I guess an alternative would be to drill a 1-tile wide pit to the bottom with notches every few points, and build the drill from the inside making use of a chian-reaction.
R= rock or natural ground, S= spacer (gravel/sand), T= TNT
These setups can be detonated from above and chain to the bottom-most. Only work needed is minimal drilling downward to the bottom, and taking a break every few tiles to place TNT. Blueprints are as follows (90 degrees):
RRRTRRRRRTRRRRRTRRRRRTRRRRRTRRRRRTRRR
TSSSSSTSSSSSTSSSSSTSSSSSTSSSSSTSSSSST
Alternatively (for more fun, and guaranteed chain)
RRTRRRRRTRRRRRTRRRRRTRRRRRTRRRRRTRRRR
TSSSSSTSSSSSTSSSSSTSSSSSTSSSSSTSSSSST
RRRRTRRRRRTRRRRRTRRRRRTRRRRRTRRRRRTRR
EDIT:
Whelp, I finally caved in and got me a few editors and whatnot. I think it should make some of my experimenting (and designing) easier. However, I'm keeping World2 (where I keep on talking about in my posts) a full-legit game (with the bed-teleporter save-translocators to jump long distances sans inventory). But I made a copy of it as World 4, and am using it for experiments and designing stuff before actually working on them.
EDIT EDIT:
After "adjusting" my inventory a tad, I made the 1x1 pit with 1 TNT every 3 tiles above the previous one in the alternating pattern I sketched out, and it works like a charm, provided one of the TNTs don't fly out of the hole (in which case, one flew right at me, and killed me, and interrupted the process. I recollected everything at the bottom of the pit (and detonated the bottom-most one that was left), which explains why I had to climb out with what ladders and jumping skills I had.).
When I initially tested it out, I messed up and filled the buffers with cobblestone instead of sand or gravel, and it didn't work, but I redid it with a different site, and used gravel instead, worked like a charm, and now there's a rather decent void in the area that delves deep, and all I had to use was a plausible amount on TNT close to the amount I already have in store to make the shaft.
Of course, to make testing swift, I had to use diamond tools for experimental purposes, and worked on it with raw terrain. It's beautiful. I'll screenshoot the results.
From the bottom of the shaft
Inside to the blast zone (as you can see, I used ladders and a little parkour to get out of the hole)
Away from the blast zone (but still within)
And the lovely crater with the wildlife undisturbed.