quote:

Originally posted by kal72:
Thanks!
I planned to install the plywood on the INSIDE of the cabinet as oppposed to the outside, so I wouldn't be covering up the factory-finished side panels. The cabinet has full width drawers so the plywood side panel is hardly visible but with the drawers I can't fit 3/4" ply on the inside without interfering with their operation. I could get 1/2" ply in there instead of the 3/8". Better perhaps?

(A.)The 3/4" ply would be a base for the granite on top of your cabinet frame. There is no difficulty in hiding the plywood edge. In fact you could stop it short on the edges say 3/4"-1" to create a reveal under the edge of the granite. If that is unexceptable then a minor set back could be made to make the plywood trim flush with the edge of the granite. The first option would be my choice for the following reason. When wiping the counter top down or in the case of an accidental spill it would not run into the gap(minor) between the trim and the granite. The 3/4" ply would also help distribute the load uniformly over the base.

I also re-read your response, and I am not clear what you are saying about the flat bar?
>"I would run the steel from side to side rather than just the 12" space as you are planning"
Are you suggesting running (a third) flatbar across the L brackets? Or are you suggesting running flatbar perpendicular to the direction I show in my picture?

(A.)No the flatbar would be embeded into a recess of the ply. The longer pieces could be placed on the bottom side and actually rest on your cabinet base. The pieces going the narrow way from side to side could be embedded in the plywood top and aid in supporting the granite in addition to the ply. This would eliminate the need for the "L" brackets.

With "beefed" up side edges, is there any need to put plywod ontop of the cabinet? Structurally, the cab sides will take all the load and I don't particularly want to raise the height of the island particularly since the edge of any plywood would be visible (particularly) on the side that has no overhang

(A.)With the ply you would be uniform heigth. An island unlike base wall cabinets is not sitting directly next to the other cabinets and a minor 3/4" will not be noticed.

quote:

Originally posted by kal72:
Thanks for the patience and all the responses. I really havent done anything like this before so I appreciate you explaining everything so well.

Plywood it is! Since I was planning on spending over $100 on two L brackets that are no longer required (http://www.federalbrace.com/Freedom_Hidden_Countertop_Brackets_ppsqo_VHV22927YTW_VHV119YTW_VHV6YTW_VHV22927YTW.aspx), I think I will put a few steel flatbars in routed channels in the plywood (got a quote from a metal fab shop -indeed much cheaper tha big box!

Again - No harm in doing this (except spending extra money) but for the dimensions and overhangs you have for this project the 3/4" plywood will provide more than enough support.

If I was concerned about the extra 3/4" of height of the counter top, in theory I imagine I could take 3/4 inch off the bottom of the cabinet base. Does anyone ever do that?

I would not cut off the bottom. The lower by 3/4" kick height will be more noticeable than the extra 3/4" height of the cabinet

My cabinet is a painted antique white, I need to match the color and paint the back plywood panel and some base moulding, so I will paint the edge of the subtop and set it back 2-3 inches from the granite edge. On the front edge (where the granite overhang is only 1") the subtop edge will be more visible so thats where it would be good to use the banding, so that you dont see the end grain of the plywood. I assume I can install this banding after the fact if I dont like the look of the painted edge?

You can avoid all the edge issues as well as the extra height issue if you cut down three sides of the cabinet by 3/4". Leave the cabinet face untouched. Your 3/4" plywood will then sit directly on the cut-down parts of the sides and back of the cabinet while the front of the plywood will be an insert that butts up to the back side of the cabinet face. From the front with the small 1" overhang, there will be no plywood to see while the sides and back of the plywood is set back several inches from the edge so it will be less noticeable.

Should I route or bevel the 3 seating area edges of the plywood subtop so its smooth against the thighs? (yes I just said , "smooth against the thighs" in a DIY discussion board). I guess this would prevent me from using the edge banding on those sides unless the edge banding can attach to a slightly routed edge. I figure I could round the corners a bit too, even though the granite is "square".

The banding can handle a curve but it will need to be about a 6" radius. You cannot install the banding on a routed edge - it must be a flat surface. Since you are painting, you can also skip the banding and just fill and sand the plywood edges to get them smooth and hide the plys. I'd still go with the banding though - it's a cool product that is easy to use and give excellent results.

Any finishing tips appreciated!

The granite top is remarkably strong. AS you noted in your original post, a 12" unsupported overhang is right on the edge of being acceptable. Even if you run your plywood support back from the granite edge by 6" there will be more than enough support to keep the granite from breaking. The further back from the edge that you put the plywood means the less visible the plywood is.