Let's say I'm designing a table surface which has to be stiff, rigid, but at the same time, not too heavy. It is rectangular in shape and ratio of length:width is quite large. It is only supported on both ends of its length. If I use a 50 mm slab of gray cast iron for the surface of the table, during maximum loading the table will bend and the Z-axis displacement at the center would be 0.04 mm. This table will be used as a machining table, and the maximum tolerance of the workpiece will be 0.005 in (0.127 mm), so I think the 0.04 mm deflection of the table is already good because it will give room for tolerance from other component of the machine, such as cutting tools, spindle, etc. Problem is, with 50 mm steel slab, the maximum weight criterion is exceeded. The whole table is designed to be able to tilt on A-axis (it's a trunnion table), driven by a motor. The heavier the table is, the bigger and exponentially more expensive the motor would be. I have to reduce the weight of this structure, but I have to keep the stiffness.
What if instead a simple flat 50 mm slab I make it like 20 mm slab with extra stiffener profile on its underside? Like honeycomb pattern, or any other stiffener configuration. which is possible because it's a cast iron anyway, just have to create the mould.. by doing that I could reduce the weight by almost 40kg
The question is: Is it theoretically possible? 50 mm slab gives 0.04 mm bending displacement, now I want to make it like 20 mm slab plus some stiffener to reduce weight, but I would like to keep same performance with 0.04 mm maximum displacement. The maximum load is 1200 N, concentrated in small area in the middle of the table.
EDIT: previously I wrote the requirement as 0.005 mm deflection, but it is actually 0.005 in (0.127 mm). However, this +- 0.127 mm figure is basically the machining tolerance of the workpiece that will be made on top of this table, so I guess the tolerance of table itself should be much lower than that, I don't know the exact number yet but it just won't go as low as 0.005 mm that's probably too extreme. I'm still in the early stage of the design so a lot of design requirements is still open to revision..