Combination of BB Plywood and MDF/HPL for Router Table Top

Hey all,
I’ve seen a number of arguments against Plywood for a router table top and a number of arguments for an MDF/HPL covered top. Typically, it seems that most folks double up on pieces of 3/4” MDF to make a 1-1/2” thick top and then cover in HPL. I’ve a a couple of reports that even the 1-1/2” solution would sag over time if a 3-1/2 HP (aka heavy) router motor is used.
My question is this…has anyone done a combination of 3/4” BB Plywood on the bottom and 3/4” MDF on the top (still covered with HPL) to create a more stable (but still flat) router table top? If so, pros and cons to that idea?
Thanks in advance for the assistance.

For my latest work bench I wanted to have a longer span without supporting ribs. My previous bench was 4 layers of MDF with adequate support. This time around I used 2 layers of 3/4" BB ply laminated for strength and sag resistance. this was then laminated to two 3/4" pieces of MDF for a dead flat surface. You would want your MDF on top for the same reason. I have MDF work surfaces that were flooded with BLO, allowed to fully cure and then waxed that have seen service for a decade with minimal wear so the HPL is up to you. Use a laminate on both sides, of course. I do not run rough material over the router table so even the thin melamine on my Rockler top is wear free after many years of use.

Beam stiffness is proportionate to thickness, all other things being equal (well, distance from the axial centerline to the skin, anyway.) Load is carried by the skins. Core doesn't really matter.

i'd think about a composite panel for a router table top. Use something like 2-inch high density foam, like blue board as the core. Epoxy and vacuum bag, say 1/2 Baltic birch (or maybe 5mm or 7mm marine ply if you're feeling speedy) as skins, top and bottom. Or build a torsion box similarly. Probably want hardwood blocking where the router plate/lift goes to support it.

Finish with Formica, top and bottom (balanced construction). The skins and the hundreds of square inches of epoxy glueline take and distribute the load. Unlikely to sag over time.

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Originally Posted by Nicholas Carey

Beam stiffness is proportionate to thickness, all other things being equal (well, distance from the axial centerline to the skin, anyway.) Load is carried by the skins.

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It's actually proportional to the CUBE of thickness. A beam 2x as thick is 8x as strong.

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Originally Posted by Bert McMahan

It's actually proportional to the CUBE of thickness. A beam 2x as thick is 8x as strong.

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Didn't say "strong". I said "stiffness". Two different things.

Quote:

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Originally Posted by Nicholas Carey

Didn't say "strong". I said "stiffness". Two different things.

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They are two different things, but they're both proportional to the cube of thickness. They're both functions of the moment of inertia, which has an h^3 term in it. A beam 2x as thick is both 8x as stiff and can carry 8x the load before failure.

I have a couple pieces, including my router table top (believe it or not!) that is MDF with Shellac. Shellac seems to soak into the surface and dries to a pretty decent hard surface. Glens combination with the bb seems quite functional imo.

I've made several router tops over the years. I've used both ply and MDF. IMO one layer of ply will not give any advantage.

The key is to laminate both sides. Be sure to use the thicker countertop type HPL.

That said, I would still build a base that will adequately support the top. If you're building a router base with drawers, etc, this will take care of itself.