a solution for gaining 10 cm more space on the z axis
 

after long discussion on which would be the best for gaining space with the minimal reduction of the rigidity of the structure, we wondered whether we should lower the working plane or build on top of the main beams.

we decided ourselves to lower the working plane by adding a 100x50x6mm beam right under the main beams, welded also on the legs and cross pieces.

this allowed to reinforce the "weak point" of the structure, which we identified in the connection between the main beams and the legs, allowing some degree of sideways oscillation.

still, lowering the working plane also meant reducing the efficacy of the cross pieces on the short sides, as they would be working on closer parallels.

therefore we added diagonals also on the central part of the machine and one more horizontal element for connecting them.

I am wondering whether we should also consider the possibility of adding two more diagonals on the second horizontal element of the working plane, connected to the same horizontal element as the existing ones.
this would greatly increase the rigidity of the endings of the machine...

do you think it would be useful/necessary? if so, I'd rather do it right now than wait until the machine will be working...

I think your added flex is still going to be more in the z axis with the extended reach.

I agree with Heath.

We discussed with Antonio the problem of adding flex to the Z axis ... the kind of work the mostly do is 3D with styrofoam .... considering the height of material is 100 mm ... you need a very long ball mill +- 120 mm ... +30 mm of mdf ... + sacrifical board ... the classic 200-250 mm it's not enough, so they choose to have a "mamba" z axis of 350 mm capability.
The question here is ... (which I think is a general interest question), is understanding which would be the best solution to follow to have the best base table for a 350mm z axis capability. (I already did some research on the forum and the Antonio solution seems to my "dummies" eyes a good one)
The added flex to the Z axis is well understood :-)

Without a redesign of the Z axis, I think you are working with the best possible solution.

thanks for your opinions, thanks Sergio.

we've already been working our machine almost everyday for approx six months with the same distance. regarding the Z axis flex we did not find we were having a problem, with the soft materials we were using.
but the base seemed too flexible (it was not a proper MM base but something built in Aluminum) and shaky, remarkably so in the direction perpendicular to the long sides.

now we've built the structure you've seen, in order to be safe with shakiness and out of control movements on X and Y.
but it still has some movement in the same direction(perpendicular to X): a strong shaking impulse given with both hands (maybe some 60 kg?) is able to provoke a lateral movement of the main beams of approx 2 mm. it is an impulse, something you would not see so easily, so I applied a caliper to a fixed structure, put it in contact with the rail and gave the blow.

so I wonder: I thought the solution for extending the space in the Z direction could be good (it should not increase flex of the main structure)... should we still work on the rigidity of the base as we are now in the moment in which it can be done?

You can if you wish, Remember you are making a frame, not a cast base. There will always be a little movement because of that. I am not sure it would be necessary but you need to be happy with the end result.

thanks Blackburn.
we'll leave it as it is then, I'll let you know if this should reveal to be an inconvenience. but your description seems to imply that some oscillation cannot be avoided, as I had started assuming.

I giggle like little girl when I read 1/2 way through the title "a solution for gaining 10 cm more..... " :P

is that the reason why you chose to build a blue "drilling machine"? :P