All materials 'move'. A blacksmith friend showed me how badly it moved with a few bangs of his hammer on mild steel. You can 'easily' stretch, widen, flatten, elongate, steel and most metals. Getting them to stay in one place over the long haul is almost impossible.
Still metal workers do a better job of it (due to usually using the same type of material - steel, brass, aluminum, titanium, tec) than woodworkers do. Wood moves due to weather (mostly humidity, metal moves due to temperature and physical abuse), and wood moves much more and more erratically than metals. (Listen to a few WoodTalkOnline podcasts, wood movement is a constant issue, especially when doing 'cross grain' work). There are some good video's out about cross grain 'bread board ends' and how to NOT hard attach the ends to the long boards, but to attach it in only one location (typically center) and leave other 'alignment pins' in elongated holes to allow movement (so the assembly won't tear itself apart). Plastics of all kinds (epoxy's, ABS, PLA, TFE, etc) all move, typically due temperature or mechanical abuse, sometimes chemical. In metals, Aluminum is very thermally active and moves more than steel with temperature changes. There are reasons why big rocks break to make small rocks. Temperature changes and physical abuse (like water getting in cracks, doing some erosion, but often it freezes and expands (water is the densest at 4C (39F) and expands getting warmer or colder, even when in ice form - this is from memory for current info, we need to find someone more informed than I am) In the last few years I have befriended a 'concrete geek'. I have found out more about concrete chemistry, fracturing, curing, flexing ability than I ever thought. Even simple concrete isn't simple, let alone finishing, forming, and uses! Materials science can be facinating but for most of us, just knowing that nothing is absolutely stable is helpful. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
