How does the platter work.

[Allan Broadfield]

As a projectionist from way back, in the days before platters, I have often wondered about these wonderful gadgets that I missed working with.
Call me simple, but how does the module that separates and supplies the film from the centre of the platter work without damaging or scratching the film stock?
A diagram illustrating this would be great!

[Steve Lee]

Hi Allan,
I will have a go at trying to explain how it works.

On the platter that is feeding the film to the projector, the film leader is in the centre of the hub rather than playing the film off a spool where it on the outside.
There is a removable section that sits inside the centre of the film that is nicknamed the brain.




When this is placed onto the centre of the platter table, it make all of the electrical contacts to control that particular platter.
The film is threaded through an arm that has film guides on it. This arm is connected to a potentiometer that controls the speed that the platter turns. If the platter is turning to slow the arm will swing to the left, and this will speed up the motor. The same goes if it is running to fast, the arm will swing to the right, slowing down the motor.
Also in this section there are several rollers that slightly angled, this allows the film to be lifted up over the platter onto a pickup roller on the main frame of the platter system.



On the main body of the platter system there is a sets of rollers, in which the film is threaded up and down before it heads off to the projector. This is an emergency shutdown system.
If the film gets to tight, it will lift the bottom roller up and this will shutdown both the projector and platter.

Once the film has left the projector if is feed back to the platter with a series of rollers. Underneath each of the platter tables there is a large arm that has a roller at the end of it.
As soon as the arm moves back towards the main body, there is a point where it will start up the moter on the takeup. This will hold constant tention so the the film will never snag on startup. This arm also controls the speed of the takeup.



On the table that the film is being taken up on you place a center hub. This has a locking clip on it. This sits on the platter and is held in place with a couple of pegs. When this is in place you lock the clip on it. This expands the diameter of the hub by a fraction.
Without this function you would never be able to remove the hub from the center of the film, when releasing the clip the hub shrinks back to a smaller diameter and allows it to be lifted out.

Over the years I have used many platters from all manufacturers. As long as they are set up correctly, they are a wonderful way to show a film. With no rewinding needed between shows, they are also very kind to film compared to running a feature on spools.

[Graham Ritchie]

Used them for 10 years as mentioned properly set up they are brilliant to use. The 5 deck one in the video I took, I now use at home, long films films like Dances With Wolves is perfect for platter use.

[Allan Broadfield]

Thanks Steve for that informative post, I'm sort of getting the idea how the module, or 'brain' works. What a diff from all those change overs and rewinding we had to do previously.
Also what a sad ending, to your film, Graham. I haven't been involved in closing down a cinema, but I've shut down a couple of laboratories, (not personally!) One when it was bought out and the other when digital took hold. Visiting the shell of the building a few months later and seeing my notes still on the walls was very sad.
I must sound pretty ancient, but a friend, now deceased, could hark back to the day when sound equipment was wheeled into his box for the first time!
Incidentaly he claimed that the Vitaphone disc initially gave better quality sound than optical which came later, and you couldn't argue with him!

[Steve Lee]

I would like to apologize for the spelling mistakes, the joys of typing English on a AZERTY keyboard.

There are some points I forgot to mention.

When the film is being taken off the platter, although it is being pulled by the projector, it is not actually being pulled with any great tension. The platter will feed the film into the brain by controlling the speed that the platter rotates. When set up correctly the inner loop of the film will enter the guild rollers on the brain at a curved right angle, so it's not actually dragging it. The rollers around the outside of the brain module are only there for an emergency. The film only comes into contact with them when you lace up the system. As you can pull the film faster by hand than the projector, this will send the platter into turbo mode, wrapping the film around these rollers until it stabilizes its self.

Each of the platters are independent from each other, and can be used to feed or take up the film. They were produced up to five tiers high like Grahams one, so it was possible to run two films simultaneously off of one system.

Being independent from each other, if you were in the situation where you need to move the film into a different projection room, you could take the film up from the projector onto a spool, rather than sending it back to the platter, and vice versa.

The platters each have a rim drive motor that can be disengaged. By doing so this allows the platter to be turned by hand, and will allow it to go backwards. This is how it is possible to make up or plate off a film too or from a spool or bobbin. These units came with a makeup table trolley, that had a small motorised platter on it. These plugged directly into the main unit, and allowed you to control the platter from the trolley.

The only drawback with them, is when there is a problem with the film print, as you have no instant access to the problem.
I worked with someone who insisted they made up the films every week. How, with a blindfold I think. I could guarantee that there would be at least one rack line out in every print. This meant I had to pull the entire print off of the platter to find the reel change, re splice it back in rack, and then plate the film back onto the platter between screenings. If I was lucky I had ten minutes to do so.

Only looking back now it was great fun but incredibly stressful to do, especially when time was not on your side. As it would have a knock on effect for all of the screens for the rest of the days screenings.

[Ken Finch]

Fascinating. An excellent explanation Steve. I have seen them in operation at C. T . A. visits to cinemas but have never been a professional projectionist. Once visited a multiplex with a large number of screens where the same film was being shown in 2 screens from what appeared to be from the same platter. Thought the film would pick up a lot of dust on route. Just one projectionist in charge of about 10 screens!