Wouldn't that just cause a solid natural ice wall to be dropped out of the caster?
Also I'm pretty sure being frozen in ice destroys all [ORGANIC] things, leaving metal and such behind, so it's possible that you could end up with multiple chunks of ice per tile if you freeze-mine-repeat without clearing the gathered ice.
Unless something has changed in the new version, only underground areas are safe from freezing (or underground and below the lowest ice layer if you're in a glacier), and exposing a square to light makes it permanently "above ground." So digging the piping for the water will be difficult. How you can prevent freezing is by placing magma beneath the casting area, HOWEVER, from the most recent ice science, magma has to be flowing to prevent freezing - it can't be static. How I can envision this working is if you have a caster that contains three layered elements: The casting layer (z3), the magma heating layer (z2) and the magma tank layer (z1 and z0) The magma heating layer and the magma tank layer would be separated by a retracting bridge, and the magma heating layer would be separated from the casting layer by a constructed floor. At the flick of a lever, pumps simultaneously start filling the casting layer with water and the heating layer with magma, respectively. The water will come through faster than the magma, but that's ok, because the magma should melt the ice as it goes. Eventually, the entire casting layer will be filled with water. A few ticks later it will all be ice, because the magma will have filled up the heating layer and therefore is no longer moving. At this stage, you just flick another lever to retract the bridge separating the heating and tank layers, and the entire contents of the heating layer drop back into the tank layer without any loss. There will be slight magma loss due to evaporation as the heating layer fills, but only a very little bit, and this can be solved by pumping the tank full to maximum whenever the caster is inactive.
||||
~__X_____|
|-%%.....|
|MMMMMMMM|
|MMMMMMMM|
_ constructed floor
~ water source
X floodgate
| wall
%% screw pump, magma safe and pumping from left
..... retracting bridge
- open space
M magma
Like this. This should let you cast a lot of ice to be harvested and quite quickly, with short "cool downs" between castings.