I am going to have to build two tables. My HO layout will go over the top of my son’s O-scale 4x8 (on wheels so he can pull it out). My question is about what material to use for the long span (at least 8’ 6") on my (upper) layout. There won’t be a center vertical support (on the front at least) and I am concerned about sagging. Will steel studs be strong enough to span that gap without sagging or will 2x3’s do the trick as well? Any thoughts? By the way, I have to biuld the tables with this orientation because of space in the room (I know it would be easier to have the lower table pull out from the short (4’) side of the table but then the table will take up too much of the room.)
Well, steel shouldn’t warp or twist like wood would, which would be a plus for such a long span. And if you were concerned about strength, you could always double up the studs or just place them closer together on center (i.e. more studs/joists).
Another option would be to find a piece of 3/16 or 1/4 steel that is long enough and would fit inside the steel stud and bolt it to the stud (the 1/4 thick steel piece runs full length of table, bolted into verticle part of steel stud)… That would add a seriously rigid support… In my first house, someone had remodeled and yanked out a bearing wall and instead of using a real beam, they used 3/16 thick 3x3 steel angle iron, which nearly held up the second floor without sagging 
I’m afraid to ask.
If anyone is out there who has a copy of “How to Build Model Railroad Benchwork” handy, it gives the maximum length of various size lumber without sagging. I’m not sure if a 1x4 would provide that or not. I’m using 1x4s as L-girders with runs longer than 9’, but the attached 1x2 flange adds some rigidity and thus distance capability to that.
I’m goofing off, uh, diligently working today and don’t have my copy of that book handy. [}:)]
I actually have that book (but forgot about it until your post). I will check it when I get home. Thanks very much.
Much of the strength and rigidity of steel stud walls (or a platform, in this case) comes from the sheathing it is faced off with, sheetrock in most cases. Freestanding steel studwork will not be overly strong across such a span but if faced both sides with plywood you’d be able to dance on it without it sagging at all.
I’m sure the steelwork in the MR layout works as it is just great but I’d never want to bump sharply against one of those angled support studs coming off the wall and just slightly crimp it, for fear the entire layout could suddenly loose strength and sag.
CNJ831
I think the correct answer depends on how much weight you will be putting on your layout. If you are using almost exclusively lightweight materials such as foam, a good-quality 2x4 frame should work fine; if you are using much Hydrocal or equivalent; a wood frame would probably sag. A technique that I’ve seen used successfully is a marriage of the two materials: a 2x4 with a THICK piece of aluminium angle screwed to the inside.