PhD supervisor will not read draft I just wanted to get some input from the community about an issue I have run into with my main PhD supervisor.

I started my PhD about two years ago (hard science field), and about six months ago I finished a preliminary draft for most my first article. The draft is about 70 % complete, but I can't write the last part yet because I am still waiting on some final results.

I sent the draft to my main supervisor as I wanted to get some feedback on the parts I had written so far. Just before summer I had a meeting with my supervisor, and it turned out that my supervisor had not read anything in the draft even though I had sent it several weeks before. As such, I felt that the meeting was rather unproductive as I basically had to spend the short time I had allocated explaining what I had actually done research-wise instead of getting feedback on my draft. This also disappointed me a little bit as my supervisor had specifically informed me before that it was preferable that I summarized my findings in article-form instead of just sending random updates whenever I had some progress.

Fast forward until now. This semester I have spent working at another institution, and my supervisor recently came to visit me. Several weeks before this I had informed my supervisor that I would like to discuss my paper draft, and was told that this should not be a problem. However, it turned out yet again that my supervisor had not read antyhing. Instead I was told that as some of my co-supervisors had taken a look at the draft and said it needed a better focus and a thorough rewrite (which I fully expected anyways), there was no need for my main supervisor to read it. However, although my co-advisors have given me good tips on some of the issues in the draft, I still feel like I have not received proper guidance in how I can restructure the entire focus of the article based on my current findings. 

As I have spent a lot of time writing this draft, and would like to receive feedback from my main supervisor on how to improve the paper, I find it disappointing that my supervisor has shown so little interest in reading my draft. It is my understanding that reading drafts is one of the main duties of a supervisor. I am now at the stage of my PhD where I can do most of the research independently, but I still feel I need input on my writing.

Is this something I should be more firm about with my supervisor? We have had a very good working relationship so far, but this issue is really starting to bother me. If anyone has any tips on how I can deal with this, then i would greatly appreciate it!
This sounds like a case of your supervisor being too busy and pushing work they consider less essential to the background. I'd suggest that, since you have alternate sources of feedback here, that you explore those and just push on toward the end. 

I think it would be harder to avoid something you represent as a "complete" draft or a "final" draft. At that point I hope the supervisor moves your work up to the first level of importance. 

Even feedback from a third party might be valuable if you can find a way to get it. 

But there is no reason for you to stall your own progress. But trying to force someone to do something they don't see as essential in the moment doesn't sound like a plan for success. Especially when they have the power.