How are oscillating bearings in film camera movements usually designed?

[Geffen Avraham]

Hello.

I've been looking into film camera movement design lately, and am trying to learn specifically about how different manufacturers approached oscillating bearings. To understand what I mean, take a look at this animation of Geoff Williamson's VistaVision movement.

As you can see, the upper two bearings, blue and white, are attached to the round cams. They complete full rotations.

In contrast, the lower two bearings, gray and orange, are attached to the claw arm. They never complete a full rotation, and instead oscillate.

 

I have heard that ball bearings are a poor choice for oscillating applications, since the balls will irregularly rub against their races and potentially introduce instability or false brinelling, but some mechanical engineers have said they work fine despite this.

I believe the old Mitchell cameras used metal bushings with metal pins, but whether it was steel-on-steel or bronze, I have not been able to find out. Presumably, these bushings required frequent lubrication.

One advantage of more modern camera movements, such as an Arri or Aaton is the lack of necessity to constantly oil the movement.

But from looking at pictures of Arricam movements being assembled, it seems like they may in fact use ball bearings for the oscillating element after all! That being said, I have not been able to find a higher resolution than this, and have never serviced an Arricam. I am hoping someone with experience can enlighten me. Do Arricams use a ball bearing here?

 

In the Aaton movement, which appears to be permanently greased, there is some form of bushing system, but I am not able to find any more information about what these bushings are made of. These bushings are also vertically constrained by a thrust washer and an e-clip, but I am extremely curious to find out whether they are preloaded (and if so how much) or allowed to float freely.

I realize these are extremely niche and technical questions, but hopefully someone here with servicing experience can help like @Dom Jaeger, @Simon Wyss, @Steve Switaj, @Tyler Purcell

[Tyler Purcell]

The arricam movements are very similar to the moviecam's and they're all plain bearing. Bronze is commonly used for the main through shaft. Then everything else is metal on metal with lubrication and very fine fitments. I have a few busted 535 movements that we have apart, both from dropped cameras. You're welcome to examine them along with all the Aaton movements we have. Come down sometime and we can chat. 

[Geffen Avraham]

Thank you!

Why doesn't it look like there are any visible bronze elements in the picture I linked? Also, I was under the impression that Arricams do not need to be oiled every 1000 feet like a Mitchell, is that accurate?

[Tyler Purcell]

Arricam's are like 100k ft between lubrication. 

The bronze elements are just blocked, you can't see them from the outside. 

[Geffen Avraham]

Having checked again, it appears this picture is actually an Arri 435, not an Arricam as I originally thought. How similar are they?

[Steve Switaj]

14 hours ago, Geffen Avraham said:

Having checked again, it appears this picture is actually an Arri 435, not an Arricam as I originally thought. How similar are they?

Geffen:

In another thread we were talking about an old article in a 1990 SMPTE journal where Arri talked about designing their 765. They went into a lot of detail about the pulldown claw.

Gergo G found the document online and posted a link https://cinematography.com/index.php?/profile/100761-gergo-gosztolya/

This looks like the same basic strategy. In the article Arri specifically talked about ball bearings on those two linkages.

[Steve Switaj]

I went through several Mitchells. All the sliding parts in a GC or standard seem to be steel-on-steel. The parts don't look to be plated with anything weird, but the outside sleeves have some coloration that could indicate heat-treat then grind to size.

the NC (and by extension some of the derived Panavision movements) seem to have one link that oscillates at one end and has a bearing on the other.  In the camera I looked at it looks like the oscillating end is a simple pin in hardened bushing, as is the rotating bearing.

There are several ball bearings supporting various shafts, but the actual movements are heavy on precision ground parts sliding on each other.

If you're an old Mitchell guy (raises hand) you have heard enough horror stories that you just run these cameras very wet.