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A vacuum to hold down a build stage offers the possibility of using very thin films to build prints on; this film can be sacrificial if cheap enough.
I have done some early trials with a vacuum table that I have fitted to my Delta printer and first tests have been very encouraging. I put a video on YouTube showing a rapid print change https://www.youtube.com/watch?v=cBisjaN8YK0
In this case the build surface was Laser Overhead Transparency film and the print material was PLA but this was not much good with ABS. An interesting result came with using the film from a Document Lamination Pouch, the inner surface is a kind of hot-melt glue and this prove an excellent surface on an unheated bed with PLA and even gave encouraging results with a warp prone print in ABS, again with an unheated bed.
The setup at present is overly complex although not quite as bad as it looks; a video of the bed vacuum and heater side of the build stage being machined in a re-purposed 3D printer can be seen at https://www.youtube.com/watch?v=Jz5oezLPVYU A recessed grove was cut on the same plate to put resistance wire in for the heater.

I did something similar 3 years ago - it's in my V1 build thread - to print on paper. Paper is fantastic for PLA but difficult to lay down flat without messy adhesives. The vacuum table worked great. An extension of this is to use a roll of paper or other thin material and automate advancing to a fresh surface when the print completes / like an assembly line!

I found paper to be too porous. Although I have done few tests to date, polyester OHP film with grease around the edge seems able to hold a vacuum for some hours without any external vacuum reservoir.

What hot end is that, and why does it have a pipe on it?

The hot end is my own design, the pipe carries air from a positive displacement pump to cool the print very soon after the new filament has been deposited. This does work but I am presently exploring using a perforated ring similar to the "Berd Air" design. Picture below shows a cross section of the hotend.
Mike