To thoughtfulgold; Sorry I missed that last post with your question about the brass tube. I just buy small brass tube sizes from the hobby store (RC airplane store etc) and have stocks in my workshop so I choose the brass tube size based on a snug fit INSIDE the hose. So I just glue in the brass tube and leave 5/8” of brass tube sticking out like a “barb” then press the hose on it. 5 minute epoxy is cheap and common and glues acrylic and brass no problem, so the entire drill+glue thing only takes a few minutes. Generally I don’t bother with proper threaded metal fittings, they are bulky, expensive and heavy.
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On the question of friction, I must admit it has been awhile since I took Newtonian physics in college. But I remember that friction is measured as a force that resists movement. And the amount of friction is the amount of force that it can resist before it reaches failure. So if your penis can resist slipping at 6” hg, but slips when you go over 7” hg, then you could calculate the force on your penis in PSI at 6” hg, and the force at 7” hg, and know that the friction is between those two numbers.
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That all sounds correct, when the skin is adhered to the tube wall you could calculate the friction force by the amount of force you need to apply to break the friction and make it move.
But I believe that once the friction has broken and the skin is sliding on that greasy wall, the friction then has little to no effect and the full piston pull force is applied to the full length of the penis. Then it will settle at the same final length as if the friction was zero or very low. My (crude) measuring experiments at different vacuum settings seem to back that up.
Maybe “sticktion” is a better term than friction? They use that term in suspension mechanics, were the tight rubber seals on the metal suspension tubes cause a sticking effect until enough force is applied to start it moving. And once it starts moving there is a film of grease under the seal so friction is very low once the initial “sticktion” is broken. I think a similar thing happens in pumping; we have a smooth hard surface, a rubbery compliant surface, and grease.
Last edited by RomeoPlus : 01-31-2018 at .