Limiting unsupported extension on Zaxis.

[Rogue]

I'll start the question by setting out my goals, because context can change every answer!

The majority of stuff I want to do would need the full travel of the table (200mmx200mm planned, might end up larger depending on parts availability) but would not need more than, say 30mm Ztravel (see example 1 in the picture - not to scale but you get the idea).

Occasionally I might want to work on something with very limited Ytravel but might need 120mm Ztravel (see example 2 in the picture).

I'm currently considering a fixed gantry machine where the X/Y is handled by the table, leaving the gantry to deal only with Z. The gantry itself can then be closer to the table and the motor would be supported all, or almost all the way, depending on how the work is held/size of endmills etc.



The vertical grey part represents the horizontal plate of the gantry itself, probably built along similar lines to the one in JAZZCNC's post here: http://www.mycncuk.com/forums/showth...ll=1#post23883 and Jonathan's post just above.

Would this setup (where X is handled by the table) work better than have the X as part of the gantry? I'm leaning towards seperate motor/spindle with belts, so more weight for the Z to handle. I was thinking this design would lend itself to added rigidity? I'm planning to deal with aluminium - mostly thin plate but occasionally larger chunks.

Compared to the other setups I've seen where the Z extends down much further below the gantry, is there an appreciable difference in having the Z travel set up so that as much of the motor is supported as possible?

As always, I appreciate your time, help and input!