walls
The requirement is to hang a bike on 1" dowel mounted on floating shelf bolts. The bolts will go into studs and their length is 2.5". The bike weighs 60lb and will be 10" away from the wall. I think this isn't going to work; it'll just fall. Anyone have any experience of this?
It's basically this product https://www.amazon.co.uk/ZWEIRAD-Sticks-Copenhagen-various-Natural/dp/B01C34NZAM but a DIY version, with bigger screws.
I would drill a small hole through the plaster first to test your theory about how much space you have behind the plaster. Your bit will stop when it hits the chimney, and you can use that to judge how much room you have.
If you have enough room, I would go with a toggle bolt style fastener. If not, then you might need to use a masonry bit and drill into the chimney. From there you can use a long tapcon screw to go through the plaster and into the chimney brick.
A "C" (or perhaps "[" is better) shaped shelf could sit under and behind the couch, keeping it no more than an inch or two (even less if it was metal plate for the section behind the top edge of the couch) off the wall, and holding the projector above the couch without needing any attachment into the walls.
Not exactly what I'm thinking of (not having much luck thinking of the right search terms to find what I am thinking of), but the general idea - legs that can slip under the couch, standards, a shelf.
Best Answer
To properly analyze this you'd need a good drawing of the forces acting on the system (a free-body diagram). Without seeing that, and without knowing the materials you intend to use (ex. what grade fasteners, what size fasteners, torque values, what type of wood dowels, how the bolts secure the dowels to the stud, etc.) it's incredibly difficult to say whether or not it will work.
My biggest concern is not that the bolts will fail, but that the wood dowel will break in tension. I'd be worried about the area under the fastener head. If you can provide a drawing, I'll try to edit this answer to be more specific.