... I did have a few questions (if they're not trade secrets) :
What is the glue / hardener that you used for laminating the ply pieces? Obviously the vacuum is a huge help on top of the clamps for bonding it all tightly.
And I was looking at the flattening process with the router - are there shims under the jig where it rests on the outer edge? I can't quite get my head around making such a jig. Does it rest on the edges of the unfinished side cutting low on the other, then you flip it at the end and raise the bit to keep the same depth of cut?
Anyhow - would love to hear any ideas.
Cheers, Antony.
I would tell you, but then I'd have to...
I used Epoxy (West System), my favorite adhesive for just about anything. I used it only in the top layer, the pieces on edge, the other three layers I trusted to polyurethane glue (easy, quick, and I used screws as clamps, which I took out after cure). No filler was used in the mix, but I did mix a batch of pookie to fill any little voids in the the plywood after the fact. My router sled was a crude bridge, using a 1" bit, the biggest one I had. Time consuming, but effective. I let the bridge sit 1/32" above the rails on the edge and hoped the weight of the router would give me the hint of a concavity in the center of the bench, and it seemed to work (I don't like perfectly flat, and a concavity means things and spills will travel toward the center of the bench.) Plus it is easier to be not perfect.
One thing I didn't plan on was, I couldn't remove the mill marks left by router due to the epoxy and pookie penetrating the end grain, no amount of sanding would work, short of a widebelt and flattening it, but the look was unexpected chic and cool.
The bench looks much less pretty than it did when I made it four years ago, but it is like hitting on an anvil, and has proved a joy to work on. And the ply on ply sandwich is very, very stable in terms of any (or lack there of) wood movement. Though my dovetail pins get a bit more pronounced in the summer.
Good luck with yours.
s