So even if the layer is 7/7 water magma starting on the level above it won't evenly solidify the layer?
On the matter of pumping throughput: how fast have you seen a beefed up single pumpstack go? I'm looking at casting around 150k units of obsidian here. The bottom 30 or so layers are all going to be massive 50x44 regions. I was figuring that a single tile of entry would restrict the flow too much, hence the 9 wide entry point.
Exactly. Water being flowed over the top of magma = Good casting. Magma being flowed over water = Spotty casting.
As for your 50x44 regions, think about it. That's only 2200 tiles. Given that a properly made pump stack will supply 7/7 per tick. That means 2200 ticks. Assuming you have a fps of 100, that's a mere 22 seconds. (Lower fps of course will result in slower filling). As for a single tile being "too restrictive", that's nonsense.
As for someone else suggesting that you use the magma sea and avoid magma pipes, that's questionable. Frankly, magma pipes make one of the best rapid flow sources of magma out there. There are three mechanisms in which a "natural body" of fluid moves from place to place within dwarf fortress. I'm going to call them
1. Pressure mechanics.
2. Flow mechanics.
3. Gravity mechanics.
Pressure mechanics is the fastest method. But in general, it only applies to water. If you have 2 or more Z levels of fluid "stacked" on top of each other, you can tap into the lower layer and draw off fluid. And what you draw off will be INSTANTLY REPLACED by fluid existing at a higher Z level as rapidly as you can draw it off until there is no more fluid available on a higher Z level. Pressure mechanics is why I tend to dig my water cisterns at the bottom of the water pump stack. It lets me maintain 7/7 flow per tick for quite a while, without requiring multiple feeder pumps.
Flow mechanics is what happens with unpressurized fluid moves over a horizontal distance. It's very slow and quite feeble. This is unfortunately, the primary method of magma flow. You suck out some magma via a pump and the magma needs to be replaced via flow mechanics before more magma is available to be pumped. Painfully, painfully slow.
Gravity mechanics is simple. Namely if you have a stack of fluid (say like that in a magma pipe), and you take from fluid from the bottom, the fluid above will fall and instantly replace what was taken.
So with a magma pipe, you can take advantage of gravity mechanics to make the distance that flow mechanics has to work over very very short.
Here are a few screenshots of my magma supply under construction.
This top image is my power distribution to the pumps. Rather complicated and messy looking since my objective isn't to minimize power routing. It's to minimize the distance from the magma pipe to the intake of each of the pumps at the lower level. There is a gear built over a channel of the impassable tile portion of the pumps below to transfer power to 6 of the 7 pumps. The last pump gets its power directly from the pump above using the conventional method for a pump stack.
This image shows where the feeder pumps are going to go. You'll notice 7 iron grates where the pump intakes are going to be located.
And finally, where the magma is being supplied. Just a simple channel following the perimeter of the magma pipe. When my miner gets around to it, about 1/3 of the perimeter of the magma pipe will be dug out. I don't expect any dwarves to die since the obsidian walls will be dug out using the above diagonal "exploit" although I do expect a bird or two to be roasted since the screen shots don't show the couple of fowl that didn't bother to get out of the area when I build the wall sealing off access.
In any case, when those pumps start working, they're gonna empty the tiles they pump from, and those tiles will be replenished over a distance of only 2 via flow mechanics because gravity mechanics will keep those tiles within the magma pipe proper at 7/7. And a distance of 2 with all those other tiles filled to 7/7 isn't too bad for flow mechanics.