Ok, I'm starting to CAD a design for a woodworking (and maybe light aluminum) router. Work envelope is going to be around 48" x 36" x 7".

When I build stuff, I tend to over-engineer things. So, with this project, I want to make sure I don't do that too much, and spend a ton of money I didn't have to.

So, I looked up specs on THK linear rails/carriages. Even the smallest (15mm rails, 34mm carriages) have a vertical load capacity over 1,000 lbs. Horizontal capacity is over 580 lbs. I'd be using two carriages per rail, so even more distributed load capacity, right?

But the problem is...I *know* that these small rails are going to "look" like they are not strong enough. Should I just trust the specs and go for the cheaper, smaller rails? I mean, there is no way my router is going to see forces anywhere near the rated spec on these rails/carriages.

Same question about aluminum plate. My goal is to build the entire gantry (and z-axis) out of 0.500" stock - and try to use one screw size as much as possible for assembly. I've seen pictures of some of the routers folks here have built, and man some of them have aluminum parts that are 2" or 3" thick! I know some people get materials cheap or free as scrap, so maybe that's the reason.

On some parts (like the stanchion that connects the ball screw to the z-axis plate, and the z-axis sliding plate itself) I know I need thicker than 0.500" aluminum -- but am I okay using it on the rest of my design, as long as I pay attention to span distances? I can't imagine that there'd be much flex in a 0.500" plate of aluminum across a 12" span, right?

Thanks for any guidance you can give me about this topic.

-Chris