Step 1: Supplies
-Small grinding attachment
-Wire wheel attachment
-Sand paper (or sponge)
Not puictured: Image editor (ie: Photoshop, pencil)
SAFETY NOTE: We're going to be using a Dremel tool at higher speeds, and small bits of vinyl will fly everywhere. I thought my normal glasses would be fine for this task, but the high speed debris hitting my eye proved me wrong. Play it safe and use something with full coverage.
Step 2: Create the Stencil
Measure the diameter of your record. Not all 12 inch LPs are created equal. Mine happened to be 29.65 cm
Find a picture and copy it into Photoshop (or some other image editor). Get rid of everything you don't want, and resize it to fit your specific record. Print it out, cut it out, and tape everything together.
My stencil is covered in packing tape on both sides. I'll probably reuse it, so having something laminated (so to speak) will be reusable.
Attach it to the record (I used more packing tape) to keep it in place.