raceway build for channel letters

IMO you would be better off buying pre built. They are thick with removable cap on top. I know it seems easier sometimes to save money and do yourself. HOWEVER if you do it yourself I would use .063 aluminum with 1" aluminum square framing

 

https://www.easternmetal.com/signage_extrusions-raceways_and_wireways.html

 

you can pretty much build them the same way they come as extruded, see any manufacturer's documentation of the profile as an example.... extruded just saves you labor & is structurally-sound to hold the weight of itself, and the lettering, and the power/wiring, while you have the service cap removed.

BUT

if you're gonna bend your own metal, by all means, but just design it so it fulfills the above requirements...which means you'll have to beef-it-up with gussets & angle iron, since you'll most likely be bending it out of .063-.090 aluminum that will not hold its shape for long when you remove the cap.

that being said, we have an automatic metal brake with 3", 5", 7", 9" profiles designed & programmed into it and can handle making them out of 1/8" alum....and yet, we STILL buy the extrusions to save countless hours of manufacturing on most projects.

 

I'm going to assume that you just don't want to spend the cash for a full length of the raceway extrusions for just three letters. I don't blame you. Depending on the size of the letters, you can easily build a raceway out of sheet aluminum, anywhere from .040 on up, assuming you are familiar with sheet metal work. I've made countless raceways from .040 aluminum but those always had a welded internal frame (steel or aluminum angle depending on how long ago). I now would use aluminum angle for the framing. Knowing the size of the letters would be helpful.

If you don't usually do sheet metal work, I'd suggest finding a local sign company (or even sheet metal shop) to make the raceway for you.

 

If building yourself, you can make a 4 sided frame out of 2" angle, mount that to the wall. Then fold up 063 just over that size, mount the letters to that, then slip that over the frame on the wall. There are only a couple of issues to deal with.
Wiring. You have to make the connection before final assembly on the wall, which can be tricky depending on how big the letters are.
Service. You'll have to remove the whole damn thing just to replace a power supply or check electrical.
Structural support. If the letters are over 24", then you'll probably want to frame the 063 up instead, then mount 90's (4" lengths of 2"x2" aluminum angle) to the wall and screw through the angle frame into the 90. I don't like this as much because the sign starts to weigh more...

 

What is the size of the letters overall going on this raceway?

 

the "raceway" in the picture you posted....is just a box. an aluminum pan, that caps onto either another aluminum pan or some aluminum angle mounted to the wall.

 

It should work well for something that short. Once letters get too tall, over 24" or so, the raceway install gets a little trickier. Make sure you get the extra parts, end caps, tray for power supplies, and leave enough slack to pull the power supply tray out without getting stuck.
UL should be happy to certify this.