How to mine out a pump stack shaft

dwarf-fortress

I am trying to mine a shaft for a pump stack, but the miners are only mining a couple random tiles per z-level. Here is my digging designation: (M=mine, C=channel, .=no designation

Z level 0

...M
CMCM
...M

Z level -1

M...
.C.C
M...

Z level -2

...M
C.C.
...M

(levels -1 and -2 repeat alternating all the way down

The idea was, for example, the channel from layer 0 to mine out access to layer -1, resulting in a pattern like this: (#=rock, ^=up ramp, v=down ramp, .=mined out)

Layer 0

######
####.#
#v^v^#
####.#
######

Layer -1

######
#.####
#^v^v#
#.####
######

Then, I'll go back and clear the center up ramps, leaving 1 floor and 1 hole to build head-over-tail pumps on, that will draw from a 1×3 reservoir from the layer below.

My miners have dug the entire depth of the shaft, but have missed several (seemingly random) tiles on each layer, and now say "no job".

Why doesn't this pattern work?
How can I make this structure with a minimum (or even better, no) constructions?

Best Answer

Ramps don't work the way you think they do. The ramp (resulting from a channel) has to be next to a solid block, which has a floor above. The ramps in your design are invalid (because the only solid blocks they're next to have solid blocks above as well), so the dwarves just treat them as holes in the floor, so they can't get to the far side of the hallways, and can't move up and down the stack.

Self-transmitting pump stacks like this pretty much need to have side access. This is the way I always construct them (edit: adjusted for larger reservoirs):

Level 0
######
####+#        M           # = rock
#.+.+#     CMCM           + = floor
##+#+#      M M           > X < = stairways
##+O##      MM            . = channeled space
##>###      D             O = mined out, then wall constructed

Level -2n+1
######
#+####     M
#+.+.#     MCMC
#+#+##     M M
##O+##      MM
##X###      X

Level -2n
######    
####+#        M
#.+.+#     CMCM
##+#+#      M M
##+O##      MM
##X###      X

Once you have this shape as deep as you need, you can build the pumps in the middle of each floor. The dwarves use the stairways to get up and down. You still have to order the channel in the middle of each level last, because once it's channeled the dwarves can't reach the area that will be the reservoir. Also, your miners will invariably channel from the wrong side and trap themselves.

An alternative (and safer) method is to designate each level from the top down, and wait for it to be completed before designating the next level. That way the channels will be safe (functioning) ramps while the reservoir is being dug out. However if you do this you have to use the "remove upward ramps" designation rather than the "mine" designation.

I've edited the answer again to show the one constructed wall I recommend making on each floor, so that the dwarves can get in and out of the reservoir area during construction. Note that because this constructed wall is adjacent to the reservoir only diagonally, and dwarves won't make constructions diagonally, they can't build this wall from the wrong side and trap themselves in the reservoir.

For extra fun, try extending this pattern above ground, with constructions. It isn't easy!

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