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[intently]

How about adding a 7/7 layer of water on TOP of the piston before dropping it. Then, if the magma is teleported directly above (and into) the water layer, you have an instant floor.

I think that would be counter productive to the magma pumping. For each level of the cistern (ie how far the piston drops) you bring up a 7/7 layer of magma. With water already there you would cast that entire 7/7 layer and gain nothing. in fact, the water on the sides of the shaft would cast the rest of the magma once it spreads out. The key to casting is to use as little magma as possible to turn into obsidian. Since one layer of natural rock can bring up 7/7 of magma, but only 1/7 magma is needed to cast obsidian (although I use 2/7 so there are no evaporation mishaps), then you can have a net gain of magma

I think McSmaster's idea is that when (if?) the magma is displaced it will end up ON TOP of the water.  The lowest level of magma would then turn into obsidian and hold in the rest of the magma, even if the piston/pillar is immediately lost to the SMR.  Possible?

[intently]

• Mine, don't channel. Channelling out the shaft takes a ridiculously long time and is dangerous for your miners. Just mine out the shaft and drop a floor from above when you are done to break through all the floors. You can mass designate the shaft by holding down the mouse and going up and down in long z-level columns. Designating 150 z-levels takes around 5 minutes, and digging takes less than a year with 3 miners

I tried this.  I mined out rings around the piston and then collapsed a floor above onto the top of the piston.  However, the piston didn't collapse when the floor hit it.  I believe the piston was being held up only by floors.  Can someone please elaborate on what conditions the piston must satisfy so that it will fall and break the floors when the floor above collapses onto it?

[Avaline]

• Mine, don't channel. Channelling out the shaft takes a ridiculously long time and is dangerous for your miners. Just mine out the shaft and drop a floor from above when you are done to break through all the floors. You can mass designate the shaft by holding down the mouse and going up and down in long z-level columns. Designating 150 z-levels takes around 5 minutes, and digging takes less than a year with 3 miners

I tried this.  I mined out rings around the piston and then collapsed a floor above onto the top of the piston.  However, the piston didn't collapse when the floor hit it.  I believe the piston was being held up only by floors.  Can someone please elaborate on what conditions the piston must satisfy so that it will fall and break the floors when the floor above collapses onto it?

It took me a bit to get that as well.  There may be an easier way since my method was more involved than the piston itself but here it is:

Step 1: Decide how big you want to make your piston.  Make sure that you have a plan on how to get magma into the bottom of it though don't do that yet.  Note that you'll also need at least three floors of earth above where you'll want the magma to go (those who are VERY Dwarfy can find a workaround that one).

Step 2: Mine a ring around the piston to be along every floor of the piston.  in the end, you'll have a ring from the very bottom where the magma will go all the way to one floor ABOVE where you want the magma to end up.

D = mined out spot
Top view:
DDDDDDD
D         D
D         D
D         D
DDDDDDD

Side view:


D            D
D            D- Where magma will end up
D            D
D            D
D            D - Bottom

Btw: Count the number of spaces you dug out in one floor.  Add 2 to that number.  That's how many Magma-safe Floor Hatches you need so start making them.

Step 3: Listen close to this one.  TWO floors above your last dug out area, channel out a room that's the size of piston-to-be and DIG make a ring around that as well.

Top view: (C = Channel, D = Dig)
DDDDDDD
DCCCCCD
DCCCCCD
DCCCCCD
DDDDDDD

Side View:
DCCCCCCD

D            D
D            D- Where magma will end up
D            D
D            D
D            D - Bottom


Step 4: Plop a Support somewhere on that top most ring you just made.  Stick a lever somewhere within reach and attach the support to the lever.  AFTER this is done, Channel around the ring.  The result is this:
CCCCCCCCC
CDDDDDDDC
CDCCCCCDC
CDCCCCCDC
CDCCCCCDC
CSDDDDDDC
CCCCCCCCC

(Bold and underlines done for easier reading.  Note that the Support, "S" can be on any spot of the dug out area)

Note: If a dwarf gets stuck, use a floor hatch to let them escape.  You may end up losing the hatch when it's over though but don't worry (remember how many I told you to make?  It was 1 more than you really need.     ).

Step 5:  Go one floor below and you'll see a newly made room with a ring of natural wall side it.  Dig out that ring so you have this

DDDDDDDDD
DDDDDDDDD
DDDDDDDDD
DDDDDDDDD
DDDDDDDDD

One big open room, below the top floor with the Support and above the rest of the Pillar-to-be.


Step 6: Evict ALL dwarves from the pillar area.  Hatch over the stairs and lock it if you have to. 

Step 7: Pull the Lever

End Steps

The result: that dug out ring with the Support at the very top is being held ONLY by that support.  Without it, it'll cause a cave in crashing through the open floor below it, then below every dug out ring all the way to the Bottom. 

If it goes well, you'll have Two floors of open air, followed by a large block of earth surrounded by a ring of open air all the way to the Bottom.  Congrats, you now have your Piston.

