most sensitive part of these cases).
Then, Use your pliers to bend and break out the structures on the black half of the case which ordinarily brace cassettes. Leave the structures hugging the side wall since they can be used to brace your iPod
Next, use your Dremel to sand down the broken edges. Use your fingers to test smoothness, iPods scratch easily.
Step 3: Marking the Case
Use your pencil to mark where you will be cutting and drilling away plastic for the click wheel, the headphone jack and the USB connector. You basically have to estimate these with the iPod inside as a guide keeping in mind that the plastic bits surrounding the headphone plug and the USB plug are wider than the headphone jack and USB ports themselves.
Do mark the headphone jack for cutting to the edge (so that you can open your case while using it) but do not do the same for the USB connector. I've found that this significantly reduces the strength of the case.
Step 4: Carving
With the case's two parts joined, drill through the edge of the black plastic and begin to cut just inside your marked outline of the click wheel. Keep the two parts of your case together so that the edge between the parts is smooth and your circle is accurate. Use long, steady motions with the Dremel at a higher speed to avoid nicks. Hold off polishing the edge for now, just be sure that the hole is wide enough so that your thumb has room to use the click wheel. If you go wider by accident just make it circular again, extra room is almost better.
By the way, bits of plastic may melt and form on your Dremel bit (in the long term damaging the bit slightly). For now, I would suggest using a strong Exacto knife to force these loose.
Next, separate the two parts and drill your headphone hole from the edge of the plastic.
To cut the hole for the USB connector, drill straight into the case and then carve the length of the plug. It is important that you use your drill bit's taper to cut the correct width.
Then, put the two parts back together again to carve room for the USB connector in the clear plastic structure next to the hole in the black plastic you've just made.
Be sure all the inside edges are smooth and then place your iPod back inside to test your holes. Plug in your headphones and USB connector and be sure that your click wheel circle is wide enough. Go back and make any alterations if necessary.
Step 5: Polishing
The last step is polishing the click wheel circle so that your finger isn't cut while using your iPod.
Sand in steady long arcs at different angles around the edge. Go back and be sure that the inside edge is not sharp either.
Test once again with your iPod inside and your finished! ...Unless you want to do something about the extra space your ipod has, then check out the optional step.
Step 6: Optional: Cushion Your IPod
For this you will need an old sponge (preferably one that has firmed up a bit) and, if you want to make it look pro, some double stick tape and scrap paper you've drawn or printed graphics on.
So first, cut your sponge to fit the dimensions of the extra space behind your ipod in the case with either a swiss army knife or an Exacto knife (scissors could probably even work). This is basically trial and error since I can't tell you how much room you'll have.
Next use strong double stick tape (I like carpeting tape) with your printed or drawn on paper to cover the sponge. I also used a black paint marker to cover the top and bottom edge which weren't covered by paper.
You can also try cutting a thin rectangular piece to pad the extra width room in the case. This helps to keep the case shut in addition to padding the case.