dwarf-fortress
When I try to build a screw pump with bMs, I see the red text:
Needs screw trap component
I've already built seven pumps, and still have blocks, pipe sections, mechanisms and enormous corkscrews to go. Nothing is forbidden, and no burrows are activated. What could I be missing?
Edit: It does work now, and AFAIK nothing changed. So the question is: What could I have been missing?
The thing about screwpumps in Dwarf Fortress, is that they can either be automatic (receiving power from a wind/watermill) or dwarf powered. Of these, only the former transfers power, as a dwarf manning a screwpump does not provide power, but rather sidesteps the power requirement entirely.
If however, you were to hook any pump in your pumpstack up to a power source with enough power for the entire stack (100 power in your case), assuming you built the pumpstack correctly, the power in the hooked-up screw pump will transfer to the adjacent screwpumps (and so forth).
Because of this behavior (it's the basis for the Dwarven Water Reactor), any pump with manual power will eject its operator if it gets enough power to operate automatically instead.
Have you seen this .GIF? It shows how to ensure the power transfers properly between levels.
Here's what you have:
If you channel that space and then rebuild the screwpump, power will flow between the connected machines and the screwpump below will no longer need to be manned (dwarfed?)
All screw pumps have two tiles -- one which the dwarves stand on to operate, and one which acts as a wall. This latter part needs to be constructed hanging over an open space to facilitate the transfer of power (as the former part must be constructed on solid ground).
A windmill produces 0, 20, or 40 power depending on the embark location. Each gear assembly consumes 5 power, and each tile of axle consumes 1, so your power transmission already consumes 12 power. A pump needs another 10, which brings you to 22 requirement. So if your windmill produces 20 power, that's enough for the whole power line, but just a tad too little for the pump.
According to the DF wiki page on pumps, pumps can be powered from below, but only on the output tile, and that tile must have its floor removed before construction of the pump.
Best Answer
Having items unforbidden is not always enough to make them eligible for constructing buildings.
My guess is that one or more of your Enormous Corkscrews had been scheduled to be picked up (that is to say, there was a dwarf moving towards it) or was being actively moved.
Once your dwarves put down your giant corkscrews, they'll become usable again, as you observed.