To do the final setups, Make some flooring one floor above the piston, put up a Support (and link it with a lever) where the piston starts so it's attached to the floor, and set up your hatches one floor BELOW where the piston begins.  Result:

Floor Above: (F= Floor,  O = open space)

OOOOOOO
OOOOOOO
OOOFOOO
OOOFOOO
OOOFOOO

Next Floor: (G= regular Ground, S = Support)

OOOOOOO
OGGGGGO
OGGSGGO
OGGGGGO
OOOOOOO

Floor under That: H=Hatch

HHHHHHH
H         H
H         H
H         H
HHHHHHH

AFTER this is done, go to the very bottom, dig out that whole area and pump magma into it.  Meanwhile, once all dwarves are away from the area, put Walls up to completely seal the floor with the Hatches and make sure there's no openings or stairways.  Remember, there will be magma in there in a minute.

After all that, Pull the lever.

If it works, you're done.  Congrats on your piston! 

(note, I found that when I did it, I ended up with a room of magma that was 3/7 or 4/7 filled since the room the magma goes into is bigger than the amount that was pulled up.  It looks like I'll have to pool up the magma somewhere.  Small detail when I just dragged it up 50+ floors with FAR less resources than a mass pump stack.

Btw: if the above seems a mess and dangerous, it's FAR less dangerous than simply channeling the rings out since the miners WILL end up causing a cave in at some point unless you, manually tell them to channel out one floor at a time.  Thus channeling is either A LOT more dangerous or a LOT more tedious. 

[intently]

Thank you for the diagrams!  This is basically what I was doing, except that I was dripping the ring of stone onto the piston instead of AROUND the piston.  I thought it would hit the piston and then push the piston down.  In reality, the falling ring of stone will knock out all the floors in the mined out ring around the piston.

Also, I made a "cup" of channels on top of my piston to catch the magma rather than bother with all the hatches.  We'll see if that works.

[Avaline]

On part 1:  Nah,  The whole point to the ring caveins are to create the piston in the first place.  Without that, the floorings created by Digging hold the piston up. 

The method I describe is technically untested.  What I actually did was messier, instead of channeling the whole top and leaving just a ring, I channeled around the top and bottoms of the ring, caved in them, then channeled the sides to make cave ins for those.  Though I didn't actually DO the one I wrote, it should be MUCH easier and safer.

As for the Cup... I LIKE.  Just remember that unless you plan out your piston carefully, the pool of magma in the 'cup' will take up more than one floor (The pour a 2 liter into a cup situation).  Chances are, it'll look like this:

Top view:

Upper:

OOOOO
O      O
O      O
OOOOO

Middle

333334
3       3
3       3
334433

Bottom

777777
7      7
7      7
777777

O = Open space.  numbers = magma depth.  Note that the Middle numbers may vary.. you could have 1's and 2's, 5's and 6's or anything.  Also note that some number crunching can help you know just how much to expect.

Whatever it comes out to, a little digging/pumping/whatever can fix it easily and give you a nice magma batch to set up shop over.


Myself, I plan on taking my 3/4 depth magma and pumping them into little neat pools so that all I'll have is nice 7 depth pockets for my shops. 

[Fenwah]

Also, I made a "cup" of channels on top of my piston to catch the magma rather than bother with all the hatches.  We'll see if that works.

Even though i used hatches and mentioned hatches in most of my posts, retracting bridges would be far, far better to catch the magma with. They function exactly the same for this purpose as hatches, and can be built much easier. The only reason I used hatches is because I didn't fully understand how bridges could be used when I built my pistons (specifically, that retracting bridges can be built entirely over empty space. I had assumed that they needed to have an 'anchored' tile like raising bridges)

[intently]

As for the Cup... I LIKE.  Just remember that unless you plan out your piston carefully, the pool of magma in the 'cup' will take up more than one floor (The pour a 2 liter into a cup situation).  Chances are, it'll look like this:

Top view:

Upper:

OOOOO
O      O
O      O
OOOOO

Middle

333334
3       3
3       3
334433

Bottom

777777
7      7
7      7
777777

I don't think that will be a problem.  The cup is inset into the top of the piston, so 7/7 lava should cover both the inside of the cup AND the top of the rim of the cup when the piston lands in the lava pool.  The lava on the rim of the cup should just leak over the sides and down the piston shaft.  Then I can build floors or whatever to cover the ring-shaped opening of the top of the shaft and build my magma workshops on the rim of the cup.

In theory!

[ouroborus]

A few things I'm not clear on.

How do you deal with the caverns that are likely to be between the lava and the surface? (Reread the OP)

How do you go about recasting multiple layers at the top? As near as I can tell, people are saying that you can only cast a singe layer at a time and that layer has to be sitting directly on the piston. It seems to be implied that you have to cast the layers one at a time which means pumping lava both in and out of the area at the top of the piston.

How do you cast the layers without the piston hanger getting in the way?

[kendo]

I tried this using the method Avaline described. but all that happens when I drop my piston is the magma only moves up one or two levels, it never reaches the hatch level. The cavein seems to create a floor at the base of the piston where my channeled out ring was was - with magma on it and then the level above that - 'open space' and 'magma 4/7.

