Resolution and air tightness
Print all the pieces with 0.2 resolution or lower (Printing them with 0.3 might leave some gaps between the layers and filaments and the membrane enclosure needs to be air tight. If you have a low quality printer, it could be helpful to increase the Extrusion multiplier factor to 1.1 or something like that)
Perforate the lower half
Make a hole into the center of the “Barometer lower half” of the enclosure after printing. It was left un-perforated because it prints better this way.
Find a small jar (between 200cl and 400cl) that has its own sealing cap. Make a hole into the cap large enough for the lower half tube of the printed enclosure to pass through
Attach the flange to the lid
Glue the lower half to the jar cap using an epoxy resin or some thick glue that won’t allow air to escape from the jar. If everything goes well, after you seal the jar, the air from the jar should only communicate to the lower half of the barometer enclosure.
Tighten the flange and membrane
Make a rubber membrane from a rubber glove or a thick balloon and put it between the two half of the enclosure. Tight the flange using M3x10 bolts and nuts.
Hinges and bolts
Insert a small piece of wire or a needle into the rooster’s head using a soldering station or preheating the needle with a lighter.
How to test
After you mount everything together, you should have a visible movement of the needle when you hold the jar into your hands. The mild heating of the jar in this case, causes the air trapped inside to expand and to move the membrane upwards. This quick test reveals if everything is sealed or not.
In order to set the scale to neutral position, open and re close the jar cap in a day with 1013 hPa atmospheric pressure