That title sounds awful!

I get on really well with my sup. In the last 7 months I've rarely had any probs with him regarding my work or direction of research etc.

However my chapter 2 is a bit of an interdisplinary effort into a field that I have never read about before. Its not his field neither so I'm thinking of contacting one of the profs from that specific department in my uni.

Should I suggest this (in a nice way) to my sup? Or just go ahead? Or how would the otehr prof take it.

I've just been writing over the summer without being in contact with my sup and wondering if I'm writing anything worthwhile (especially after reading the thread were the guy/gal had problems in their viva - its freaked me out)

From my perspective I don't see anything wrong with going to people in other departments for advice. It's your research after all. I've done it plenty of times when my research has expanded beyond the scope of practice of my supervisors. It's the way the cookie crumbles. I suppose if you do have a tetchy supervisor then it would be tactful to tacitly suggest it first and see what he says. The way I see it, you're training to be an independent researcher and you're using your initiative.

There's nothing wrong with seeking advice from others but a little professional courtesy can go a long way so I would probably raise it diplomatically with your supervisor first. You have a good relationship with your sup therefore it's unlikely he will object and so two things come out of it - you get what you want and the relationship is maintained. You will have still maintained your autonomy and independance because you raised the suggestion not the sup. Your supervisor will be aware that you need this other person's help because his expertise does not stetch that far but he will appreciate that you respect him enough to run your idea by him.

It seems perfectly reasonable to me. In fact, having the opportunity to consult an expert in the area and failing to do so, would (IMO) demonstrate a lack of initiative. I would suggest it first though - simply because there's no reason why you shouldn't, and if he is a little delicate about such things (though I can't think of a valid reason for it) you want to avoid appearing as though you're 'going behind his back' so to speak. Don't make a big deal about it though (i.e. don't be apologetic); try not to make it appear like an unreasonable suggestion with attempts to cushion it.

I certainly can't see that there is anything wrong with contacting someone else for advice in their specific area, I've done it quite a few times, the first couple of times with a specific shove from my supervisor - he's even taken me off to meet profs in other unis to discuss things with them. If he hasn't suggested it yet (and maybe he's waiting to see if you will) then I'd run it by him, there are plenty of ways to approach it especially as the chapter is interdisplinary, you can put it that you feel it would really help you to understand it from the side of someone in that field - then no offence could be taken whatsoever. The other prof would, in my experience, be very helpful and happy to talk with you and it extends your network - win win :-)

I also think there's no issue in approaching someone else for advice. My phd has two main parts, and my supervisor is an expert in one of them, but does not know the other area of research at all. I'm just at the end of my first year of the phd. I just recently met with an expert at another uni in the other area of research, and it was really helpful - she gave me a lot of advice, and pointed me in a few directions I should look at. I honestly wish I had spoken to someone a lot earlier, because it turns out that side of my phd isn't as good as it could be, and i've got a lot of work to do now to try and rectify that and make the rest of my phd something that will really stand up in that field of research.

I think you can just go ahead and set up a meeting with this person, but I would let your supervisor know that you are going to speak to them, especially as they're in the same dept. Your supervisor shouldn't mind, and will probably be glad that you're taking the initiative to address this part of your phd.