Monday, 18 February 2019

Arri 16St Service


Arri 16St Service







In 1937 Arnold and Richter revolutionised cinematography when they introduced the Arriflex 35, the first spinning mirror reflex camera. It was an idea that would eventually become the model upon which all professional movie cameras were based, continuing right up to the present day with Arri's top-of-the-line digital camera Alexa Studio still utilising a spinning reflex mirror for its optical viewfinder.

Building on the success of their 35mm design, Arri released the 16 St in 1952, the world's first 16mm reflex spinning mirror camera. There had been some pretty high end 16mm cameras before, notably the Cine-Kodak Special and the Movikon 16, but the Arri 16 St really elevated 16mm to a professional level, and opened the format up for news gathering and documentary work.

With its ergonomic design, pin-registered steady image and durable construction, the 16 St has become something of an icon, and many people's favourite camera of all time. Countless documentaries, music videos, shorts and feature films have been shot with this camera, including Cassavetes' Shadows, Robert Rodriguez's El Mariachi and much of Sam Raimi's Evil Dead.

Tools

It's imperative to use the right tools for working on precision machinery like the 16 St. This means using screwdrivers that are the right fit for the screw head and not burred or damaged in any way. Most of the screws are slotted, but a few require specialised drivers with two pins. You can make your own by filing down the centre of an appropriately sized slotted screwdriver, or fitting steel pins in the end of a custom machined driver. Occasionally circlip pliers are needed, or spanners. A pair of good tweezers will also be invaluable. A compartment tray to store the various tiny components is a very good idea and can help to separate the elements of each sub-assembly. I would also recommend using clear plastic containers upside down to cover fragile parts like the mirror or optics and protect them while you work. A multimeter is necessary to check microswitches or do continuity checks, and a regulated power supply handy to check current draw.

For cleaning I use compressed air, cotton buds, an old toothbrush, soft bristle brushes, cotton cloth, tissues and occasionally a brillo pad or brass brush. An ultrasonic bath is used for bearings and movement components. Kim-wipes and swabs are invaluable for cleaning delicate surfaces like viewfinder optics and the mirror. The cleaning agents I use are isopropyl alcohol, shellite (or napthal), CRC 2-26 for corrosion and a good quality lens cleaning solution like Pancro. Acetone is occasionally handy, but be careful of painted surfaces or plastics.

To properly check the camera flange focal depth a precision depth gauge and perfectly flat 16mm wide backing plate to fit in the gate are more or less indispensable. If the movement is removed, there's no other way to check this critical distance when things are reassembled (other than a collimator and a perfectly collimated test lens, but this won't allow you to check gate flatness).

Lubricants

The main recommended lubricants for the 16 St are Arri's "special grease" Isoflex LDS 18/05, a molybdenum disulphide grease called Molykote G-n paste and a relatively viscous, golden oil called Chronosynth 1/8. I generally apply grease with a good quality flat brush (one for each grease), and oil with a syringe. Arri used to supply an oil pen for applying oil to the various oil holes that are sealed with a sprung ball, but you can easily depress the ball with the wooden shaft of a cotton bud and apply the oil with a syringe instead.


Service Procedure

The first step is to check the camera over and look for obvious issues - corrosion, contamination, structural damage or signs of a drop. I check that the lid fits well, nothing seems bent, the camera manually turns over without tight spots, the pressure plate looks OK, the power cable is in good condition. Then I run the camera from a power supply set to 8.5V and check the current draw, listen to the sound of the camera, apply some drag by holding the take-up spindle. I fit the magazines and run the camera again. I check that the buckle switch is working, and that it's also activated when the sprocket roller carriage is opened. I check the turret and the mirror, and the state of the viewfinder image. The flange depth and gate flatness is measured with a depth gauge.





To begin the camera disassembly, we start with the run plunger/buckle switch module at the bottom of the film chamber. First loosen the upper screw visible inside the motor cavity that fastens the wire heading off into the body, and pull the wire free with some tweezers.












Then undo the 2 screws in the camera base and remove the assembly that houses the run plunger.






At the back of the assembly is the microswitch that cuts motor power when the buckle is tripped. If the buckle switch wasn't properly activating, check that the positioning of the various components is correct (including the set screw that holds the flat spring at the right depth), and that the microswitch itself is not faulty.












Undo the 4 screws securing the drive belt cover plate, and remove it.











Undo the 2 screws holding the right angle plate beneath the gate and remove it.













Unloop the drive belts from their spindles and undo the screws around the edge of the platine.














Leave the 4 screws between the sprocket drive and feed spindle, they hold the tacho and do not need to be removed.













Using a 2 prong driver undo the screws holding the spindles.













Note that the feed and take-up spindles have differently angled ratchets underneath, allowing them to spin freely in different directions. Mark which one is which, or make a drawing.









Now the secret trick. Peel back the lining at the top of the gate using a bit of acetone to soften the glue. Beneath it are 2 screws that need to be undone.












Now the platine can be removed, with a bit of finesse..











..to reveal the drive gearing, counters and tacho on the underside, and the movement beside the gate.












These gears drive the sprockets and counters and since they don't require precise rotation like the movement gears, they use plain bearings (shafts in bushings) lubricated with oil. The ball spring lubrication points on the chamber side feed into the tubes you can see and supply oil to every bearing.







