After finally decided my idea for a cheap overhead guard wasn't doing any good in my head, I spent a few hours working on it the last couple days.
The idea is pretty simple. Usually these type of guards are a metal frame with DC hose attached. My shop is in the basement so the ceiling is fairly low, so I figured I could drop down with a telescoping plywood box that would be both the structure and the DC duct in one.
The construction is rabbets on 1/2" baltic birch ply, glued and screwed. I made my own T slot on the inner box by running a groove down the center and then a shallower widder groove, then gluing in strips on both sides.
I was expecting to have to use some diagonal bracing, but the pocket screws, all 8 of em, are enough to keep the upper section totally rigid.
There is some movement of the bottom section when fully extended, about 1/4" front to back, not much side to side. Little bit of assembly error I think. I have to bring it up all the way to the height in the first picture to remove the slop. An inch below that and all the slop is there, there and above it's gone. So something is off. There's about 8" of overlap between the sections at full extension. I think adding a second knob 5-6" above the first would take care of it.
I haven't gotten any Lexan for the actual guard yet, I wanted to make sure the rest was going to work first. Not bad for about $15 spent so far though.
-Leuf