Lets polish some old thread up to match current version 
Was gonna type some sick post but it became too huge, so much to say about the topic, gotta pull a guide out of it 
I'm just gonna post couple of setups related to the recent versions of FS, cause of changes of repairfactory/repairunit powerbuildrates and tinker being not able to lumbermill anymore.
This for example, is a slighly modded version from Englos setup, which used to have 2 factories at the bottom, half a space below the middle repair unit. I like the 2 mills setup, where builder can always keep building from the same spot, you can also make the setup up faster that for the width of 4 mills for example. Plan is to use shift+build to "prebuild" 2 mills and singletransmute 1st right when it's ready and use shift+build on its place and keep doing that like forever 
tiny_mod.jpg 214.84KB
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This tiny setup is incredible powerfull, it can pop up a mill every 3,84s (12 in 46,12s). Forgot to make advanced factories to the top. But even all factories as normals, it does 3,98s/mill (12 in 47,74s).
Lets check some math here:
Buildtime of mill (with rate of 1,0) = 35s
Survivor buildrate 1,0 (even editor says otherwise)
repairunit lvl 6 rate 0,85
repairfactory rate 0,5
Using repairunits and repairfactories as above
realBuildTime_1 = buildTime / totalRate = 35s / (1,0+8x0,85+4x0,5) = 35s / 9,8 = 3,57s.
Same with ONLY repairfactories:
realBuildTime_2 = 35s / (1,0+12x0,5) = 35s / 7 = 5s.
So, by using both units and factories right, you can speed up millproduction quite a bit, with this example showing +40% boost, for example 200 mills vs 280 mills, huge right? 
And then some funny overkill setup, using another unit to speed up and maxed out repair units as well, this isn't viable in real game but just as a testcase 
2_mill_opposite.jpg 224.16KB
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- 8 repairunits + 3 repairfactories + survivor + mechanic + 2 x hovering repairbots + 2 x constructed repairbots for each of 2 mills.
- Just noticed, I COULD had use advanced repairfactories too, but on the other had, alchemist unit couldn't keep up for a long time because of cooldown on manapots, haha
So, probably alchemist hero would be needed anyways
- It spits out a mill EVERY 2,948 seconds 
- 21% faster than the previous faster setup and 70% faster than the factories-only -setup 
Some other setups
wallbuildsetup.jpg 225.54KB
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diagonal_optimized.jpg 269.32KB
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fast_lumbering_setup.jpg 193.8KB
0 downloads (Tinker cant powerbuild atm, just got to know)
another.jpg 208.69KB
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2_build_formation1.jpg 199.52KB
0 downloads (Mechanic can
)