ES> I would think it needs to be a sturdy construction (so the ES> gaps aren't moving in relation to the disc) so I probably ES> want to build it on a steel frame. Bonded hardwood or marine grade 1" plywood is plenty sturdy to handle this gap project. The various components can be bolted down with carriage bolts for a nice sturdy and tight assembly. Richard Quick ... If all else fails... Throw another megavolt across it! ___ Blue Wave/QWK v2.12