Things you'll need for this:
Cellphone in need of leather case
laser cutter, 3D printer, or a typical inkjet printer
Bolts or clamps
Stitching hole punch
thread and needles
Calipers or dimensions of your phone
Some kind of CAD program
Shears or a very sharp knife
maul or mallet
water resistant finish
Step 1: Get the Four Basic Dimensions
First thing you want to do is get your phones dimensions, focus on the thickness of the phone, from the screen to the back, the width of your phone, the height of your phone, and the radius of the corners of your phone. The radii of your phone are difficult to measure, but if you can get a rough value it should work out just fine.
Step 2: 3D Modeling
Using your favorite 3D modeling software, draft up a model of your phone case. My recommendations for the dimensions are the width should be twice the width of your phone plus twice the thickness of your phone plus .25" to allow for stitching. (2W+2T+.25"=overall width of case) The height dimension should be the height of your phone plus .25" again to allow for stitching. (H+.25"=overall height of case) This is also when you should add in any necessary holes for your the camera on your phone, any flash lights, if your phone has them, a hole for the speaker, and in some cases a fingerprint scanner.
Step 3: Making a Wetform Mold
First you're going to want to decide if you're going to use a 3D printer, laser cutter, or just old fashioned paper and wood to bring your mold to real life. No matter what, you're going to need to create a working model in your cad software. This model will ideally have just enough height and width to allow all four corners to be complete and have suffeceint grip on your phone, about 1/2" in both directions for each corner, in order to reduce wasted leather. If you're going to use wood, simply print out this piece, carve a block of wood to be the same thickness as your phone, and attach this to a wider piece of wood. If you're going to 3D print your mold, you'll need to generate the third dimension of your mold as well as the base that the mold is attached to. If you're laser cutting acrylic or some other cheap material, you will need to layer the material to mimic the thickness of your phone. It doesn't have to be exact but the closer it is the better. Also if you're going to use a laser, I would recommend engraving where the base of your part is going to sit in an effort to make positioning easier.
Step 4: Creating the Clamp for the Mold
For laser cutting and 3d printing you will need to generate the part of the mold I call the clamp. This should have a hole cut in the middle of it to allow the base of the mold to push the leather through. Make sure to leave some clearance for the thickness of the leather. Other than that and ensuring the holes are in the same place as in the mold base, this part is pretty simple.
Step 5: Creating the Mold
This is where you put together all of the preparation. I chose to laser my mold since it's faster and because I enjoy using the laser cutter. I cut out four copies of my phones profile and attached them with some VHB adhesive which I then attached to a base piece of acrylic. I then cut out the clamp portion. Lastly I cut out the outer case portion which I'll be using as a stencil for the leather.
Step 6: Molding the Leather
Now that you have your wet mold it's time to put it to use. For this I recommend some thin leather. Wet said leather, and stretch it over the mold base by hand. Once you have it stretched over the mold, mark holes on the leather, punch those holes, then relay the leather onto the mold. Press the clamp down onto the wet leather and bolt the base to the clamp and allow to dry.
Step 7: Cutting Leather
Using your stencil, transfer the pattern onto your leather using either a pencil or a stainless steel stylus. Once you have the first piece cut out, flip the stencil and repeat the process so you can sandwich the two pieces together. At this stage you should tool the leather if you would like to personalize your case.
Step 8: Stitch Hole Placement
Line up the two sandwich pieces of leather and glue together. Weigh down and allow the adhesive to set. While that dries, take your now dry wet molded leather and cut into four corner pieces. Once you have these punch holes into them to get ready to attach to the rest of the case. Line up your phone with the holes for your camera, speaker, and any other accessories as a guide for the placement of your corners. Hold your phone in place firmly, position the corners, and begin transferring the holes from your corners to the sandwiched pieces.
Step 9: Extra Holes
Some phones have headphone jacks or front facing cameras, and the microphone which may be covered up by the leather corners. Now would be the best time to punch holes for these
Step 10: Stitching
Begin stitching your case together. I first stitched the four corners onto the rest of the case, and then proceeded to stitch the boarder of the rest of the case. Once you finish the stitching back stitch two or three holes and either tie a square knot or burn the thread and press the molten material into the case using a steel tool like the handle of a rivet setter. Do NOT use your hands! Before stitching figure out which pattern you're going to use. I almost exclusively use saddle stitching as it is the most reliable and dependable method.
Step 11: Finishing Your Case
The mark of a true craftsman is their attention to detail. I'm not that great but I put in an effort. Using Gum tragacanth, beeswax, or a combination of both and an edge burnisher go around your case and burnish the edges. This will give your case a nice finished look. After the edges have been finished apply any desired dyes to your case. Once these dyes are dry make sure to apply a finishing coat of protection. I recommend acrylic rosolene, or if you didn't use a dye, neatsfoot oil.
Once you have finished all of the small details your case is done. Enjoy your handy work and the admiration of those who would also want one.