[dingo117]

Hello again all. so i was thinking of ways to decrease the deflection of structures for the various axis in a cnc machine other than just piling on more material and preloading came to mind, attached is a picture of my idea roughly and the test setup. the idea is to use a threaded rod and nuts on either end to apply a crushing pressure on the tubes long axis and hence preload the walls to increase its tension. now i did a basic test with what i had on hand last night but the results are not overly conclusive since the threaded rod i had was super soft and nasty so it stripped the threads and the tube section i have is not very wide in diameter so i dont think it would benefit much but as i was tightening the nut on the thread the dial was slowly creeping up so it looked like it was taking away some deflection.

my main question is would this if applied on the right scale say a 1000mm long tube 300x300mm say 4mm wall thickness and a few internal braces using a 20mm or so high tensile rod to apply as much force along its length via thick end plates significantly decrease deflection in the tube? also any idea if this could be simulated in fusion 360
also side effects of doing this, would it make the part slowly warp over time or some other effect i may not know about?

[peteeng]

Hi Dingo - No, sorry does not change the global stiffness. May as well choose the correct size member to begin with. Light structures can be preloaded to gain stiffness but usually only in one direction eg a bridge against gravity, a bowsprit against a sail load. But on a machine that has to take load in multiple directions it's not a useful strategy. Yes, you can simulate this in FE systems not sure if you can do it in Fusion 360. I expect you can, just place the load on the ends and the service load at the tool...But beware of false results as F360 is a linear solver and if the structure is light and behaves in a non linear manner, which light preloaded structures can do then the result will be wrong and you can't tell if it's right or wrong. F360 solver is for stiff structures that behave linearly...Peter

look up the rules of superposition and load sequencing linear vs non-linear