I wanted to build a precision vise to use with my 3-in-1 lathe/mill/drill. I found a design on the web and I started to build as designed. I started this project last fall but winter shut me down before I could complete it.
I cast with greensand but I used foam to build the pattern. I have a hot wire cutter, roughing shapes is very easy. My intention was to cast billets which I would machine, but this was very wasteful and time consuming. I got the base formed and I was getting ready to cast the next part when it dawned on me, why do I need to bolt the parts together when I can cast it as a single part. Additionally I can make a core that would make machining simpler. So I built a new vise pattern out of wood and an mdf pattern for the core.
I have never made a core before, there is a first time for everything. I purchased some Sodium Silicate and now I was searching for a way to generate carbon dioxide to harden the core. I don't have any compressed CO2 so I thought I might used baking soda and vinegar but then I remembered my kids making geysers out of diet coke and mentos. I cut an empty coke bottle in half, placed it and the core in a small cooler added ~2" of diet coke dropped two mentos and closed the lid. I didn't know what to expect, I removed the bottle neck so I was fairly sure that I wont have a geyser but will it harden the core.
Worked like a charm! I wanted to be certain that the CO2 would work so I left the cooler sealed for an hour. I have seen vids where the core hardens fairly quickly with CO2 gas but I was uncertain how much CO2 would be released from the diet coke. The results were great, I got a hardened core.
I had an opportunity to cast this morning, I estimated the weight needed at 5 1/2 lbs of Aluminum. This is the first casting with my newly resurfaced furnace and the new oil burner. When I casted the original part in the fall it took about 20 minutes from start to pour, this new burner got the job done in 10 minutes. It takes me longer to set up the furnace than it takes to melt and cast.
I had a bit of shrinkage next to the riser, I knew that part of the pattern was bulky and probably would shrink so I places a 3/4" riser. It was not enough, I needed either a taller or wider riser. The pattern was made over-sized with the intention to mill it down to size so this may not have any consequence. I still have the slider to cast and then machine the castings, more to follow.
EDIT: cut the gate and riser, the shrinkage was 1/8". The surface is OK a little mottled but it will be machined, but I am undecided whether I should recast to eliminate the shrinkage.