Yes, I agree. I would think just for a 4 x 8 table the gantry tube would be near 6ft. So 7ft or so?
It's called project over kill for a reason.
I've browsed through that thread a few times, some seriously nice metal working! I have wondered how it turned out in the end and if they were happy with the finished result.
I have been thinking about this a bit more. I think the under the table drive could just cause more work for a machine so big. In your shoes I would do dual drives mounted on the sides, and either put the rotary inside the main frame, perhaps with some removable table sections OR come up with a chip deflector to keep from getting debris directly into the ballscrew next to the rotary if you do it like the camaster.
If you use rack and pinion then you don't have to worry so much about debris from the rotary gumming things up IMO.
Servo drives for this?
Also I'd personally use really big tubes to keep the frame design as simple as possible. Do you have an overhead hoist or crane?
That's all I really have to say, unless you make some drawings, then I may say more.
Good luck
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