Did a bit of research, but someone who knows Bleach please check my work. ("双極のタッカ is the giant cleaver that was going to be used to kill Rukia, and which Ichigo later destroyed")
GIS reveals the most common use of タッカ to mean a staple-gun or "tacker". Perhaps there is a related meaning here in that the victim is "tacked" to the frame à la crucification. Or perhaps due to the fact that the frame itself is staple shaped?
I looked at a raw version of the chapter 152 page. たっか is merely the furigana provided for 磔架. One of the on's of 磔 is たく and the on of 架 is か. So we get たっか.
For translating, I think "crucifixion rack" or "cross" both sound good.
As for arbor, I think it is also valid. Some of its meanings include: - a main shaft or beam - a spindle on a cutting machine that holds the work to be cut (in this case, the "work" is Rukia). See also "mandrel" http://en.wikipedia.org/wiki/Mandrel
Looking at the manga page again, http://www.onemanga.com/Bleach/152/ , it seems only the main beam gets destroyed. Certainly Ichigo hasn't destroyed the whole of the structure. This makes me lean toward using arbor.
On the other hand, it's possible that 磔架 is used other places in the manga and maybe it does refer to the entire structure.
Got that? Listen, Ichigo!...it might be all rightI'll destroythese gallows!Wha... do... don't!That's reckless!This Soukyoku is... hey, are you listening?!
The Soukyoku is the giant cleaver that was going to be used to kill Rukia, and which Ichigo later destroyedto remain like this a bit longer...
