So today I was able to get a 1/4-20 tap and test it out on epoxy that had been set in an enlarged holes in a piece of scrap wood. The epoxy had been completely cured for a week. It worked much better than I would have thought.
I did it in 100 degree temperatures in the direct sun. Not ideal as the tap, wood, and cured epoxy were are almost too hot to touch. Even so, starting it with a tapered tap then finishing with a blind tap worked really well despite the expoxy getting slightly softened with the heat.
Comparing it to the cast threads I found the tapped threads to be slightly loser. I used a 13/64” bit instead of a #7 bit for the hole, but i doubt if that would make a difference. the advantage of the tapped threads was that it was easier to ensure that they were perpendicular to the wood surface and would be easier to be precise in the location.
So, rather than casting I think I will drill and tap. The next test will be with expoxy thickened with West System 404 instead of the colloidal thickener that I have used in my tests so far.
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