This is a quick and dirty jig I threw together from scraps I salvaged from my local TechShop's "Bin Wall".
Each work area at TechShop has a bin with random supplies for members to search for useful parts to use in their creations.
This jig holds thicker covers at a 30 degree angle for a version of Coptic book binding where the stitching doesn't show on the covers but is all located on the spine.
Step 1: Parts Salvaged and Tools Used
For this jig I used a two foot scrap of wood, some thin plywood, a pin from an old HDA and 8 hex headed Phillips screws.
The tools I used consisted of a miter saw, a belt sander, a drill press and a handheld hex driver.
First I cut off a section of the large piece of wood at a 30 degree angle, placed it on top of the base, drilled a hole through it and partially into the base for the pin (this is just to keep the small part from getting lost while the jig is in storage).
I then cut about 6 inches off the base to be used as the anchor. I remove some of the sharp edges on the belt sander.
Turning all the pieces on their edges, I clamp the anchor to the base, drill some starter holes for the screws through both the plywood and the base/anchor assembly, drive in the screws and repeat on the other side.
Step 2: Final Jig and Action Shot
After the jig is assembled, I clamp my cover into it and place it on the drill press, I set the drill press to only go deep enough to come out the inside of the cover. I found that if you include another piece of plywood (not shown) on the inside cover when drilling, you have less tear-out as the bit comes through.