Stable wood surface?

I'm building a hot-wire foam cutter, and want to use a wooden mount/base board of some type, about 5 feet by 2 feet.
What's the most dimensionally-stable material to use? MDF, OSB, ply, chipboard, something else?
Thanks,
-- Peter Fairbrother

Peter Fairbrother wrote:
  Quoted Text Here  
I'd suggest moisture resistant MDF - the green one Use a couple of stiffners along the 5 foot dimension. Seal with varnish.
Bob

Peter Fairbrother heeft ons zojuist aangekondigd :
  Quoted Text Here  
I would prefer exterior 18mm plywood. I used what I had, 18mm chipboard as base, MDF for the stand and wood for the arm. Just make sure the wire is, or can easily be set square in 2D. A parallel guide and some holes for cutting circles make it work easy. Dirk

Peter Fairbrother wrote:
  Quoted Text Here  
Don't know what your budget is but I have been considering Jabroc for the likes of metal spinning formers. I'm pissed off with maple and other woods changing size with humidity and the Jabroc is supposed to be very stable . I want to find something that is easier to form than metal but is stable, a number of current spinning formers are in steel or aluminium.
UK dist for the stuff is http://www.permalideho.co.uk/hydu.html

On Sun, 26 Apr 2009 20:17:18 +0100, Peter Fairbrother
  Quoted Text Here  
I made a simple one for a single job about 3 weeks ago - 22mm MDF about 16 in long with the wire 2in above the surface (to slice some polystyrene packing pieces). It had a pretty average sort of spring tensioner on the wire. I now have a banana shaped baseboard where the MDF has bent.
By the way if you want some resistance wire I've got about half a kilometre of the stuff.

Peter Fairbrother wrote:
  Quoted Text Here  
carton making formes (for cutting cornflake boxes from sheets of cardboard)are made from 18-24mm cabinet grade plyboard (the stuff with 13+ layers which are about 1.5mm thick each) - it is INCREDIBLY stable - formes are usually required to a tolerance of about .2mm - which might not sound much to an engineering group, but it's f*ing close for wood.
It's available in 8x4 sheets - might be about 60! quid+ per sheet.
If you have any carton printing companies in your area, you *might* be able to cadge an offcut big enough.

  Quoted Text Here  
E-mail me Peter. I may be able to help depending on location.

For ecomomy, can I suggest a visit to your local IKEA. They do 'spares' of doors and shelves, basically bits left over, usually £1 or £2 depending on size.
Various thicknesses and finishes, usually very flat and nicely smooth finish on one side (often holes on the other though).
MH