Speaker To-Dirt wrote: > > >> Cast Iron is easy to machine, but a bit messy, black dust >> flying all >> over. I don't understand your reference to Al and >> gear cutting loads. >> > > I meant I would not trust the structure of the 4th stage being made from > Al. Al creeps, thus never really returns to it's orig shape when placed under > load. If I have to make my own 4th stage, I'm deciding which material to use. > I can get steel, but I was told to avoid steel as a machine tool body because > it's easy to establish acoustic standing waves in that material while iron > damps them out. Which was the reason I understood machine tools are made from > iron. > Small steel structures are usually fine. No question that large machine structures should be made of cast iron, as it does provide a good bit of damping. Heavy structures won't vibrate much under reasonable loads. You can calculate the deflection of a particular structure with fairly simple formulas. Cast Iron also creeps under load, but generally that is a VERY slow process, and it takes years to measure the effect. Probably the larger effect is simple thermal expansion, aluminum is about 6 X greater than steel.
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