The top of the piston is the only sign of the magma rising - its covered in 1/7 magma. Its very confusing.

Edit: I think maybe my piston is too big (thats what all the girls say) - the piston is ending up 2 floors below the hatch ring level (i started the hatch level one below the top of the piston) with magma dusting on the top. So I suppose the giant hole where the piston used to be on the hatch level is letting all the lava escape, I must have read something wrong or got the dimension mixed up.

[Fenwah]

How do you go about recasting multiple layers at the top? As near as I can tell, people are saying that you can only cast a singe layer at a time and that layer has to be sitting directly on the piston. It seems to be implied that you have to cast the layers one at a time which means pumping lava both in and out of the area at the top of the piston.

How do you cast the layers without the piston hanger getting in the way?

Yeah, you have to pump out most of the magma, cast, dump some back in, cast, dump more in, cast, etc. Once you rebuilt the piston just empty out all the magma that is left in the sides and you are done. Its a bit fiddly but with some practice its not so bad. If you look at the map I posted you can see that I just used a short term reservois directly above the piston to dump magma in.

Also I probably should have mentioned this in the OP (I will add it) but I had issues with how to suspend the piston. Like you mentioned, a hanger would get in the way of casting. I also tried having the support grounded off to the side, connected to the piston by constructed walls and floors, but when they fall they smash the hatches below.

The solution I found was to just put the support in the cistern (everything magma safe of course). Since supports don't block fluids, it didn't reduce the amount of magma I could bring up at all

I tried this using the method Avaline described. but all that happens when I drop my piston is the magma only moves up one or two levels, it never reaches the hatch level. The cavein seems to create a floor at the base of the piston where my channeled out ring was was - with magma on it and then the level above that - 'open space' and 'magma 4/7.

The top of the piston is the only sign of the magma rising - its covered in 1/7 magma. Its very confusing.

Edit: I think maybe my piston is too big (thats what all the girls say) - the piston is ending up 2 floors below the hatch ring level (i started the hatch level one below the top of the piston) with magma dusting on the top. So I suppose the giant hole where the piston used to be on the hatch level is letting all the lava escape, I must have read something wrong or got the dimension mixed up.

You must be building your ring too high. Run through the numbers again and you should be alright. Remember to keep in mind that if the piston falls down 3 levels, you need to have the ring of hatches or bridges 3 levels below the topmost floor of the piston (assuming its flat). If you are in doubt, build another ring a few levels lower, so if it does fail you will not lose everything.

[rmunn]

I read this thread with great interest and I'm looking forward to trying this myself, but there's one thing I'm not clear on.

Things to remember

• If your piston has bits missing in the middle because of caverns, anchor the bottom section, and drop the top parts. The gaps will fill and you can then clean up the top of the piston

What do you mean by "anchor the bottom section, and drop the top parts"? I'm new to DF, and I thought I understood how cave-ins work, but this doesn't fit with my understanding. If the bottom section isn't anchored, then it's already falling... right? Or, in other words, if your bottom section isn't caving out from under you, then you've already anchored it. I think. So what exactly are you doing here -- how are you getting past the "hole" a cavern makes in your piston?

I'm a visual learner, so if the answer is complicated, a diagram (or a link to a map showing before-and-after of dealing with caverns) would really help me understand it. Thanks a bunch!

[keda]

You can simply clean out the cavern section of the piston so its flat and then drop the top section on the bottom one. I guess what Fenwah means is that its already only being supported at the top, but the bottom section would otherwise fall when you flatten the cavern section.

[intently]

Edit: I think maybe my piston is too big (thats what all the girls say) - the piston is ending up 2 floors below the hatch ring level (i started the hatch level one below the top of the piston) with magma dusting on the top. So I suppose the giant hole where the piston used to be on the hatch level is letting all the lava escape, I must have read something wrong or got the dimension mixed up.

I say to forget the hatches.  Just channel a "cup" into the top of your piston.  This cup will fill with lava when you drop the piston.  The "rim" of the cup will get lava also, but this lava will quickly leak down the shaft.  You can then build floors or whatever to close off the top of the shaft, and then build workshops directly over the lava.

[kendo]

Yeah I got the hatch system working, for me it needed to be 4 floors down from the top of the piston, but its a bit messy  - a cup like you say would be far easier to set up.

[Fenwah]

You can simply clean out the cavern section of the piston so its flat and then drop the top section on the bottom one. I guess what Fenwah means is that its already only being supported at the top, but the bottom section would otherwise fall when you flatten the cavern section.

Yeah, I that's pretty much what I meant. Sorry, I wrote most of the OP based on my experience from making the first prototype, where i had a single solid piston section, but there was a few bits missing on the corner I had to clean up. This meant anchoring the bottom section, separating the top and bottom, dropping the top, and flattening it out. If you're sections are already separately anchored then you are good to go, so long as the cave in doesnt smash whatever support you have set up