My solution is to make a 90 degree wood bracket using pine moulding. For a neat finish, this bracket should be as tall as the entire BILLY corner bookcase plus extensions.
To make the bracket, secure the two pieces of wood to each other at 90 degrees using screws.
Then, secure the two BILLY Bookcases to the wood bracket from the back of the bracket into the bookcase. Use wood screws to secure the bracket along the entire height of the bookcases. Be careful to leave a 3/4″ margin in front to allows the doors to open.
When it’s all fixed and in place, add the doors as per IKEA instructions.
I also used the recommended fixing to walls by IKEA for BILLY bookcases. These were bracketed to the wall with the supplied wall brackets. They were fixed with firm anchoring with steel crimped bolt threads into plaster board with 1/2 bolt threads. See picture of tool crimper and plaster fixers used.
How long did it take and what’s the cost?
The cost of materials came up to less than $20AUD, not including the BILLY bookcases.
And it took about 16 hours to do modifications.
What was the hardest part of this hack?
The hardest part of the hack was adjusting the IKEA hinges so that the doors would not jam against one another.