ISCG Tab offset, now in 3D!

[Crowemagnon]

Im building a big enduro bike after riding a Yeti SB5.5 for the last six months, and a 140mm steel bike built around the switch-Infinity for the six months before that, and deciding more bike is the answer. I'd like to add ISCG'05 tabs giving me the chance to run a chain-guide or big old bash-guard without the use of an adapter (i think... see later). also, i think having something there to keep the chain riding too far inboard (if it falls of the inside of the ring) that it doesn't try and get in-between the swingarm and the bbshell/frame might be good, but thats fairly situational and maybe a discussion for another time.

the ISCG'05 standard, is, ultimately from 05, and now im struggling with it. i'd (respectfully, i know who's here ) like to think things have moved on a little...

looking at the BB from the drive side, i know where the three M6x1 holes go in 2 dimensions ( plenty of documentation of this online) good work internet. i dont know where the useful face of them sits relative to the bike centreline, or the chainline, or the bb face or however you want to define it in the third dimension.

In trying to figure out what offset i'm going for; i can only find really old references to this from some weird compatability documents for old blackspire chain guides that i'm not entirely (read, at all) confident about.

it'll use a Boost rear end, and run a boost chain-line upfront (though its never given me any trouble not to...? ) (likely on sram GXP or bb30 cranks, using a direct mount oval ring with the correct offset)

the bike has a 73mm BSA threaded BB shell so will use an external type BB, like a screw in GXP, or a 'BSA30' from someone who doesn't have a proprietary tool.

am i really bad at google, or is there a firm standard here? what is it? does it reference chainline or bike centreline, or cassette position and why?

i think i want to do as little "spacing out" (haha) as possible, to keep the thing i bolt to the tabs sturdy (spacers feels like adapters on a torque wrench causing cam out but in brutal rock strike to the BB form).

im hesitant but potentially open to the possibility of this not being the best idea, and having a less sturdy connection act as a 'fuse' or to allow something to work better, but i'll take some pretty serious convincing.

thoughts? facts? fake news?

[Crowemagnon]

because this post has stacks of key words relating to the main question, anyone who is looking for this answer will likely end up here, so for those people, and other general information on the ISCG05 standards, theres a really good document that will download from the following link. its just that the offsets in the drawings are cropped off the page...

https://www.google.com/url?sa=t&rct=...T5ia52KT6fGlPb

[Crowemagnon]

right.

to no avail i've continued to look fora couple of weeks.

the frames i see rage from zero offset, through a tiny offset, as little 0.7mm (which seems to be just enough leave paint on a flat tab when facing the bb shell) right uptoaround 7mm.

im going to test fit a few cranksets and see how things lookwitha boost chainlike and report back.