I've been working on the waist moldings and sliding frames the last few weeks. The idea was taken from French bureau plats of the 18th century which is essentially the same time period that I designed this English breakfront. I haven't seen any precedent for this design but it's not an unreasonable idea and it's a good reason to hire me to make a custom piece of furniture. The undulating moldings on the base, waist and cornice definitely slows things down more than I expected. The effect is ultimately nice but each frame takes three times as long than simple rectangular frames. I'll explain the images below.
The waist moldings just placed on the lower section at this point. The frames slide left and right and use the center brace as a stop.
The center brace is dry fit and removable to insert and remove the sliding frames.
The brace has a stub tenon and a half lap joint. This reveals an opening for the tongue on the slides to be inserted or removed.
The tongue for the slide is lined up for removal from the rails.
One of the sliding frames just before glue up. All mortise and tenon joinery.
One of the tongues just before gluing into a mortise on a slide. The grain of the tongue needs to be at a right angle to the slide for added strength.
This image shows how the nicely figured oak slides are cantilevered from long rails that will remain under the upper section of the bookcase.
Corner detail of bookcase with the upper section in place. The slides are not noticeable.
Slide partly extended.
The slides still partly extended will pull out about 20 inches.
Current state of progress. The cornice needs two more layers of molding before it will be completed.