I like it. The repitition makes it sound like a chant, which is good. One thing i would say is that because it's arranged into pairs (i.e. new line and then repeating line), it would look and sound better if you added a 'The big guns never tire' to the end of the first stanza and a 'The forge worlds never tire' to the end of the second. As it is, there's an uneven number of lines which seems odd in a work using repetition. Also, another piece of advice; if you want two lines to rhyme, it's best to have the same syllable length in both of them. Not necessarily the case, and many great poems don't do this, but often mismatched syllables makes for odd rhythm even though the end words rhyme. For example
Oil the gears of the great machine
1 2 3 4 5 6 7 8
We labour on, unseen,
1 2 3 4 5 6
The top has a full 2 syllables more than the bottom leaving the lines sounding mismatched. Although the lines 'rhyme' in last word, it makes it difficult to read them rhyming because they run at different paces. I might suggest
'Oil the gears of the great machine
The forge worlds never tire
We labour on ever unseen,
The forge worlds never tire'
And by asdding that two syllable word you do wonders to improve the rhythm. Remeber, it's not just rhyming words, like music (and i say this also as a (somewhat underpracticed) bassist) poetry has to have a rhythm; so many beats per bar etc... You can vary the tempo and time signature of the music but not 'per bar' because otherwise it sounds mismatched. The same goes for poetry. If you look at Keats, or Vaughn (my personal favourite), they don't give every line of their work the same amount of syllables, but they balance the rhythm of each stanza brilliantly (which is what makes them such geniuses).
Anyway, as i say, it's not a 'hard and fast' rule and you don't have to follow it, but if you're struggling to get a decent rhythm, the easiest way is to just use the same number of syllables on the lines you want to make form a rhythm, and then you needn't worry about more complex structure.
Anyway, I hope you don't take this the wrong way, I don't wish to discourage you at all, and I like the basic premise of the poem; I just thought i'd give a couple of pointers as to how you can 'polish it up' a bit.