Originally posted by DarthTanyon:

who needs this farm? Like.. 5 dungeons gets you all the cores you'll ever need and then coal? Take like 2 minutes to cut down 5 trees which will last you days and days..

I guess that depends on how many portals one feels the need to make, and/or how many smelters are required to provide the desired amount of metal at a speed that makes one happy.

Originally posted by yai200439:

Originally posted by umop-apisdn:

Remove the stone blocks; as I understand it, spawners cannot spawn mobs on top of player-created structures.

Was there a change in Surtling spawning mechanism? Because there are many youtube showing spawners working fine with stone blocks

I was not aware of that; thank you for the information. My apologies for my inaccurate statements.

Originally posted by Draconifors:

Originally posted by umop-apisdn:

Spawners don't care about workbenches, campfires, etc.

According to the wiki, fire geysers are not spawners; they are spawn points, and as such suppressed by workbenches.
I once placed a workbench right next to every one of a bunch of surtling spawners, and nothing ever spawned.

Noted; again, thank you for the information.

TL;DR: Aye, it would seem the workbenches are the problem.