Thanks for the information regarding attachment (apologize I had to send this as a new comment rather than as a reply to your response, as the website keeps telling me to type the two words even though I already did so and only recognized that when I posted this as a new comment). At any rate, I'm in the middle of building one based on what you documented and wasn't sure until now how the attachment to the frame went - I haven't worked with metal much (the welding was a bit of a stretch and new thing for me =) so wasn't aware that metal screws would be able to thread into the square tubing to hold well. I was down to the part of putting the inner bookcase shell into the frame and trying to figure out how to hold it there solidly without having something like bolts that would show (anchors I found at home centers didn't work out very well in my tests in scrap material so I gave up that route). Appreciate the insight and your excellent instructions on what you built as well. Thanks again.