I don't really know how big a deviation from circular is needed, but I'd guess that it isn't much, and isn't visible.
Magnetostrictive actuators generate very high force levels, so one can use levers to trade force for stroke. The length of a Terfenol-D rod changes by about one part per thousand as one goes from zero to 2,000 gauss field.
Joe Gwinn
Ah, right. I was thinking of a lathe that can turn parts that are noticeably elliptical to the naked eye. I imagine it's simpler to design a machine if the workpiece only needs to be slightly elliptical.
Chris
Typical ovality runs around 0.010 to 0.040 inches, depending upon the piston size and purpose. It can be more or less. It could be enough to see, if you took two identical pistons and laid them side-by-side on a surface plate, and oriented them 90 deg. to each other in rotation.
This is for modern cast pistons. Forged pistons are made with an alloy that has a significantly higher coefficient of thermal expansion. You might want to check on diesel engine pistons to see what their range is.
I haven't looked, but I expect that you'll find good information about them at the SAE's website. If you're Googling, look for "cam-ground pistons."
Hard to see then. Not quite beer barrel proportions.
Found a good link here:
Best wishes,
Chris
That's good. Remember, as I mentioned with the Ford pistons, the latest and greatest can have several different profiles from crown to skirt.
I only wish the *real* expert here was around. He's an engineer with a piston company you would recognize, but which I'm sworn not to name. He knows all the subleties, including ones he can't tell *us* about.
Anyway, 'glad you found it useful.
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