Why the gap between the support/spoil board and beams?
 

I've been wondering why there would be a gap between the spoil and support boards and I found this from Gerald on the shopbot forum http://www.talkshopbot.com/forum/messages/7/4186.html:

"I am only trying to encourage some lateral thinking. For example, if your main work is going to be on 49 x 97 MDF, then 48 x 96 is not relevant. We work metric, and the table of our PRT96 is 2620mm long - again, 96" means nothing to us. A good y=0 line/edge/upstand/gutter/whatever, cut by the SB parallel to its own x-rails, is much more important than a table size. There is no need to cut this reference edge all the way down to the steel bearers.

Plus I would recommend that the table top does not fill the whole space between the x-rails - leave space for clamps and sweeping off sawdust."

Hope this helps anyone else with the same question as to "why".

Thanks,
david