turns out this was discussed recently over at shapeOko forums.
I can’t give you an exact number, because my SO2 has been modded extensively and wouldn’t be representative of a new unit. Maybe someone else can help you with an exact measurement. But it probably won’t be much more than 2 inches - if that…
I recently took the center extrusion out, squared up the frame and cut a piece of 3/4" MDF to fit tightly inside the frame and flush to the top of the frame.Then I ripped a couple 2x4’s down, cut a 3/4" rabbit, cut them to length and slipped those over the frame on the y and x sides and screwed them to my table. There is no way that sucker is gonna move now! I cut some 1/2" MDF for my waste board, if I need more Z height I just remove the top board…
have had a Tormach and a Mechmate. I would say no. Just make sure all pieces are secured and secured to each other. My next machine I am building will have a sub- surface so I can pull a trap door and use a hidden vice. good luck on your future projects would like to see them.