- Nov 23, 2016
- Reaction score
After two attempts at casting a brass ring I got a good one. The first one failed because I did not have large enough gates and the melt cooled before it got all the way around the mold You could see the rolls in the ends where it cooled like lava. Second mold I had the gates as deep as the ring and much wider. I also made a 2" cup riser like Mark suggested and an 1-1/4" vent riser 180 degrees from the pouring gate. I also poked 1/8" vent holes at 4 evenly spaced marks in the ring pattern. I had the brass actually boiling when I took it out of the furnace and poured immediately. Wow was it hot! When the brass flowed up the vent like a volcano I new I had a complete ring cast. But as I watched it cool I was amazed how much it shrunk in the risers again like Mark said. I was afraid it would shrink all way down to the ring and leave a bad spot there. It finally stopped and hardened in the spout. When I broke the sand off I had a good brass ring 9- 1/2" in dia , 1-1/4" thick with thickheavy gates,4, 1/8" tits about an inch long sticking up where I poked the holes. So it went well and hopefully it will machine well. I forgot my camera but will take pics Thursday when I go back to work. Thanks Mark and myfordboy for all the wonderful helpful youtube posts.Hey Jim - I'm pretty sure the ally would melt.
I echo what Oilmac said about getting too hot - that's happened to me several times, and one or two folks have said to me that those pits are to do with dissolved hydrogen.
Have you had a go pouring brass yet? Seems like a good idea while you have the kit laying around. I found advice on-line to throw some glass in which forms a sticky-toffee lid - it's meant to hold the zinc from burning off, and to give the dross something to stick to. Make your rim a bit big so you can clean it up in the lathe, and *make sure you have a good bit of sprue sticking up* (Oilmac's extended risers are a good idea) since the brass will cool at the edges of the sprue and feed down the middle as the interior cools, leading to a kind of 'tube' forming in the sprue.
Oh - and the advice you read about having a fat riser coming off heavy bits in the pattern is good - I suffered from shrinkage problems by not doing that, recently - easily forgotten.
Hold your breath around it - zinc fumes coming off are best left un-breathed!
Jim in Pa