How can I tap my magma without haveing it overflow into my entire fort?
You may have to use the very old technique of scratching a fortification into your volcano pipe. Okay, let's do a step-by-step.
- dig a tunnel below your future magma workshops and then tunnel your way towards the volcano pipe.
- get some magma-safe floodgates, grates and levers ready.
- position the floodgate at the end of your tunnel, directly next to the volcano pipe.
- connect it to the lever
- put a dwarf into the room of the lever.
- have another dwarf smooth and fortification the magma pipe. Just one tile of it, else he'll burn to death
- while he's carving the fortification, give him another engraving job somewhere else so that he won't linger and get burned to death
- as soon as the magma is pouring in, have the lever pulled
- now you need to wait a short while until the magma has evaporated
- then place a (W)allgrate behind the floodgate
- feel free to construct another wall behind the wallgrate and to carve another fortification into it
- feel also free to place more wallgrates
- and then let the magma flow in. This should be safe against all magma critters. Magma men can't really fit in through the fortification; and the smaller ones can't destroy the grates or the floodgates.
If you want to have more magma than just for your workshops, poke the volcano pipe some more with the same technique.