kjmillig

I'm copying this over from another thread:
I enjoy building all kinds of stuff, so when I started looking at cartop racks, I decided to build one. Now I'm almost ready to mount my 2x4 cartop bike rack. The rail is a 2x4x54" with a 7 1/2" crosspiece attached to one end with a lap joint. I then cut a channel in from the end opposite the crosspiece up 22", 3/4" deep, and 1 1/2" wide with a dato blade, smoothed the channel with a straight router bit, the half-rounded the edges with a router. I've mounted a Saris fork mount to the crosspiece after sanding and a double coat of flat black exterior paint. 3" stainless u-bolts will mount it to my factory luggage rack. I'll only be carrying one bike (mine), so I won't overload the factory rack.
I'll get some pics up as soon as I can. Has anyone else here built a rack before, cartop, hitch mount, etc?

Retro Grouch 

So how does the factory rack attach to the car? I'm thinking the issue might be lift rather than weight capacity.

kjmillig

Channels are screwed to the roof. Crossmembers have a thumbscrew going into a square nut in the channel. Very typical factory installation. I made sure the channels were screwed, not just glued on.

Retro Grouch 

Screwed into sheetmetal. That's exactly what I'd be concerned about. Keep in mind that I'm a mechanic - not an engineer so I don't honestly know it that's going to be adequate or not.