NFTS short film prop

National Film & Television School short film - untitled work, Oct 2003

A small job recently completed to make a working trap door, with top and bottom rack and pinion action. The dimensions were an exact requirement as it had to fit into the rest of the set, which was produced at the NFTS.

This is a CGI sketch of the piece, which was a great help in addition to the dimensions.

Here's a..... well, I don't really know what it would be, but it wasn't mine! I think they just wanted to see if they could get it to work....

Here's what I came up with. It's dimensionally correct, and it also works. The secret with a straight cog and ratchet is in realising that the mesh point is about 64% of the way up the teeth, and not just at the tips.

I also increased the number of teeth from 6 to 12 so that the acTion would be smoother.

These two pictures are identical apart from the position of the locking bars. The top is locked and the bottom is unlocked with the angle of the handle giving it away.

Theres a duplicate mechanism on the bottom, of course.

Note the 1cm x 1cm scale on the bottom.

Making it is one thing, but getting it from Edinburgh to London was another. To save on postage and minimise damage, I made it into a flat-pack kit by using dowels and biscuits and providing an assembly plan.

Here it is in the set....

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