Proposal: Digital Fabrication
We've passed the total number of people committing --- what's needed now is another 32 or so people who have 200+ rep on other SE sites.
Alternately, how does one go about recruiting people from other SE sites?
As with all forms of advertising on stack exchange, it would be frowned on to directly promote this proposal on other stack exchange sites or their meta sites.
However if you are asking a question, answering one or participating meta discussion anyway, and the subject comes up, I see no problem in mentioning that this proposal exists in passing.
This happened a lot on Stack Overflow, when we were trying to get Programmers created, and again on Programmers, when we were trying to get Workplace created. In these cases people would say something like "This question is off topic here, but is good-subjective and would be a good fit for the proposed X site".
So, I would suggest that you hang around on sites where this proposal might be of interest (for instance Robotics or Electronics), participate fully on the site, and mention this proposal if and when the topic comes up. Be subtle about it and no-one will raise an eyebrow.
You may also want to start thinking now about possible community promotion adverts for when we get into beta. On Robotics I managed to get our adverts placed on several other sites in the network and it really helps raised awareness of a new beta site.