I am really enjoying the SP14 Moon Phase clock that I built from Steve's plans. It is far more accurate than I would have imagined; until I opened the windows this spring and heated up the room. Now the clock runs about 1 min per day slower. Easily adjusted for, but as an engineering curiousity does anyone know of a material I could try that has a lower thermal coefficient of expansion to see if I can minimize this sensitivity? All pendulumn parts are currently eSUN PLA+.
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Thermal Coefficient of Expansion and Pendulumn Length
Thermal Coefficient of Expansion and Pendulumn Length
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Great question. Google "coefficient of thermal expansion" to get a list of changes per degree of temperature change. Plastic is typically about 3x worse than brass or steel. But, as you have noticed, modern houses with heating and air conditioning really only change temperature by a few degrees twice a year.
Two of my oldest clocks, SP2 and SP3, used carbon fiber rods which should have very low thermal expansion. It added to the bill of materials and added extra assembly steps. The clock wasn't really any more accurate so I switched back to simple printed pendulum rods. This works well enough as long as the temperature changes are minimal.
Maybe the "carbon fiber" archery arrows I used were not actual carbon fiber, but closer to plastic with a few bits of fiber embedded. I never actually tested their expansion rate. There is another material called invar that is very close to zero expansion. It is expensive.
Other options include taking advantage of the differences in expansion between brass and steel to build a gridiron pendulum rod. Or use plastic and steel. It would add a bit of complexity.