I am bringing a Mitchell S35R (or Mark II...) back to life for a short test: all seems to work perfectly except for the take-up friction, which is pulling the film way too hard. Loosening the set screw didn't solve the problem: a sort of all or nothing effect. So I have cleaned the discs which were indeed really dirty. Now my question is: should I oil or grease these discs? I hope somebody can help... (and yes I know, the best for this camera would be to have it properly serviced, but that is out of the question for now, and here, in the Netherlands...)
Mitchell S35R / Mark II take-up friction
Posted 07 June 2016 - 09:15 AM
I'm sure you will get a better answer, but my guess is grease, because oil could splash onto film. So what you cleaned off was probably congealed grease. I recently stripped down a Steenbeck and the grease had turned into a flexible toffee-like solid.
What sort of grease I have no idea. I used a general-purpose lithium automotive grease, not a high-temperature type. If it's for your own use you could use what you like-you can always remove it afterwards.
Edited by Mark Dunn, 07 June 2016 - 09:19 AM.
Posted 08 June 2016 - 01:35 AM
Thanks Mark, I thought the same. However since I don't know which material the central discs are made of (black plastic-like) I am hesitating.
Posted 08 June 2016 - 04:11 AM
On the feed sides of the magazines there are brakes indeed. For the take-up there is an adjustable friction built into the camera itself: it's a gear between two discs. This brings me to another question I only thought of now: the belt driving the magazine isn't supposed to slip is it? The old leather belts with the camera are shrunken and unusable, so I made new ones from 3mm diameter "ropanyl" (the green stuff you can weld yourself for every size of belt). This material is definitely not slipping easily.
Posted 08 June 2016 - 04:16 AM
I know nothing specific, of course, but I'm thinking that a film takeup needs some sort of clutch arrangement to allow for the increasing radius of the roll.
So perhaps you're right. A fresh leather belt would slip. Maybe you need some thongs. IIRC the Arri 2C uses leather belts for takeup.
The plastic could be some variation on Bakelite. The camera may be old enough.
Edited by Mark Dunn, 08 June 2016 - 04:22 AM.
Posted 08 June 2016 - 08:04 AM
Posted 08 June 2016 - 08:24 AM
A gear may transmit the drive to a magazine, but there has to be a means, after the gear in the drive train, to allow slipage on a takeup system. One can assume a friction disk or belt. Yes?
Posted 08 June 2016 - 09:27 AM
Mark, yes, the discs could well be bakelite, they look like it, this camera is from the late '60-s I guess.
Gregg, exactly, and in this case one of the gears is not fixed on its shaft, instead it is between 2 friction discs which are connected to that shaft. A spring presses this assembly together, you can adjust this pressure with a thumbscrew.
I am not familiar with the older Mitchells (wouldn't mind to correct that though...;-) but since the magazines are interchangeable between the S35R and the older models I guess the way the slipage works should be the same.
Posted 08 June 2016 - 10:46 AM
Riddle me this, when you cleaned the disks, during re-assembly, did you accidentally squish the assembly too much? It does require some sort of gap.
Also, shouldn't there be some sort of "slip" material in those disks that MAYBE wore away?
Posted 08 June 2016 - 02:36 PM
Tyler, after re-assembly, I started with much lower pressure on the assembly than it was set to, but that does not guarantee that there was not something wrong of course. When you set the pressure really low those discs still come apart( you can see the side of the assembly when you open the door for the "inverted" 400 ft. magazine at the back of the camera). And yes, I hope not, but it could very well be that too much material wore away. At least not to the surface of the 3 metal pins with which each black disc is attached to the side of the gear...