Help making flat jointer beds

[Greg Woloshyn]

I'm working on the Matthias Wandel 12" jointer and it's coming along great, but I've ran into a problem trying to make flat infeed/outfeed tables. His plans specify Baltic birch plywood, but the last two sheets I tried to use were not flat. Most recently I tried making sort of a mini torsion box out of MDF, and since I only have a 1.75" thickness, this didn't stay flat either. Wondering if anyone can give me some other options for material to use.. it doesn't seem like anything I buy will be flat enough to use for this.

[Jamie Buxton]

How 'bout glass? Residential shower enclosures are made from 1/2" glass. Commercial doors too. The cost isn't horrible. It seems darn flat. And in 1/2" thickness it is very tough. To damage it, you'd have to drop a hammer on it from quite a few feet above. I don't think you could break it by hitting it with wood.

[David Falkner]

Or Corian or Granite or similar...