>That's a matter of stabilizing it dimensionally before they do any >critical machining on it. It's not that the casting actually shrinks >during this cure time, it's the warpage. Machine tools also need to be >free of the warpage which result from the internal stresses relieving >themselves, before you can start milling and grinding the reference and >working surfaces into them. > >But I'd never heard that the cast iron pickled up strength. Only that any >close tolerance work you might do on them would be wasted while they >continue to warp. Sort of like expecting to do a concert grade tuning on >fresh wire barely chipped that afternoon. > >Bill Ballard RPT Like reaction wood, that is nice and straight until you rip it, then curls like crazy. I presume we're talking about months after it's cooled from casting and just lying around de-stressing. So the presumption is an internal creep, that stabilizes it after a time? S&S plates that have been lagged to the rims for a hundred years still spring up when you pull the lags - sometimes quite a bit. I'd understood the long cure time was to minimize the possibility of cracking under load in areas that shrink at different rates and in different directions during cooling. Again, a sort of long term internal creep. Seems like something that's been done for a thousand years would be easier to get clarification on. Ron N
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