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Choosing between a new core box or patching the old one for a big gray iron job
We had a rush order for 50 gray iron gear blanks last month, and the old wooden core box for the center bore was splitting. The choice was to spend two days building a new aluminum box or try to patch the old one with epoxy and clamps. I went with the patch job, mixing a high temp epoxy and clamping it tight overnight. It held for the first 30 pours, but on the 31st, the patch failed and we got a bad shift in the core. We lost half a day's production cleaning the sand system and recasting. In the end, the quick fix cost more time. Has anyone found a reliable epoxy for wood that can take the heat and moisture long term, or is building new always the better call?
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iris_mason882mo ago
Epoxy's just a band-aid for wood.
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the_michael2mo ago
Okay iris_mason88, that's a strong take. When you call it a band-aid, do you mean it's only for hiding damage, or that it always fails over time? I've seen some epoxy jobs last years on table tops if the wood is totally dry and stable. But if you pour it over wood that's still moving, it's going to crack for sure.
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the_jason15d ago
It really depends on what kind of epoxy and wood we're talking about though. I've seen guys use the slow cure stuff on green wood bowls and it actually soaks in and stabilizes the cracking so the piece is still functional. The problem is everyone grabs the five minute hardware store tubes and expects it to fix water damage or rot.
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When iris_mason88 calls epoxy a band-aid, I feel personally attacked because I've got a shelf full of epoxy that's basically become a museum of my failed quick fixes. That gray iron job you mentioned - I tried patching a wooden pattern once with that same high temp stuff, and it held just long enough to make me think I was a genius before it gave out on pour 47. The mess was worse than if I'd just built a new box from scratch, and I spent the next two days picking epoxy chunks out of the sand like some kind of archeologist of my own bad decisions. If the wood is even a little bit damp or the core box sees any steam from the sand, that patch is going to fail, and you'll be paying for it in lost time and scrap.
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