Fitting acrylic disc in tube

I want to build a replica plutonium canister from Back To The Future, and I have a question about fitting acrylic discs inside a tube.
I have acces to a Trotec laser cutter. If my tube has an 80 mm internal diameter, should I cut my discs a bit smaller (79.9 mm for example) or should I just cut them to 80 mm? I don't want to waste any material experimenting.

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I would cut them 80mm or more, as the kerf of the laser will remove some plastic. So if you draw them as 80mm in the software you use, they will actually come out smaller. You may be able to find out the kerf of the laser online and work out what size you need from there.

If you are not able to speak with someone who has used that particular laser cutter to find out what its kerf is, you must do a test cut or two. Cut a small square from the material and then measure it with a caliper to determine the kerf, and adjust the diameter of your discs appropriately. Don't forget to measure the tube inner diameter as well as that will not be exact to the listed size.

If you cut the square in the area that would be excess material between the circles you won't be wasting anything.

Ok, thank you very much for the help!

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EyeballsStudio said:

I want to build a replica plutonium canister from Back To The Future, ...

Click to expand...

Screen accurate or not?

The rod itself should be as accurate as possible. The canister won't have a rotating bottom that allows the rod to fall through. If this version turns out fine, I'll try to figure out how to do that.

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Hi EyeballsStudio,

Don't know if you will find this useful or not, if you decide to build a HERO (rotating bottom) or a stunt:

I see from this video that there where at the very least 12 canisters made for the production plus the HERO.
https://www.youtube.com/watch?v=f2c-tMZSZtY

I am wondering if 11 of them are only STUNT versions?
There would be no reason to remove them from the case during filming, so they could just be "place setters" in the case.
They might not even have liquid in them....

The one he takes from the case (and in one shot), he shows that it contains liquid, but it wouldn't necessarily need to have
the rotating piece at the bottom with the larger beveled hole (this larger hole is so it can be captured by a slightly raised,
thin wall tube inside the chamber).

This "escape hole set up and rotating bottom" would only need to be on the HERO version.

Since there was a break in the scene, we saw that the canister (sitting next to the reactor) was already sitting there while the reactor cover was being removed (and it may not even be the one taken directly from the case).

He then picked that one up (the HERO version) and placed it into the chamber and twisted it.

When he placed the HERO canister into the chamber, he had to aligned the larger, beveled hole (drilled into a smaller diameter "disc", loose twist bottom)
with a "slightly raised, thin wall tube" (down inside the chamber), which would then hold it in place while turning.

So when the canister was rotated, this bottom cap never moved and the inner 1-1/4" tube came around to line up
with the beveled hole, allowing the 3/4" plutonium rod to fall straight through.

So, I think some of the close up pictures I've seen are showing the stunt versions (without all the details of the HERO version).
There may have been 3 versions, stunts, closeup and HERO ?

These are just my observations on how it may have been done ....
I hope this helps a little.


propmaster2000
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EyeballsStudio said:

The rod itself should be as accurate as possible. The canister won't have a rotating bottom that allows the rod to fall through. If this version turns out fine, I'll try to figure out how to do that.

Click to expand...

If you decide to build a working canister maybe this might give you something to think about.
Just speculation: