Step 5Build the Cathode/Vacuum Port
To start construction of this component, remove the screw that comes with the metal doorknob and set it aside. We won't be using it.
Next, drill a 3/16" diameter hole straight through the doorknob starting from the side that the screw was mounted in. The best way to do this is to use progressively larger drill bits to widen the screw threads until they disappear and the hole is wide enough to accommodate the steel brake line. Then, use a smaller bit to drill all the way through the doorknob. It's important that the holes goes all the way through, otherwise, there would be no way for the pump to suck the air out of the bottle. It's also important that the hole be 3/16" wide at the back of the doorknob so that the brake line fits in, but no as wide closer to the front of the doorknob so that it doesn't slide all the way through
One this is done and you have confirmed that the brake line fits snugly into the area where the screw was mounted but does not slide all the way through, apply some epoxy to the inside surface of the hole you drilled and slide the brake line in. Do not allow the epoxy to enter the narrower hole that goes all the way through the doorknob as it might clog it. I attached a diagram and some pictures to better illustrate how all of this is done.
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