A request for some education.
Occasionally, I hear/read about people having had problems with cast iron tables or extensions warping over time. I’ve not encountered this, but am curious about how it comes about.
My understanding is that warp of cast iron occurs in the face of rapid temperature change, and that it’s inherent to the nature of cast iron, though the tendency can no doubt be ameliorated by design—e.g., thickness, support, etc. But is this the entire story? When I hear someone complain about warping of a cast iron table extension, as a brand-specific criticism, I’m never quite sure what to make of it. Are such critiques implying faulty design? Something else? Are there significant differences between various “cast irons” that lead to relative resistance or susceptibility to the phenomenon?
Thanks to anyone who can enlighten me a bit or point me in the direction of more/better knowledge.
Replies
Metallurgy was my minor but I am not an expert.However in the old days cast parts were stacked in the yard before machining to assist in relieving stress.That said,current cast iron is different but is subjected to some warping or twisting after machining.My friend purchased a very expensive planer joiner whose outfeed table twisted.Everyone needs a machinist straight edge to measure their machines
Back in the day, they let cast iron sit and age for a long time, to let it do whatever it was going to do. Something like stacking wood after sawing. Then they would machine the cast parts, after the aging.
I have no facts to support this, but I wonder if manufacturers rush things today, and machine tables before they are aged. I've never heard of an old machine warping down the road, only recent manufacture.
If I understand correctly, cast iron, after initial forming, is subject to stress-relieving twisting warping of some degree. Probably affected by process and particular alloy, etc., but, there it is. To avoid difficulties with this in machine parts, makers used to let cast iron sit and “age” before machining, so that whatever stress relieving was necessary was done before machining to final dimensions.
Modern makers, it seems, don’t always (or even usually?) allow for adequate aging of cast iron before machining, thus presenting the purchaser with parts that may still be undergoing final stress-relieving movement of crystals, and thus, the part. And so we get tables, extensions, etc., that may warp even if properly cared for, with no exposure to dramatic temperature fluctuations, etc.
Do I have this right?
That's my belief. But I'd be glad to hear from someone who's worked in the field.
Thanks. This makes sense, and I’ve now learned something today. Much appreciated.
You can bet that in today's streamlined manufacturing (of everything) nothing is aged.
A few companies (like the now defunct Steel City) tried granite table tops on their tablesaws to assure dead-flat, warp-free surfaces. Not sure the concept has caught on or advanced.
I’ve seen some ads/descriptions of that sort of thing, for jointers, etc., and see it as...intriguing. Granite of course can be made exquisitely flat, is very durable, etc. But...it’s susceptible to cracking and chipping, though I don’t know the actual propensity of the material for same, and it would of course be dependent on specifics of grain, thickness, support, and more. Given my conservative nature about messing around with what’s worked before, I’m not inclined to lead that parade, and also given that I’d wanna see some meaningful data over probably at least a decade or so, I don’t see it as likely to make it into my shop soon. Though I’m happy to point out that I’m open to evidence and persuasion on the matter.
It’s possibly an issue in a machinist shop, but not ww’ing.
There are some, though, including some who’ve posted on this forum, who report after-purchase warping of cast iron tables, extensions, and the like, to an extent that it affects their woodworking practice. I suppose it’s possible that mis-shapen or already-warped/twisted tables in some cases only become noticeable later, but I’ve heard from a fair number of directions that previously fine setups have gone wonky, usually within a few months to a year or two of purchase.
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