If the sprocket rollers are not turning freely the carriage needs to be removed to be able to remove the rollers for cleaning and lubrication. There is a spring at the carriage arm pivot that hooks into holes which will need to be re-fitted for re-assembly. The spring and pivot are lightly greased.







Note the small spring at the roller carriage end which pivots in a hole and forces either one roller or the other away from the sprockets. The rollers can now be removed, the shafts and holes cleaned, and one or two drops of oil applied before reassembling.











Once the rear roller and guide plate is removed the belts can be unhooked from the sprockets and cleaned in an ultrasonic bath.












The grooves where the belts run are cleaned.













The guide can be cleaned and a drop of oil applied to the shaft for the rear roller.











When reassembling, use two film thicknesses to check all the spacings, and make sure the guide is not scraping against either sprocket. Remember to fit the belts back first!













With better access to the motor cavity, now is a good time to clean any dirt or corrosion present, especially the un-anodised strip near the locking lever. The ground voltage (negative on the battery) is conducted through the camera chassis to the motor via this strip.











Also clean any dirt or corrosion from the corresponding part of the motor body..













and the positive (+8V) contact at the front. Excessively corroded or pitted contacts can be polished with a leather strip and some jeweller's rouge.









The motor shaft end engages in this rubber socket to drive the camera. A common problem is hardening or splitting of the rubber, which can cause the motor shaft to slip inside rather than form a secure connection. I use a rubber rejuvenator to help prolong the life of the socket, but it may need replacing.






The turret should rotate smoothly and click snugly into its 3 positions. There should be no axial play, or the flange focal depth will be compromised. The releases either side of each mount should operate without sticking, and lenses should seat firmly. Some old Arri St mount lenses rotate within the mount when focussing, which can cause wear to the mounts over time. To remove the turret requires a special 2-prong driver.







Carefully remove the turret, noting the 3 spring rollers. They should compress smoothly into their holes.














The view under the turret, revealing the mirror.













I clean the old grease from the edge of the turret cavity. On reassembly I grease it lightly with a honey textured grease recommended by Arri called Catenera KSB, but any relatively viscous dampening grease would probably do.








To remove the movement/mirror assembly we need to remove this support bracket, held by 2 screws.














Then remove the 2 screws inside the turret cavity..













and carefully remove the assembly from the back.












Note any shimming material where the assembly seats (see the silver shims in this example). This is determining the crucial focal flange depth.













A view of the assembly showing the movement.














After opening the hinged pressure plate I check the side rail spring to make sure it moves freely. Note the prism at top that diverts an image to the viewfinder.











The mirror/shutter and ground glass assembly removed. During a movement disassembly any shims or spacers need to be carefully noted. I actually wouldn't recommend going this far without some experience and proper tools.










The movement/mirror driveshaft removed.














The gate removed.















Disassembling the movement.














The various parts after some have had ultrasonic cleaning.













Lubricating the claw cam follower..















its pivot shaft..













and the cam.














After reassembly.














The mirror/shutter refitted.















The pulldown claw and registration pin alignments checked with a steel film gauge.












Cleaning the optic in front of the viewfinder prism with a swab and isopropyl alcohol.











Once fully cleaned, lubricated and assembled, the movement/mirror assembly is carefully refitted, making sure the shims are in place. After the turret has been refitted a calibrated 52.00mm depth gauge is used with a steel backing plate in the gate to exactly measure the focal flange depth and flatness, from lens mount to film plane. If it needs adjusting new shims are cut and fitted.






The ground glass is under the eyepiece, and its depth is set by screwing the viewfinder tube in and out. To do so a set screw inside the door needs to be undone. A calibrated spacer at the back allows the tube to be screwed home to the correct distance. The ground glass is then aligned to the horizontal and locked by its lock ring. The ground glass should show a sharp image when a calibrated test lens is focussed on a test chart.






After reassembly, fresh film is run through the camera to check for scratching and smooth transport of the film. The basic camera functions are tested, the current draw is checked, and any magazines are checked for take-up tension and smooth function.



6 comments:

  1. Hi Dom,
    Does the movement timing require fine adjustment upon reassembly or is it only a matter of getting the gear teeth back in proper sync?

    Aloha,
    Mark

    ReplyDelete
  2. Thank you very much! Very interesting.

    Do you think, you could make a service-manual for Beaulieu 2x8mm cameras in next time? That would be great!

    ReplyDelete
  3. Thank you!! Your blogs are phenomenal! I've been searching for some instructions on how to disassemble Schneider Kreuznach lenses for internal cleaning - just as a suggestion.
    Once more Thank You!

    ReplyDelete
  4. Hello from North West London. This is my very first post. This is a question that has troubled me for many years regarding my two 16S/B cameras and my 16BL. How does the pulldown claw and the registration pin work when the camera is run in reverse? While I'm here may I ask ask a second question? I have a 12V torque motor, not sure if it's a factory version or converted from an 8V. Is it safe to put 12V through the camera and motor or does the camera need some extra form of protection from the over-voltage? I read that the 8V torque motors could be easily damaged if run off a 12V source. I'd appreciate any advice regarding the use of 12V versus 8V. I should add that both of my cameras are high 18000 plus serial numbers and in in fine condition. Thank you all in advance. Paul Cotsen

    ReplyDelete
  5. Hello,many many thanks for this masterful lesson: I hope to see some more of them!Best regards - Maxwell

    ReplyDelete
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