Should grad students also serve as lab managers? I'm a 3rd year PhD student in a robotics lab. My advisor recently moved universities, so our new lab space doesn't have a large stockpile of supplies and equipment. As the person who does the most hardware-based stuff in the lab, I've been slowly acquiring necessary equipment and supplies for electronics work, mechanical assembly, etc, with the support of my advisor. 

There most senior student in the lab is now trying to convince me to take on the role of lab manager. He indicated that in his past labs there have been graduate students who also are given the (extra, unpaid) role of lab manager. He keeps joking (?) that he will volunteer me for the position to our advisor.

It takes a lot of time to spec equipment, make purchase orders, organize tools efficiently, etc, and all the other students in the lab come to me when they need help with anything from university logistics to help using equipment. The equipment is necessary for my work, and I'm  happy to help fellow students, but it's starting to take way too much time away from my work, and I certainly don't want a formal position that necessitates this responsibility. I'm giving a conference talk next week and will miss our regular lab meeting, and I'm worried that this other student will volunteer me for this position when I'm not there.

Is a PhD student also serving as an (unpaid, but official) lab manager a typical arrangement? I've never seen it in any of the labs I've worked with or observed. Research is my absolute top priority and I don't think it's useful for a PhD student to do the work of a lab manager because we're there to do research. If I do get volunteered for the "position" without my consent, will my advisor think I am an unmotivated student if I politely decline?
A couple thoughts, on someone who has been now a grad student, a lab manager, and a PI:


Someone has to deal with those things, and the PI is often not the best person for that particular role. And it tends to be helpful if there's a single point of contact for things like "Have we ordered more X?". I find that "It's everyone's problem" turns into it being no one's problem.
A lab that will volunteer you for something while you're not there, the PI can't gauge your workload, etc. is not a lab I'd be enthusiastic about working in long term.
Working as a lab manager is a helpful entry on your CV, especially if you don't necessarily want to be a PI. There are often questions on this site about research careers that aren't TT faculty positions. Lab managers are one of those positions, and having experience with it etc. is a good thing.
It's also a good thing if you are interested in being a PI. Because from experience, when your lab is N = 1 people and you're just setting things up, knowing how all of that works is handy.
"...we're there to do research." And how will you do that without the equipment necessary for your work?


That being said, in an ideal world I wouldn't want a graduate student as my lab manager, because graduate students are inherently transient, and one of the values of a lab manager is as an inter-generational knowledge base. But maintaining a full-time, permanent position for essentially a staff scientist is often out of reach of even fairly well-funded labs.