Thanks, Trebruchet. How far out toward the edge does the tube steel go and how close together do you space it?

I used 3/8" x 2.5" flat metal bars that went down the full width of the countertop (including overhang), spaced every 24". The bars were routed into the plywood support (I used 2cm quartz) so that the countertop laid flat on top of the base.

lori,

Click on the link below. It will take you to the Federal Brace Website. They have lots of options for invisible counter support.

Here is a link that might be useful: Federal Brace

Thanks, Mark and Calumin. I don't want to pretend to tell the fabricators how to do their job, I just like to be informed about options before I'm asked to make decisions. That Federal Brace site is fun-- I could find all sorts of fun things there as well as what I was looking for!

You might also want to check out Centerline Brackets. They are 1/2" thick, so they are far stiffer than the 1/4" ones that you typically see. Plus, their pricing seems more reasonable.

Here is a link that might be useful: Centerline Brackets

"How far out toward the edge does the tube steel go and how close together do you space it?"

2" from the edge or so; 16" on center give or take.

Our island has an 18" overhang for seating on 3 sides. Our stone fabricators built a steel frame that supports the entire counter, instead of a plywood subtop.

Here is a link that might be useful: steel frame

The steel frame seems like an over engineered solution. That's fine to do, but I'm sure that it wasn't cheap.

If you can find a metal service shop in your area, they should stock steel bars and cut to order - that is probably the cheapest approach. I think I paid $45 for three 34" bars, cut from a single 10' strip.

From there, the GC should be able to deal with the rest.

IIRC, the steel frame was about $600. It might be over-engineered for a 12" overhang, but not for our 18" overhang with quartzite. With 2 little ones, we weren't taking any chances with a large stone overhang not being properly supported.