My step dad Bob is going to call the fab shop on Mon.   I instructed him on what to ask specificaly reguarding a seam support.   At this point the top can be rejected.    I drew out  a steel support system,  because of the dual overhang the drawing depicts a "hip roof "type of welded frame.    Im sorry but this just seems like the  "$hit it & git it " approach.   The material is Corian and we don't do Corian so Im not up to speed on thier requirments.   Im willing to bet there is no seam strip,  I hope im wrong.    Had I known the shop would let my folks do their own install I would have asked for that in the first place but I didn't want to deni a man from making a living or compromizing his warranty. 
size correction   38x62

I suppose that "technically" you'd get good support out of the full substrate even with rabbetted areas for the seam blocking. But "technically" you'd be voiding warranties.

I'll use the metal, thankyewverymuch.

Did you know HiMacs says to avoid MDF.  That solid hardwood, plywood, or steel is better???

Is there really a warranty issue with overhangs and MDF? I thought most of the warranty issues were around cooktops, sinks and inside corners?

I was just surprised to see HiMacs saying avoid MDF in the fabrication of their material.

Have you ever seen a fabrication using solid hardwood only, or steel only?

When I was trained at ISSFA, MDF was the topic of the day.

Posted By Kelsey Crisp on 31 Oct 2009 03:18 PM
Did you know HiMacs says to avoid MDF.  That solid hardwood, plywood, or steel is better???

Kelsey:

Your information is accurate:

"The best substructures for LG HI-MACS countertops are made from multi-ply plywood, solid hardwood lumber, or tubular steel. You want to avoid MDF, Particle or Flake Board. These considerations are not stable and are subject to warpage and expansion with the presence of moisture."

These guys are idiots and do not know of what they speak. Although I've never used Oriented Strand Board a.k.a. Flake Board (they don't even know the real names) as underlayment, all three are much more dimensionally stable than plywood and especially solid hardwood lumber. Don't make me look it up.

Solid hardwood lumber? Are they out of their minds? That stuff grows on trees!!! If it gets a hankerin' to curl, it curls and there ain't a silicone on earth that's going to stop it.

This crap was written by a guy in a suit with several college degrees sitting in an air conditioned office who's never seen the business end of a router, let alone had the financial responsibility for a call-back.

Geesh,

Joe

And Medex is an MDF, but it has a relatively low coefficient of expansion regarding humidity.

Joe, To be fair, particleboard is often referred to as 'flake board', or even 'flake'. At least he didn't say 'chip core', as I have heard elsewhere.

Do you remember color core laminate? I've seen tops fabricated according to instructions warp so bad they tore #8 screws through cabinet face frames. Not a pretty sight. Almost an automatic solid surface sale.

Posted By Andy on 31 Oct 2009 10:14 PM
Is there really a warranty issue with overhangs and MDF? I thought most of the warranty issues were around cooktops, sinks and inside corners?

The imperfection eradication engineer's (repair guy's) answer to this is "that's right". The only real overhang issues we see are when the load capacity has been far exceeded, subtops were not installed or when corbels (or steel bars) were clearly needed and not used.

By the time you have broken a countertop with almost any (>3/4") well secured subtop underneath it, you've worked at it if the support structure is appropriate.