I have a transparent round box of a camera lens filter and it would be achallenge for me to replicate this in metal. I chose brass and made the mold. The inner rim is about 10mm high and not tapered. Despite this, the sand did not stick after gently tapping the outside. I put the open end in the cope, so it was flat on top. The first time it failed, probably due to too cold metal. Then I made a new mold, same as first time, but pricked with a nail several holes in the cope (of which one even filled with metal later !) when the pattern was still in the mold. And I put the flask a bit skewed (15-20 degrees) like I did with the cast iron sundial. I let the brass become hotter (1100 C), cleaned all dross (that is a big disadvantage of brass) and poured. The casting turned out well, except some minor errors (last photo on top, an incomplete filling in the rim).
Cool! We love some good thin wall castings here at Lodge! Every year they keep getting thinner and our scrap reflects the degree of difficulty in being so thin. Speaking of thin wall castings this is kind of a rough idea of how we do it. I am speaking only in reference to cast iron as all other metals I have little to no experience with. Many of our castings have an ingate contact point of .040" to help with inclusions and to break off easier. We pour some of our biggest jobs with .040" contact points. If you stretch that contact point out over a longer area you can cut way down on the thickness. You distribute the heat evenly over the whole casting and not just at one point. This is the easiest way to make thin wall castings...you need some pressure to push it into the castings and spread the heat out as far as you can. Try it again one day with a much thinner ingate (1mm or less) and try wrapping the ingate around at least half the casting and see if it works as well or better with much less clean up. It may be a complete failure due to my ignorance of brass but would work or come damn close with cast iron....also heat your sand up slightly to keep thermal loss at a minimum. But anyway....Congratulations on pouring the thinnest brass I have ever seen poured by hand!
