Originally Posted by
peteeng
Hi All - To round out the issue of the size of the column in concrete I did the math. If the steel one is 200x200x20mm thick as before, the concrete solid one (or an EG one) has to be 281mm square. This would weigh twice as much as the steel one but be of equal stiffness. To be lighter it would need to be bigger again and hollow. The solid 200x200 has an I=133,333,000mm4 and the steel section is 78,720,000mm4 so the steel is 78.7/133.3= 50% the inertia of the solid concrete yet its 4x stiffer mainly due to the material stiffness delta. OK so moving along to a more detailed design....
As Milli is small its driven by the packaging size of its std components more then the chosen geometry for the parts. This is why the geometry is constrained, I am sizing down not up. Peter
1) It has to be stiff, say 20N/um or better on all axes, if its not stiff then no-one will want one no matter how attractive the price.
2) Cost, it has to be affordable
3) Weight and to a lesser degree size so that it be practical in the home workshop. Benchtop/stand size minimum weight
4) For my purposes it will mill composites and aluminium so a HS spindle such as a GPenny metal maybe the answer
5) My parts tend to be long & high (moulds) so 600x300x400mm envelope maybe good
6) I prefer a fixed table vs a moving table
7) max part weight 50kg (prefer 40kg) for easier transport and manual management
8) may think of something else soon - all good to go for the next 1000 entries...