I have not found a full 1 inch thick sheet of shelving material.   I believe 3/4 inch is the max.  Now if you go look at counter tops or the custom shops for them you may find some.

As far as I know, "Melamine" is just a surface that is put onto particle board.  Particle board isn't particularly rigid (as Mike mentions), and it tends to take a set if it's not stored flat.  The last thing you want is a chunk that's thick enough so that you can't shim it into alignment!

Mike's a retired machinist and builds good planes -- if he says to do something to achieve precision, you should do it unless you have really good reasons for doing otherwise.

  Hello Dick
                      I made mine out of 3/4 x 12.5 x 48 inch plywood and to keep it straight I bolted two rails of C section 1 1/4 x 1/8 inch aluminum extrusion  also added some oak rails under it that way the aluminum is not scratching where I place it. I use it for wings and fuselage building. I always check it before I start building on it.Here are pics.
                                                                                                               Juan

Or you could just glue 1/2" to the back of your melanin to make up the dimension.

In the auto industry we wasted millions of dollars over many decade trying to precision-level everything.  Now they just slop it in within an inch and tweak it with a laser level.  Maybe in the near future modelers will also quit leveling the world and start lasering the critical elements.

Hi Dick,

I, too, am setting up a CLC jig.  I found a piece of 3/4" shelving board that sighted as straight as I could find.  It is 6' long and I am going to cut off a foot leaving it 60".  That will be fine for any wing I am building.

BIG Bear
RNMM/AMM

because I found a piece of 25" x 66" granite cheap.

There's often bits and bobs of granite on Craigslist fairly cheap.  It's not 4" thick super-flat machinist-quality, but it's probably better than what a lot of folks could come up with otherwise.

Tonight I went to Home Depot and bought a 4X8 sheet of 1/2" MDF, which is the stuff they glue melamine on to make shelves.  It is smooth and warp free.

I had it cut to provide two pieces 20"X60" which is the size of my bench top.  Tomorrow, I will glue and screw them together to make a laminated board 20"X60".  I will build this on my bench which has a glass top that has been flattened and leveled as needed by using playing cards.  Once the glue is set, I will lay out the grid for the CLC jig components and drill holes for the 6MM threaded inserts that will follow.  The jigs will be mounted with M6 machine screws, 25mm long.  The threaded holes should never wear out.  It is likely that some will never be used, but I can't think of anything more frustrating than to have to drill new jig holes for every new wing or fuselage.

I am excited about this project and plan to take pix and do a small write-up covering the build.