
Cinemeccanica cakestand
This is a cakestand. Not the sort that the Women's Institute would recognise, of course, it’s a piece of projection equipment.
When I was a penniless student oaf I was technical officer of Union Films, the multiple award winning student film society of Southampton University. I was a projectionist, too, of course, and specialised in showing very long films. I think the longest I ever showed was 11 reels, but I could be wrong. The Color Purple sticks in my mind as one of the longer ones, and Kelly's Heroes as the one form which the most souvenir frames had been taken by previous exhibitors…
A standard feature would be maybe five reels (2000′ per reel of 35mm film, 18″ per second, around 22 min per reel). There are a couple of ways of handling this: the classic way is to have two projectors running the film from top to bottom, and to switch projectors at the end of each reel. That’s what the white flashing cue marks are for at the top right of the screen every 20 minutes or so.

A Cinemeccanica V5, I have driven one of these. Two, in fact.
Obviously that’s a lot of projector switching, with potential for mistakes, and a lot of handling. One way of mitigating that is to join three 2000′ reels onto a single 6000′ reel, as with the picture of the Cinemeccanica V5 at right, so there’s only one change per film (or more for long ones).
But the second option, colloquially termed the cakestand, fixes three problems at once: it removes the need to switch for all but the very longest films, and it removes the need to rewind, and it also removes the need to keep two projectors focussed.
The film is spooled as usual (spooling is checking for broken sprocket holes and other imperfections that might cause the film to break in the projector), joined onto 6000′ reels then wound onto the horizontal platters. These can take over a dozen 2000′ reels, 8km of film or 17,500s (4.8h) of playing time – enough for the most self-indulgent epic.
Once you’ve wound the film onto the platter you remove the centre ring and put the payout arm in place. This takes film off the inside of the spool while the platter is driven by a motor. If the platter runs too fast the payout arm is pulled clockwise and the controller senses this and speeds the motor up – and the reverse if the platter is running too slowly.
The film is then run across to the projector (only one needed though most theatres will still have two in place) and run through the gate in the usual way. It’s then taken from the bottom of the projector and run back to another platter on the stand, which is also motor driven so takes up the film as it plays.

Film on cakestand
The result is a continuous run of film with no reel changes. You can even run the film from one projector to another and show it twice more or less concurrently (the Odious at St. Albans used to do this for popular films, I’m told).
So there you go, I hope you found that interesting. There’s some more arcana of projection I can share when I’ve found suitable pictures of things like anamorphs. It was quite engrossing at the time.